SCMR Edition – Issue 56
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The article discusses new cardiac parametric mapping techniques for T1 and T2 mapping that provide pixel-based maps of myocardial relaxation times. These techniques can detect diffuse myocardial pathologies missed by conventional imaging by quantifying subtle tissue changes. T1 mapping in particular shows potential for diagnosing diseases involving diffuse fibrosis. Standardization of mapping methods is still needed to ensure consistent quantitative results. The efficient, single breath-hold nature of new mapping sequences improves clinical applicability for detecting early disease changes.
![Clinical Cardiology Cardiology Clinical
New Generation Cardiac Parametric Mapping:
the Clinical Role of T1 and T2 Mapping
T1 mapping
Initial T1 measurement methods were
multi-breath-hold. These were time
consuming and clunky, but were able
to measure well diffuse myocardial
fibrosis, a fundamental myocardial
property with high potential clinical
significance [1]. Healthy volunteers
and those with disease had different
extents of diffuse fibrosis [2], and
these were shown to be clinically
significant in a number of diseases.
T1 mapping methods based on the
MOLLI* approach with modifications
for shorter breath-holds, better heart
rate independence and better image
registration for cleaner maps, however,
transformed the field – albeit still
with a variety of potential sequences
in use [3-5]. There are two key ways
of using T1 mapping: Without (or
Viviana Maestrini; Amna Abdel-Gadir; Anna S. Herrey; James C. Moon
The Heart Hospital Imaging Centre, University College London Hospitals, London, UK
designed to optimize contrast
between ‘normal’ and abnormal –
a dichotomy of health and disease. As
a result, global myocardial patholo-gies
such as diffuse infiltration (fibro-sis,
amyloid, iron, fat, pan-inflamma-tion)
are missed.
Recently, rapid technical innovations
have generated new ‘mapping’ tech-niques.
Rather than being ‘weighted’,
these create a pixel map where each
pixel value is the T1 or T2 (or T2*),
displayed in color. These new
sequences are single breath-hold,
increasingly robust and now widely
available. With T1 mapping, clever
contrast agent use also permits the
measurement of the extracellular
volume
(ECV), quantifying the inter-stitium
(odema, fibrosis or amyloid),
also as a map. Early results with these
methodologies are exciting – poten-tially
representing a new era of CMR.
Introduction
Cardiovascular magnetic resonance
(CMR) is an essential tool in cardiol-ogy
and excellent for cardiac function
and perfusion. However, a key, unique
advantage is its ability to directly
scrutinize the fundamental material
properties of myocardium – ‘myocar-dial
tissue characterization’.
Between 2001 and 2011, the key
methods for tissue characterization
have been sequences ‘weighted’ to
a magnetic property – T1-weighted
imaging for scar (LGE) and T2-weighted
for edema (area at risk, myocarditis).
These, particularly LGE imaging, have
changed our understanding and clini-cal
practice in cardiology.
However, there are limitations to
these approaches: Both are difficult
to quantify – the LGE technique in
particular is very robust in infarction,
but harder to quantify in non-ischemic
cardiomyopathy. A more fundamental
difference is that sequences are
before) contrast – Native T1 mapping;
and with contrast, typically by sub-tracting
the pre and post maps with
hematocrit correction to generate
the ECV [6].
Native T1
Native T1 mapping (pre-contrast T1)
can demonstrate intrinsic myocardial
contrast (Fig. 1). T1, measured in mil-liseconds,
is higher where the extra-cellular
compartment is increased.
Fibrosis (focal, as in infarction, or dif-fuse)
[7-8], odema [9-10] and amy-loid
[11], are examples. T1 is lower in
lipid (Anderson Fabry disease, AFD)
[12], and iron [13] accumulation.
These changes are large in some rare
disease. Global myocardial changes
are robustly detectable without con-trast,
even in early disease. In iron, AFD
and amyloid, changes appear before
any other abnormality – there may be
no left ventricular hypertrophy, a nor-mal
electrocardiogram, and normal
conventional CMR, for example – gen-uinely
new information. In established
disease, low T1 values in AFD appear
to absolutely distinguish it from other
causes of left ventricular hypertrophy
[12] whilst in established amyloid T1
elevation tracks known markers of
cardiac severity [11].
A note of caution, however. Native
T1, although stable between healthy
volunteers to 1 part in 30, is depen-dent
on platform (magnet manufac-turer,
sequence and sequence variant,
field strength) [14]. Normal reference
ranges for your setup are needed.
Lowest ECV Tertile
Middle ECV Tertile
Highest ECV Tertile
p < 0.001 fortrend
p < 0.015 for Middle Tertile
compared to others
2 ECV in non scar areas (LGE excluded) is associated with all-cause mortality [21].
The signal acquired is also a compos-ite
signal – generated by both inter-stitium
and myocytes. The use of
an extracellular contrast agent adds
another dimension to T1 mapping
and the ability to characterize the
extracellular compartment specifically.
Extracellular volume (ECV)
Initially, post-contrast T1 was mea-sured,
but this is confounded by renal
clearance, gadolinium dose, body
composition, acquisition time post
bolus, and hematocrit. Better is mea-suring
the ECV. The ratio of change
of T1 between blood and myocardium
after contrast, at sufficient equilibrium
(e.g. after 15 minutes post-bolus – no
infusion generally needed) [15, 16],
represents the contrast agent parti-tion
coefficient [17], and if corrected
for the hematocrit, the myocardial
extracellular space – ECV [1]. The ECV
is specific for extracellular expansion,
and well validated. Clinically this
occurs in fibrosis, amyloid and
odema. To distinguish, the degree of
ECV change and the clinical context
is important. A multiparametric
approach (e. g. T2 mapping or
T2-weighted imaging in addition)
may therefore be useful. Amyloid can
have far higher ECVs than any other
disease [18] whereas ageing has small
changes – near the detection limits,
but of high potential clinical impor-tance
[19, 20]. For low ECV expan-sion
diseases, biases from blood pool
partial volume errors need to be metic-ulously
addressed. Nevertheless, even
modest ECV changes appear prognos-tic.
In 793 consecutive patients
(all-comers but excluding amyloid and
HCM, measuring outside LGE areas)
followed over 1 year, global ECV pre-dicted
short term-mortality (Fig. 2)
2
3A 3B 3C 100%
A patient with myocarditis. On the left side a native T1 map showing the higher T1 value in the inferolateral wall (1115 ms);
in the centre, a post-contrast T1 map showing the shortened T1 value after contrast administration (594 ms); on the right side
the derived ECV map showing higher value of ECV (58%) compared to remote myocardium.
3
0%
Proportion Surviving
Years of Follow-up
1.0
0.9
0.8
0.7
0.6
0.5
0 0.5 1.0 1.5 2.0
* The product is currently under develop-ment;
is not for sale in the U.S. and other
countries, and its future availability cannot
be ensured.
1
Native T1 maps of (1A) healthy
volunteer (author VM): the
myocardium appears homogenously
green and the blood is red; (1B)
cardiac amyloid: the myocardium
has a higher T1 (red); (1C)
Anderson Fabry disease: the
myocardium has a lower T1 (blue)
from lipid – except the inferolateral
wall where there is red from
fibrosis; (1D) myocarditis, the
myocardium has a higher T1 (red)
from edema, which is regional; (1E)
iron overload: the myocardium has
a lower T1 (blue) from iron.
1A 1B 1C
1D 1E
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![Clinical Cardiology Cardiology Clinical
Progress is rapid; challenges remain.
Delivery across sites and standard-ization
is now beginning with new
draft guidelines for T1 mapping
in preparation. Watch this space.
References
1 Flett AS, Hayward MP, Ashworth MT,
Hansen MS, Taylor AM, Elliott PM,
McGregor C, Moon JC. Equilibrium
Contrast Cardiovascular Magnetic
Resonance for the measurement of
diffuse myocardial fibrosis: preliminary
validation in humans. Circulation
2010;122:138-144.
2 Sado DM, Flett AS, Banypersad SM, White
SK, Maestrini V, Quarta G, Lachmann RH,
Murphy E, Mehta A, Hughes DA, McKenna
WJ, Taylor AM, Hausenloy DJ, Hawkins
PN, Elliott PM, Moon JC. Cardiovascular
magnetic resonance measurement of
myocardial extracellular volume in health
and disease. Heart 2012;98:1436-1441.
3 Piechnik SK, Ferreira VM, Dall’Armellina E,
Cochlin LE, Greiser A, Neubauer S,
Robson MD. Shortened Modified Look-
Locker Inversion recovery (ShMOLLI) for
clinical myocardial T1 mapping at 1.5
and 3 T within a 9 heartbeat breathhold.
J Cardiovasc Magn Reson 2010;12:69.
4 Messroghli DR, Greiser A, Fröhlich M,
Dietz R, Schulz-Menger J. Optimization
and validation of a fully-integrated pulse
sequence for modified look-locker
inversion-recovery (MOLLI) T1 mapping
of the heart. J Magn Reson Imaging
2007;26:1081–1086.
5 Fontana M, White SK, Banypersad SM,
Sado DM, Maestrini V, Flett AS, Piechnik
SK, Neubauer S, Roberts N, Moon JC.
Comparison of T1 mapping techniques for
ECV quantification. Histological validation
and reproducibility of ShMOLLI versus
multibreath-hold T1 quantification
equilibrium contrast CMR. J Cardiovasc
Magn Reson 201;14:88.
6 Kellman P, Wilson JR, Xue H, Ugander M,
Arai AE. Extracellular volume fraction
mapping in the myocardium, part 1:
evaluation of an automated method.
J Cardiovasc Magn Reson 2012;14:63.
7 Dass S, Suttie JJ, Piechnik SK, Ferreira VM,
Holloway CJ, Banerjee R, Mahmod M,
Cochlin L, Karamitsos TD, Robson MD,
Watkins H, Neubauer S. Myocardial tissue
characterization using magnetic resonance
non contrast T1 mapping in hypertrophic
and dilated cardiomyopathy. Circ
Cardiovasc Imaging. 2012; 6:726-33.
8 Puntmann VO, Voigt T, Chen Z, Mayr M,
Karim R, Rhode K, Pastor A, Carr-White G,
Razavi R, Schaeffter T, Nagel E. Native T1
mapping in differentiation of normal
myocardium from diffuse disease in
hypertrophic and dilated cardiomy-opathy.
J Am Coll Cardiovasc Imgaging
2013;6:475–84.
Contact
Dr. James C. Moon
The Heart Hospital Imaging Centre
University College London Hospitals
16–18 Westmoreland Street
London W1G 8PH
UK
Phone: +44 (20) 34563081
Fax: +44 (20) 34563086
james.moon@uclh.nhs.uk
4A 4B
4C 4D
(4A) T2 mapping in a normal volunteer (author VM). (4B) High T2 value in patient
with myocarditis – here epicardial edema. (4C) Edema in acute myocardial
infarction – here patchy due to microvascular obstruction – see LGE, (4D).
4
[21]. The same group also found
(n ~1000) higher ECVs in diabetics.
Those on renin-angiotensin-aldoste-rone
system blockade had lower ECVs.
ECV also predicted mortality and/or
incident hospitalization for heart
failure
in diabetics [22].
The use and capability of ECV quanti-fication
is growing. T1 mapping is
getting better and inline ECV maps
are now possible where each pixel
carries directly the ECV value (Fig. 3)
– a more biologically relevant figure
than T1 [6].
T2 mapping
T2-weighted CMR identifies myocar-dial
odema both in inflammatory
pathologies and acute ischemia, delin-eating
the area at risk. However, these
imaging techniques (e. g. STIR) are
fragile in the heart and can be chal-lenging,
both to acquire and to inter-pret.
Preliminary advances were made
with T2-weighted SSFP sequences,
which reduce false negatives and
positives [23, 24]. T2 mapping seems
a further increment [25] (Fig. 4). As
with T1 mapping, global diseases such
as pan-myocarditis may now be iden-tified
by T2 mapping, and preliminary
results are showing this in several
rheumatologic diseases (lupus, sys-temic
capillary leak syndrome) and
transplant rejection, detecting early
rejection missed by other modalities
[26, 27].
Conclusion
Mapping – T1, T2, ECV mapping of
myocardium is an emerging topic with
the potential to be a powerful tool in
the identification and quantification
of diffuse myocardial processes with-out
biopsy. Early evidence suggests
that this technique detects early stage
disease missed by other imaging
methods and has potential as a prog-nosticator,
as a surrogate endpoint
in trials, and to monitor therapy.
9 Ferreira VM, Piechnik SK, Dall’Armellina E,
Karamitsos TD, Francis JM, Choudhury
RP, Friedrich MG, Robson MD, Neubauer
S. Non-contrast T1 mapping detects acute
myocardial edema with high diagnostic
accuracy: a comparison to T2-weighted
cardiovascular magnetic resonance. J
Cardiovasc Magn Reson 2012; 14:42.
10 Dall’Armellina E, Piechnik SK, Ferreira VM,
Si Ql, Robson MD, Francis JM, Cuculi F,
Kharbanda RK, Banning AP, Choudhury
RP, Karamitsos TD, Neubauer S. Cardio-vascular
magnetic resonance by non
contrast T1 mapping allows assessment
of severity of injury in acute myocardial
infarction. J Cardiovasc Magn Reson
2012;14:15.
11 Karamitsos TD, Piechnik SK, Banypersad
SM, Fontana M, MD, Ntusi NB, Ferreira
VM, Whelan CJ, Myerson SG, Robson MD,
Hawkins PN, Neubauer S, Moon JC.
Non-contrast T1 Mapping for the
Diagnosis of Cardiac Amyloidosis.
J Am Coll Cardiol Img 2013;6:488–97.
12 Sado DM, White SK, Piechnik SK,
Banypersad SM, Treibel T, Captur G,
Fontana M, Maestrini V, Flett AS, Robson
MD, Lachmann RH, Murphy E, Mehta A,
Hughes D, Neubauer S, Elliott PM,
Moon JC. Identification and assessment
of Anderson-Fabry Disease by Cardiovas-cular
Magnetic Resonance Non-contrast
myocardial T1 Mapping clinical
perspective. Circ Cardiovasc Imaging
2013;6:392-398.
13 Pedersen SF, Thrys SA, Robich MP, Paaske
WP, Ringgaard S, Bøtker HE, Hansen ESS,
Kim WY. Assessment of intramyocardial
hemorrhage by T1-weighted cardiovas-cular
magnetic resonance in reperfused
acute myocardial infarction. J Cardiovasc
Magn Reson 2012; 14:59.
14 Raman FS, Kawel-Boehm N, Gai N, Freed
M, Han J, Liu CY, Lima JAC, Bluemke DA,
Liu S. Modified look-locker inversion
recovery T1 mapping indices: assessment
of accuracy and reproducibility between
magnetic resonance scanners.
J Cardiovasc Magn Reson 2013; 15:64.
15 White SK, Sado DM, Fontana M, Banypersad
SM, Maestrini V, Flett AS, Piechnik SK,
Robson MD, Hausenloy DJ, Sheikh AM,
Hawkins PN, Moon JC. T1 Mapping for
Myocardial Extracellular Volume
measurement by CMR: Bolus Only Versus
Primed Infusion Technique, 2013 Apr 5
[Epub ahead of print].
16 Schelbert EB, Testa SM, Meier CG,
Ceyrolles WJ, Levenson JE, Blair AJ,
Kellman P, Jones BL, Ludwig DR,
Schwartzman D, Shroff SG, Wong TC.
Myocardial extravascular extracellular
volume fraction measurement by
gadolinium cardiovascular magnetic
resonance in humans: slow infusion
versus bolus. J Cardiovasc Magn Reson
2011, Mar 4;13-16.
17 Flacke SJ, Fischer SE, Lorenz CH.
Measurement of the gadopentetate
dimeglumine partition coefficient in
human myocardium in vivo: normal
distribution and elevation in acute and
chronic infarction. Radiology
2001;218:703-10.
18 Banypersad SM, Sado DM, Flett AS,
Gibbs SDG, Pinney JH, Maestrini V,
Cox AT, Fontana M, Whelan CJ,
Wechalekar AD, Hawkins PN, Moon JC.
Quantification of myocardial extracellular
volume fraction in systemic AL amyloi-dosis:
An Equilibrium Contrast Cardio-vascular
Magnetic Resonance Study.
Circ Cardiovasc Imaging 2013;6:34-39.
19 Ugander M, Oki AJ, Hsu LY, Kellman P,
Greiser A, Aletras AH, Sibley CT, Chen MY,
Bandettini WP, Arai AE. Extracellular
volume imaging by magnetic resonance
imaging provides insights into overt
and sub-clinical myocardial pathology.
Eur Heart J 2012; 33: 1268–1278.
20 Liu CY, Chang Liu Y, Wu C, Armstrong A,
Volpe GJ, van der Geest RJ, Liu Y, Hundley
WG, Gomes AS, Liu S, Nacif M, Bluemke
DA, Lima JAC. Evaluation of age related
interstitial myocardial fibrosis with Cardiac
Magnetic Resonance Contrast-Enhanced
T1 Mapping in the Multi-ethnic Study of
Atherosclerosis (MESA). J Am Coll Cardiol
2013 Jul 3 [Epub ahead of print].
21 Wong TC, Piehler K, Meier CG, Testa SM,
Klock AM, Aneizi AA, Shakesprere J,
Kellman P, Shroff SG, Schwartzman DS,
Mulukutla SR, Simon MA, Schelbert EB.
Association between extracellular matrix
expansion quantified by cardiovascular
magnetic resonance and short-term
mortality. Circulation 2012 Sep
4;126(10):1206-16.
22 Wong TC, Piehler KM, Kang IA, Kadakkal
A, Kellman P, Schwartzman DS, Mulukutla
SR, Simon MA, Shroff SG, Kuller LH,
Schelbert EB. Myocardial extracellular
volume fraction quantified by cardiovas-cular
magnetic resonance is increased
in diabetes and associated with mortality
and incident heart failure admission. Eur
Heart J 2013 Jun 11 [Epub ahead of print].
23 Giri S, Chung YC, Merchant A, Mihai G,
Rajagopalan S, Raman SV, Simonetti OP.
T2 quantification for improved detection
of myocardial edema. J Cardiovasc Magn
Reson 2009; 11:56.
24 Verhaert D, Thavendiranathan P, Giri S,
Mihai G, Rajagopalan S, Simonetti OP,
Raman SV. Direct T2 Quantification of
Myocardial Edema in Acute Ischemic
Injury. J Am Coll Cardiol Img 2011;4:
269-78.
25 Ugander M, Bagi PS, Oki AB, Chen B,
Hsu LY, Aletras AH, Shah S, Greiser A,
Kellman P, Arai AE. Myocardial oedema
as detected by Pre-contrast T1 and T2
CMR delineates area at risk associated
with acute myocardial infarction.
J Am Coll Cardiol Img 2012;5:596–603.
26 ThavendiranathanP, Walls M, Giri S,
Verhaert D, Rajagopalan S, Moore S,
Simonetti OP, Raman SV. Improved
detection of myocardial involvement in
acute inflammatory cardiomyopathies
using T2 Mapping. Circ Cardiovasc
Imaging 2012;5:102-110.
27 Usman AA, Taimen K, Wasielewski M,
McDonald J, Shah S, Shivraman G,
Cotts W, McGee E, Gordon R, Collins JD,
Markl M, Carr JC. Cardiac Magnetic
Resonance T2 Mapping in the monitoring
and follow-up of acute cardiac transplant
rejection: A Pilot Study. Circ Cardiovasc
Imaging. 2012; 6:782-90.
120
ms
0
ms
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![Myocardial T1 Mapping:
Techniques and Clinical Applications
Juliano Lara Fernandes1; Ralph Strecker2; Andreas Greiser3; Jose Michel Kalaf1
1 Radiologia Clinica de Campinas; University of Campinas, Brazil
2 Healthcare MR, Siemens Ltda, Sao Paulo, Brazil
3 MR Cardiology, Siemens Healthcare, Erlangen, Germany
Introduction
Cardiovascular magnetic resonance
(CMR) has been an increasingly used
imaging modality which has experi-enced
significant advancements in
the last years [1]. One of the most
used techniques that have made CMR
so important is late gadolinium
enhancement (LGE) and the demon-stration
of localized areas of infarct
and scar tissue [2–4]. However,
despite being very sensitive to small
areas of regional fibrosis, LGE tech-niques
are mostly dependent on the
comparison to supposedly normal
reference areas of myocardium, thus
not being able to depict more diffuse
disease.
Myocardial interstitial fibrosis, with
a diffuse increase in collagen content
in myocardial volume, develops as a
result of many different stimuli includ-
1A 1B
1C
MOLLI images (1A) with respective signal-time curves (1B) and reconstructed T1 map (1C) at 3T.
The mean T1 time for this patient was 1152 ms (pre-contrast).
1
Cardiology Clinical
Table 1: Comparison of the MOLLI sequences available for T1 mapping
Sequence
Original MOLLI T1 sequence
[15]
Optimized MOLLI sequence
[17]
Shortened MOLLI sequence
[18]
Preparation
Non-selective inversion
recovery
Non-selective inversion
recovery
Non-selective inversion
recovery
Bandwidth 1090 Hz/px 1090 Hz/px 1090 Hz/px
Flip angle 50° 35° 35°
Base matrix 240 192 192
Phase resolution 151 128 144
FOV × % phase 380 × 342 256 × 100 340 × 75
TI 100 ms 100 ms 100 ms
Slice thickness 8 mm 8 mm 8 mm
Acquisition window 191.1 ms 202 ms 206 ms
Trigger delay 300 ms 300 ms 500 ms
Inversions 3 3 3
Acquisition heartbeats 3,3,5 3,3,5 5,5,1
Recovery heartbeats 3,3,1 3,3,1 1,1,1
TI increment 100–150 ms 80 ms 80 ms
Scan time 17 heartbeats 17 heartbeats 9 heartbeats
Spatial resolution 2.26 × 1.58 × 8 mm 2.1 × 1.8 × 8 mm 1.8 × 1.8 × 8 mm
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Clinical Cardiology
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![Clinical Cardiology Cardiology Clinical
2A 2B 3A 3B
curves and map are shown in Figure 1.
One disadvantage of this implementa-tion
of MOLLI is its dependence on
heart rate, mostly true for T1 values
less than 200 msec or greater than
750 msec. However, because the devi-ation
is systematic, raw values can be
corrected using the formula T1corrected =
T1raw – (2.7 × [heart rate -70]), bring-ing
the coefficient of variation down
to 4.6% after applying the correction.
An optimized MOLLI sequence was
subsequently described where heart
rate correction might not be even nec-essary
[17]. In the optimized sequence,
the authors tested variations in readout
flip angle, minimum inversion time,
inversion time increments and number
of pauses between each readout
sequence. The conclusion from these
experiments showed that a flip angle
of 35°, a minimum inversion time of
100 msec, increments of 80 msec and
three heart cycle pauses allowed for
the most accurate measurement of
myocardial T1 (Table 1). Because T1
assessment may be sensitive to motion
artifacts and not all patients might
be able to hold their breaths through-out
all the necessary cardiac cycles
used in MOLLI’s sequence implemen-tation,
more recently a shortened
version sequence (ShMOLLI) using
only 9 heart beats was presented to
account for those limitations [18].
Using incomplete recovery of the lon-gitudinal
magnetization that is cor-rected
directly in the scanner by
conditional
interpretation, ShMOLLI
was directly compared to MOLLI in
patients over a wide range of T1
times and heart rates both at 1.5 and
3T. The results showed that despite
an increase in noise and slight increase
in the coefficient of variation (espe-cially
at 1.5T), T1 times were not sig-nificantly
different using ShMOLLI
with the advantage of much shorter
acquisition times (9.0 ± 1.1 sec versus
17.6 ± 2.9 sec). An example of MOLLI
and ShMOLLI images from the same
patient is presented in Figure
2.
Up to now, after acquiring images
for T1 mapping, one had to analyze
them using in-house developed soft-ware,
dedicated
commercial pro-grams
or open-source solutions [19],
not always a simple and routine task,
leading to difficulty in post-process-ing
the data and generating T1 values.
Recent advances have provided new
inline processing techniques that will
generate the T1 maps automatically
after image acquisition with MOLLI,
without the need for further post-pro-cessing,
accelerating the whole pro-cess.
An example of such automated
T1 map is presented in Figure
3. At
the same time, inline application of
motion correction permits more accu-rate
pixel-wise maps, avoiding errors
due to respiratory deviations. An
example of an image with and with-out
motion correction is presented
in Figure 4.
Clinical applications
Potentially, T1 mapping can be used
to assess any disease that affects the
myocardium promoting diffuse fibro-sis.
However, because of its recent
MOLLI (2A) versus ShMOLLI (2B) in a single patient at 3T post-contrast. The calculated values for the 11 MOLLI images were 551 ms
versus 544 ms for the 8 images of the shMOLLI set. The time to acquire the MOLLI images were 21 seconds versus 14 seconds for the
shMOLLI sequence (with a patient heart rate of 61 bpm).
ing pressure overload, volume
overload,
aging, oxidative stress and
activation of the sympathetic and
renin-angiotensin-aldosterone sys-tem
[5]. Different from replacement
fibrosis, where regional collagen
deposits appear in areas of myocyte
injury, LGE has a limited sensitivity
for interstitial diffuse fibrosis [6].
Therefore, if one wants to image dif-fuse
interstitial fibrosis within the
myocardium other techniques might
be more suitable.
While echocardiogram backscatter
and nuclear imaging techniques may
be applied for that purpose [7, 8],
myocardial tissue characterization is
definitely an area where CMR plays
a large role. While equilibrium contrast
CMR and myocardial tagging have been
shown to reflect diffuse myocardial
fibrosis, T1 mapping techniques have
been most widely used. In the follow-ing,
we describe the developments in
T1 mapping as well as their possible
current and future uses.
T1 mapping
By directly quantifying T1 values
for each voxel in the myocardium,
a parametric map can be generated
representing the T1 relaxation times
of any region of the heart without
the need to compare it to a normal
reference standard before or after
the use of a contrast agent. The first
attempts to measure T1 times in the
myocardium used the original Look-
Locker sequence and were done using
free breathing with acquisition times
of over 1 minute per image [9, 10],
not allowing for pixel-based-mapping
but only for regions-of-interest analy-sis.
Another implementation of
T1 mapping used variable sampling
of the k-space in time (VAST), acquir-ing
images in three to four breath-holds
and correlating that data to
invasive biopsy [11]. Other sequences
have been used for quantification of
T1 as well using inversion recovery
TrueFISP [12, 13] or multishot satura-tion
recovery images [14] but their
reproducibility and accuracy have
not been extensively validated.
The most widely used T1 mapping
sequence is based on the Modified
Look-Locker Inversion-recovery (MOLLI)
technique. Described originally by
Messroghli et al. [15] it consists of a
single shot TrueFISP image with acqui-sitions
over different inversion time
readouts allowing for magnetization
recovery of a few seconds after 3 to
5 readouts. The parameters for the
original MOLLI sequence are described
in Table 1. The advantages of this
sequence over previous methods are
its acquisition in only one relatively
short breath-hold, the higher spatial
resolution (1.6 × 2.3 × 8 mm) and
increased dynamic signal. Reproduc-ibility
studies using this sequence have
shown that the method is very accu-rate
with a coefficient of variation of
5.4% [16] although an underestima-tion
of 8% should be expected based
on phantom data. An example of MOLLI
images and its respective signal-time
2
An example of an automated T1 map generated on the fly with inline processing after acquisition of a MOLLI sequence at 3T.
In (3A) the original images acquired and in (3B) the inline map. The T1 for this patient was calculated at 525 ms post-contrast.
3
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![Clinical Cardiology Cardiology Clinical
development, the technique has only
been evaluated on a small number of
patients although the clinical scenar-ios
are varied.
The first clinical description of direct
T1 mapping in pathological situa-tions
was done in patients with acute
myocardial infarction [20]. While the
authors did not use the described
MOLLI sequence, they did note that
pre-contrast infarct areas had an
18 ± 7% increase in T1 times com-pared
to normal myocardium and that
after contrast the same areas showed
a 27 ± 4% reduction compared to non-infarcted
areas (P < 0.05 for both).
In chronic myocardial infarction,
where LGE has proven so useful, these
changes were also observed although
differences were not as pronounced
as in the acute setting [21].
In amyloidosis, post-contrast T1 times
were also detected to be shorter in
the subendocardial regions compared
to other myocardium areas [22]. The
combination of both LGE identifica-tion
and T1 times < 191 msec in the
subendocardium at 4 minutes pro-vided
a 97% concordance in diagnosis
of cardiac amyloidosis and T1 values
significantly correlated to markers of
amyloid load such as left ventricular
mass, wall thickness, interatrial thick-ness
and diastolic function.
In valve disease, an attempt to show
differences in T1 values in patients
with chronic aortic regurgitation using
MOLLI sequence did not find any
changes in the overall group before
or after contrast [23]. However, the
authors did notice that differences
were observed regionally in segments
that demonstrated impaired wall
motion in cine images. The small num-ber
of patients (n = 8) in the study
might have affected the conclusions
and further evaluation of similar data
might yield other conclusions. A more
recent study showed that, using equi-librium
contrast CMR, diffuse fibrosis
measured in aortic stenosis patients
provided significant correlations to
quantification on histology [24].
In heart failure, the use of T1 map-ping
has been more widely studied
and directly correlated to histology
evaluation [11]. In this paper, the
authors evaluated patients with isch-emic,
idiopathic and restrictive car-diomyopathies
showing that post-contrast
T1 times at 1.5T were
significantly shorter than controls
even after exclusion of areas of LGE
(429 ± 22 versus 564 ± 23 msec,
P < 0.0001). We have investigated
a similar group of patients on a 3T
MAGNETOM Verio scanner and have
found that both dilated and hypertro-phic
cardiomyopathy patients have
lower post-contrast T1 times com-pared
to controls, but non-infarcted
areas from ischemic cardiomyopathy
patients do not show significant
differences
(unpublished data).
Examples of a myocardial T1 map at
3T from a patient with dilated cardio-myopathy
and suspected hypertro-phic
cardiomyopathy are seen in Fig-ure
5 and 6 respectively.
Finally, in patients with both type 1
and 2 diabetes melitus, T1 mapping
using CMR was able to show that these
patients may have increased interstitial
fibrosis compared to controls as T1
times were significantly shorter (425 ±
72 msec versus 504 ± 34 msec,
P < 0.001) and correlated to global
longitudinal strain by echocardiography,
demonstrating impaired myocardial
systolic function.
Future directions
Certainly with the research of T1
mapping in different clinical scenarios
the applicability of the method will
increase substantially. In the mean-time,
more effort has been made to
further standardize values across dif-ferent
patients and time points. As T1
time, especially after injection of con-trast,
depends on both physiologic and
scan acquisitions, methods have been
described to account for these factors,
with normalization of T1 values [25].
More than that, standardization of
normal values across a larger number
of normal individuals is also necessary
since most papers provide data on
much reduced cohorts, mostly limited
to single center data. In that regard,
a large multicenter registry is already
collecting data at 3T in patients from
20 to 80 years of age in Latin America
[Fernandes JL et al. – www.clinicaltri-als.
gov – NCT01030549]. Besides that,
other techniques are under develop-ment
that might allow T1 measurement
with larger coverage of the heart using
3D methods [26].
Nevertheless, with the current tech-niques
available there are already much
more clinical applications to explore
and certainly quantitative T1 mapping
will become one of the key applica-tions
in CMR in the near future.
4A
4B
4
Example of a
MOLLI sequence
obtained without
(4A) and with (4B)
motion correction.
Notice the
deviation from
baseline of the left
ventricle during
the image acqui-sition
cycle, fully
corrected in (4B).
References
1 Fernandes JL, Pohost GM. Recent advances
in cardiovascular magnetic resonance. Rev
Cardiovasc Med 2011;12:e107-12.
2 Kim RJ, Wu E, Rafael A, et al. The use of
contrast-enhanced magnetic resonance
imaging to identify reversible myocardial
dysfunction. N Engl J Med 2000;343:
1445-53.
3 Assomull RG, Prasad SK, Lyne J, et al.
Cardiovascular magnetic resonance,
fibrosis, and prognosis in dilated cardiomy-opathy.
J Am Coll Cardiol 2006;48:
1977-85.
4 Ordovas KG, Higgins CB. Delayed contrast
enhancement on MR images of
myocardium: past, present, future.
Radiology 2011;261:358-74.
5 Jellis C, Martin J, Narula J, Marwick TH.
Assessment of nonischemic myocardial
fibrosis. J Am Coll Cardiol 2010;56:89-97.
6 Mewton N, Liu CY, Croisille P, Bluemke D,
Lima JA. Assessment of myocardial fibrosis
with cardiovascular magnetic resonance. J
Am Coll Cardiol 2011;57:891-903.
7 Picano E, Pelosi G, Marzilli M, et al. In vivo
quantitative ultrasonic evaluation of
myocardial fibrosis in humans. Circulation
1990;81:58-64.
17 Messroghli DR, Greiser A, Frohlich M,
Dietz R, Schulz-Menger J. Optimization
and validation of a fully-integrated
pulse sequence for modified look-locker
inversion-recovery (MOLLI) T1
mapping of the heart. J Magn Reson
Imaging 2007;26:1081-6.
18 Piechnik SK, Ferreira VM,
Dall’Armellina E, et al. Shortened
Modified Look-Locker Inversion
recovery (ShMOLLI) for clinical
myocardial T1 mapping at 1.5 and 3 T
within a 9 heartbeat breathhold. J
Cardiovasc Magn Reson 2010;12:69.
19 Messroghli DR, Rudolph A, Abdel-Aty
H, et al. An open-source software tool
for the generation of relaxation time
maps in magnetic resonance imaging.
BMC Med Imaging 2010; 10:16.
20 Messroghli DR, Niendorf T, Schulz-
Menger J, Dietz R, Friedrich MG. T1
mapping in patients with acute
myocardial infarction. J Cardiovasc
Magn Reson 2003;5:353-9.
21 Messroghli DR, Walters K, Plein S,
et al. Myocardial T1 mapping: appli-cation
to patients with acute and
chronic myocardial infarction. Magn
Reson Med 2007;58:34-40.
22 Maceira AM, Joshi J, Prasad SK, et al.
Cardiovascular magnetic resonance
in cardiac amyloidosis. Circulation
2005;111:186-93.
23 Sparrow P, Messroghli DR, Reid S,
Ridgway JP, Bainbridge G, Sivana-nthan
MU. Myocardial T1 mapping
for detection of left ventricular
myocardial fibrosis in chronic aortic
regurgitation: pilot study. AJR Am J
Roentgenol 2006;187:W630-5.
24 Flett AS, Hayward MP, Ashworth MT,
et al. Equilibrium contrast cardiovas-cular
magnetic resonance for the
measurement of diffuse myocardial
fibrosis: preliminary validation in
humans. Circulation 2010;
122:138-44.
8 van den Borne SW, Isobe S, Verjans JW,
et al. Molecular imaging of interstitial
alterations in remodeling myocardium
after myocardial infarction. J Am Coll
Cardiol 2008;52:2017-28.
9 Flacke SJ, Fischer SE, Lorenz CH.
Measurement of the gadopentetate
dimeglumine partition coefficient in
human myocardium in vivo: normal
distribution and elevation in acute and
chronic infarction. Radiology
2001;218:703-10.
10 Brix G, Schad LR, Deimling M, Lorenz WJ.
Fast and precise T1 imaging using a
TOMROP sequence. Magn Reson Imaging
1990;8:351-6.
11 Iles L, Pfluger H, Phrommintikul A, et al.
Evaluation of diffuse myocardial fibrosis
in heart failure with cardiac magnetic
resonance contrast-enhanced T1
mapping. J Am Coll Cardiol 2008;52:
1574-80.
12 Schmitt P, Griswold MA, Jakob PM, et al.
Inversion recovery TrueFISP: quantifi-cation
of T(1), T(2), and spin density.
Magn Reson Med 2004;51:661-7.
13 Bokacheva L, Huang AJ, Chen Q, et al.
Single breath-hold T1 measurement using
low flip angle TrueFISP. Magn Reson Med
2006;55:1186-90.
14 Wacker CM, Bock M, Hartlep AW, et al.
Changes in myocardial oxygenation and
perfusion under pharmacological stress
with dipyridamole: assessment using T*2
and T1 measurements. Magn Reson Med
1999;41:686-95.
15 Messroghli DR, Radjenovic A, Kozerke S,
Higgins DM, Sivananthan MU, Ridgway JP.
Modified Look-Locker inversion recovery
(MOLLI) for high-resolution T1 mapping
of the heart. Magn Reson Med 2004;52:
141-6.
16 Messroghli DR, Plein S, Higgins DM, et al.
Human myocardium: single-breath-hold
MR T1 mapping with high spatial
resolution--reproducibility study.
Radiology 2006;238:1004-12.
Reprinted from MAGNETOM Flash 1/2012 Reprinted from MAGNETOM Flash 1/2012
14 MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world 15](https://image.slidesharecdn.com/magnetomflash56scmr-01331257-140821155659-phpapp02/85/SCMR-Edition-Issue-56-8-320.jpg)
![Clinical Cardiovascular Imaging Cardiovascular Imaging Clinical
Preliminary Experiences with Compressed
Sensing Multi-Slice Cine Acquisitions for
the Assessment of Left Ventricular Function:
CV_sparse WIP
G. Vincenti, M.D.1; D. Piccini2,4; P. Monney, M.D.1; J. Chaptinel3; T. Rutz, M.D.1; S. Coppo3; M. O. Zenge, Ph.D.4;
M. Schmidt4; M. S. Nadar5; Q. Wang5; P. Chevre1, 6; M.; Stuber, Ph.D.3; J. Schwitter, M.D.1
1 Division of Cardiology and Cardiac MR Center, University Hospital of Lausanne (CHUV), Lausanne, Switzerland
2 Advanced Clinical Imaging Technology, Siemens Healthcare IM BM PI, Lausanne, Switzerland
3 Department of Radiology, University Hospital (CHUV) and University of Lausanne (UNIL) / Center for Biomedical Imaging
(CIBM), Lausanne, Switzerland
4 MR Applications and Workflow Development, Healthcare Sector, Siemens AG, Erlangen, Germany
5 Siemens Corportate Technology, Princeton, USA
6 Department of Radiology, University Hospital Lausanne, Switzerland
ize pathological myocardial tissue was
the basis to assign a class 1 indication
for patients with known or suspected
heart failure to undergo CMR in the
new Heart Failure Guidelines of the
European Society of Cardiology [3].
decision making [3] e.g. to start [4]
or stop [5] specific drug treatments
or to implant devices [6]. CMR is
generally accepted as the gold stan-dard
method to yield most accurate
measures of LV ejection fraction and
LV volumes. This capability and the
additional value of CMR to character-
Introduction
Left ventricular (LV) ejection fraction
is one of the most important measures
in cardiology and part of every car-diac
imaging evaluation as it is recog-nized
as one of the strongest predic-tors
of outcome [1]. It allows to assess
the effect of established or novel
treatments [2], and it is crucial for
The evaluation of LV volumes and LV
ejection fraction are based on well-defined
protocols [7] and it involves
the acquisition of a stack of LV short
axis cine images from which volumes
are calculated by applying Simpson’s
rule. These stacks are typically acquired
in multiple breath-holds. Quality crite-ria
[8] for these functional images are
available and are implemented e.g.
for the quality assessment within the
European CMR registry which currently
holds approximately 33,000 patients
and connects 59 centers [9].
Recently, compressed sensing (CS)
techniques emerged as a means to
considerably accelerate data acquisi-tion
without compromising signifi-cantly
image quality. CS has three
requirements:
1) transform sparsity,
2) incoherence of undersampling
artifacts,
and
3) nonlinear reconstruction (for
details, see below).
Based on these prerequisites, a CS
approach for the acquisition of cardiac
cine images was developed and
tested*. In particular, the potential to
acquire several slices covering the
heart in different orientations within
a single breath-hold would allow to
apply model-based analysis tools
which theoretically could improve the
motion assessment at the base of the
heart, where considerable through-plane
motion on short-axis slices can
introduce substantial errors in LV
volume and LV ejection fraction cal-culations.
Conversely, with a multi-breath-
hold approach, there are typi-cally
small differences in breath-hold
positions which can introduce errors
in volume and function calculations.
The pulse sequence tested here
allows for the acquisition of 7 cine
slices within 14 heartbeats with an
excellent temporal and spatial
resolution.
Such a pulse sequence would also
offer the advantage to obtain func-tional
information in at least a single
plane in patients unable to hold their
breath for several heartbeats or in
patients with frequent extrasystoles
or atrial fibrillation. However, it should
be mentioned that accurate quantita-tive
measures of LV volumes and
function cannot be obtained in highly
arrhythmic hearts or in atrial fibrilla-tion,
as under such conditions vol-umes
and ejection fraction change
from beat to beat due to variable fill-ing
conditions. Nevertheless, rough
estimates of LV volumes and function
would still be desirable in arrhythmic
patients.
In a group of healthy volunteers and
patients with different LV patholo-gies,
the novel single-breath-hold CS
cine approach was compared with
the standard multi-breath-hold cine
technique with respect to measure
LV volumes and LV ejection fraction.
The CV_sparse
work-in-progress
(WIP)
The CV_sparse WIP package imple-ments
sparse, incoherent sampling
and iterative reconstruction for car-diac
applications. This method in
principle allows for high acceleration
factors which enable triggered 2D
real-time cine CMR while preserving
high spatial and/or temporal resolu-tion
of conventional cine acquisi-tions.
Compressed sensing methods
exploit the potential of image com-pression
during the acquisition of
raw input data. Three components
[10] are crucial for the concept of
compressed sensing to work
I. Sparsity: In order to guarantee
compressibility of the input data,
sparsity must be present in a specific
transform domain. Sparsity can be
computed e.g. by calculating differ-ences
between neighboring pixels
or by calculating finite differences in
angiograms which then detect pri-marily
vessel contours which typically
1
* Work in progress: The product is still under
development and not commercially available
yet. Its future availability cannot be ensured.
1 Display of the represent a few percent of the
planning of the
7 slices (4 short
axis and 3 long
axis slices)
acquired within
a single breath-hold
with the
three localizers.
1
2A 2B
Displays of the data analysis tools for the conventional short axis stack of cine images covering the entire LV (2A) and the 4D
analysis tool (2B), which is model-based and takes long axis shortening of the LV, i.e. mitral annulus motion into account.
Note that with both analysis tools, LV trabeculations are included into the LV volume, particularly in the end-diastolic images
(corresponding images on the left of top row in 2A and 2B).
2
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![Clinical Cardiovascular Imaging Cardiovascular Imaging Clinical
entire image data only. Furthermore,
sparsity is not limited to the spatial
domain: the acquisition of cine
images of the heart can be highly
sparsified in the temporal dimension.
II. Incoherent sampling: The alias-ing
artifacts due to k-space unders-ampling
must be incoherent, i.e.
noise-like, in that transform domain.
Here, it is to mention that fully ran-dom
k-space sampling is suboptimal
as k-space trajectories should be
smooth for hardware and physiologi-cal
considerations. Therefore, inco-herent
sampling schemes must be
designed to avoid these concerns
while fulfilling the condition of ran-dom,
i.e. incoherent sampling.
III. Reconstruction: A non-linear iter-ative
optimization corrects for sub-sampling
artifacts during the process
of image reconstruction yielding to a
best solution with a sparse
representation
in a specific transform
domain and which is consistent with
the input data. Such compressed
sensing techniques can also be com-bined
with parallel imaging tech-niques
[11].
WIP CV_sparse Sequence
The current CV_sparse sequence [12]
realizes incoherent sampling by
initially
distributing the readouts
pseudo-randomly on the Cartesian
grid in k-space. In addition, for
cine-CMR imaging, a pseudo-random
offset
is applied from frame-to-frame
which results in an incoherent tem-poral
jitter. Finally, a variable sam-pling
density in k-space stabilizes
the iterative reconstruction. To avoid
eddy current effects for balanced
steady-state free precession (bSSFP)
acquisitions, pairing [13] can also be
applied. Thus, the tested CV_sparse
sequence is characterized by sparse,
incoherent sampling in space and
time, non-linear iterative reconstruc-tion
integrating SENSE, and L1 wave-let
regularization in the phase encod-ing
direction and/or the temporal
dimension. With regard to reconstruc-tion,
the ICE program runs a non-linear
iterative reconstruction with
k-t regularization in space and time
specifically modified for compressed
sensing. The algorithm derives from
a parallel imaging type reconstruc-tion
which takes coil sensitivity maps
into account, thus supporting pre-dominantly
high acceleration factors.
For cine CMR, no additional reference
scans are needed because – similar
to TPAT – the coil sensitivity maps are
calculated from the temporal average
of the input data in a central region
of k-space consisting of not more
than 48 reference lines. The exten-sive
calculations for image recon-struction
typically running 80 itera-tions
are performed online on all
CPUs on the MARS computer in paral-lel,
in order to reduce reconstruction
times.
Volunteer and Patient
studies
In order to obtain insight into the
image quality of single-breath-hold
multi-slice cine CMR images acquired
with the compressed sensing (CS)
approach, we studied a group of
healthy volunteers and a patient
group with different pathologies of
the left ventricle. In addition to the
evaluation of image quality, the
robustness and the precision of the
CS approach for LV volumes and LV
ejection fraction was also assessed in
comparison with a standard high-resolution
cine CMR approach. All CMR
examinations were performed on a
1.5T MAGNETOM Aera (Siemens
Healthcare, Erlangen, Germany). The
imaging protocol consisted of a set
of cardiac localizers followed by the
acquisition of a stack of conventional
short-axis SSFP cine images covering
the entire LV with a spatial and tem-poral
resolution of 1.2 x 1.6 mm2,
and approximately 40 ms, respectively
(slice thickness: 8 mm; gap between
slices: 2 mm). LV 2-chamber, 3-cham-ber,
and 4-chamber long-axis acquisi-tions
were obtained for image quality
assessment but were not used for LV
volume quantifications. As a next step,
to test the new CS-based technique,
slice orientations were planned to cover
the LV with 4 short-axis slices distrib-uted
evenly over the LV long axis com-plemented
by 3 long-axis slices (i.e. a
2-chamber, 3-chamber, and 4-chamber
slice) (Fig. 1). These 7 slices were
then acquired in a single breath-hold
maneuver lasting 14 heart beats (i.e.
2 heart beats per slice) resulting in an
acceleration factor of 11.0 with a tem-poral
and spatial resolution of 30 ms
and 1.5 x 1.5 mm2, respectively (slice
thickness: 6 mm). As the reconstruc-tion
algorithm is susceptible
to aliasing
in the phase-encoding direction, the
7 slices were first acquired with a non-cine
acquisition to check for correct
phase-encoding directions and, if
needed, to adjust the field-of-view
to avoid fold-over artifacts. After
confirmation
of correct imaging
parameters, the 7-slice single-breath-
hold cine CS-acquisition was
performed. In order to obtain a refer-ence
for the LV volume measurement,
a phase-contrast flow measurement
in the ascending aorta was per-formed
to be compared with the
LV stroke volumes calculated from
the standard and CS cine data.
The conventional stack of cine SSFP
images was analyzed by the Argus
software (Siemens Argus 4D Ventric-ular
Function, Fig. 2A). The CS cine
data were analyzed by the 4D-Argus
software (Siemens Argus, Fig. 2B).
Such software is based on an LV
model and, with relatively few opera-tor
interactions, the contours for the
LV endocardium and epicardium are
generated by the analysis tool. Of
note, this 4D analysis tool automati-cally
tracks the 3-dimensional motion
of the mitral annulus throughout the
cardiac cycle which allows for an
accurate volume calculation particu-larly
at the base of the heart.
Results and discussion
Image quality – robustness
of the technique
Overall, a very good image quality
of the single-breath-hold multi-slice
CS acquisitions was obtained in the
12 volunteers and 14 patient studies.
All CS data sets were of adequate
quality to undergo 4D analysis. Small
structures such as trabeculations
were visualized in the CS data sets
as shown in Figures 3 and 4. However,
very small structures, detectable by
the conventional cine acquisitions,
were less well discernible by the CS
images. Therefore, it should be men-tioned
here, that this accelerated
single-
breath-hold CS approach would
be adequate for functional measure-ments,
i.e. LV ejection fraction
assessment (see also results below),
whereas assessment of small struc-tures
as present in many cardiomyop-athies
is more reliable when per-formed
on conventional cine images.
Temporal resolution of the new tech-nique
appears adequate to even
detect visually the dyssynchroneous
contraction pattern in left bundle
branch block. Also, the image con-trast
between the LV myocardium
and the blood pool was high on the
CS images allowing for an easy
assessment of the LV motion pattern.
As a result, the single-breath-hold
cine approach permits to reconstruct
the LV in 3D space with high tempo-ral
resolution as illustrated in Figure
5. Since these data allow to correctly
include the 3D motion of the base
of the heart during the cardiac cycle,
the LV stroke volume appears to be
measurable by the CS approach with
higher accuracy than with the con-ventional
multi-breath-hold approach
(see results below). With an accurate
measurement of the LV stroke vol-ume,
the quantification of a mitral
insufficiency should theoretically ben-efit
(when calculating mitral regurgi-tant
volume as ‘LV stroke volume
minus aortic forward-flow volume’).
As a current limitation of the CS
approach, its susceptibility for fold-over
artifacts should be mentioned
(Figs. 6A). Therefore, the field-of-view
must cover the entire anatomy
and thus, some penalty in spatial res-
Standard cine
9 heartbeats
CV_SPARSE
3 heartbeats
CV_SPARSE
2 heartbeats
CV_SPARSE
1 heartbeat
Examples of visualization of small trabecular structures in the LV (in the rectangle) with the standard cine SSFP sequence (image
on the left) and the accelerated compressed sensing sequences (images on the right). Despite increasing acceleration most infor-mation
on small intraluminal structures remains visible.
3
RCA
Example demonstrating the performance of the compressed sensing
technique visualizing small structures such as the right coronary artery
(RCA) with high temporal and spatial resolution acquired within 2 heart-beats.
Short-axis view of the base of the heart (1 out of 17 frames).
4
3
4
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![Clinical Cardiovascular Imaging Cardiovascular Imaging Clinical
olution may occur in relation to the
patient’s anatomy. In addition, the
sparsity in the temporal domain may
be limited in anatomical regions of
very high flow, and therefore, in
some acquisitions, flow-related arti-facts
occurred in the phase-encoding
direction during systole (Figs. 6B, C).
Also, in its current version, the
sequence is prospective, thus it does
not cover the very last phases of the
cardiac cycle and the reconstruction
times for the CS images lasted sev-eral
minutes precluding an immediate
assessment of the image data quality
or using this image information to
plan next steps of a CMR examination.
Performance of the single-breath-
hold CS approach in
comparison with the stan-dard
multi-breath-hold cine
approach
From a quantitative point-of-view,
the accurate and reliable measure-ment
of LV volumes and function is
crucial as many therapeutic decisions
directly depend on these measures
[3–6]. In this current relatively small
study group, LV end-diastolic and
end-systolic volumes measured by
the single-breath-hold CS approach
were comparable with those calcu-lated
from the standard multi-breath-hold
cine SSFP approach. LVEDV and
LVESV differed by 10 ml ± 17 ml and
2 ml ± 12 ml, respectively. Most impor-tantly,
LV ejection fraction differed
by only 1.3 ± 4.7% (50.6% vs 49.3%
for multi-breath-hold and single-breath-hold,
respectively, p = 0.17; regres-sion:
r = 0.96, p < 0.0001; y = 0.96x +
0.8 ml). Thus, it can be concluded that
the single-breath-hold CS approach
could potentially replace the multi-breath-
hold standard technique for the
assessment of LV volumes and systolic
function.
What about the accuracy of
the novel single-breath-hold
CS technique?
To assess the accuracy of the LV vol-ume
measurements, LV stroke volume
was compared with the LV output
measured in the ascending aorta with
phase-contrast MR. As the flow mea-surements
were performed distally to
the coronary arteries, flow in the coro-naries
was estimated as the LV mass
multiplied by 0.8 ml/min/g. An excel-lent
agreement was found with a
mean of 86.8 ml/beat for the aortic
flow measurement and 91.9 ml/beat
for the LV measurements derived
from the single-breath-hold CS data
(r = 0.93, p < 0.0001). By Bland-Altman
analysis, the stroke volume approach
overestimated by 5.2 ml/beat versus
the reference flow measurement. For
the conventional stroke volume mea-surements,
this difference was 15.6
ml/beat (linear regression analysis vs
aortic
flow: r = 0.69, p < 0.01). More
importantly, the CS LV stroke data were
not only more precise with a smaller
mean difference, the variability of the
CS data vs the reference flow data was
less with a standard deviation as low
as 6.8 ml/beat vs 12.9 ml/beat for the
standard multi-breath-hold approach
(Fig. 7). Several explanations may apply
for the higher accuracy of the single-breath-
hold multi-slice CS approach in
comparison to the conventional multi-breath-
hold approach:
1) With the single-breath-hold
approach, all acquired slices are cor-rectly
co-registered, i.e. they are cor-rectly
aligned in space, a prerequisite
for the 4D-analysis tool to work
properly.
2) This 4D-analysis tool allows for an
accurate tracking of the mitral valve
plane motion during the cardiac cycle
as shown in Figure 5, which is impor-tant
as the cross-sectional area of the
heart at its base is large and thus, inac-curate
slice positioning at the base of
Display of the 3D reconstruction derived from the 7 slices acquired within a single breath-hold. Note the long-axis shortening of the
LV during systole allowing for accurate LV volume measurements (5A, 5B, yellow plane). Any orientation of the 3D is available for
inspection of function (5A–D).
5
6A
A typical fold-over
artifact along the
phase-encoding
direction in a short
axis slice, oriented
superior-inferior for
demonstrative
purpose.
6B
No flow-related
artifacts are
visible on the
end-diastolic
phases, while
small artifacts in
phase-encoding
direction (Artif,
arrows) occur in
mid-systole
projecting over
the mitral valve
(6C).
5A 5B
5C 5D
6A
6B
6C
Artif
Artif
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![Clinical Cardiovascular Imaging Cardiovascular Imaging Clinical
50 60 70
120 130
130
120
110
100
90
80
70
the heart with conventional short-axis
slices typically translate in
relatively large errors. Nevertheless,
we observed a systematic overesti-mation
of the stroke volume by the
CS approach of 5.2 ml/beat in com-parison
to the flow measurements.
In normal hearts with tricuspid aortic
valves, an underestimation of aortic
flow by the phase-contrast technique
is very unlikely [14]. Thus, overesti-mation
of stroke volume by the volume
approach is to consider. In the vol-ume
contours, the papillary muscles
are excluded as illustrated in Figure 8.
As these papillary muscles are excluded
in both the diastolic and systolic con-tours,
this aspect should not affect
net LV stroke volume. However, as
shown in Figure 8, smaller trabecula-tions
of the LV wall are included into
the LV blood pool contour in the
diastolic
phase, while these trabecu-lations,
CS technique
Standard technique
when compacted in the
end-
systolic phase, are excluded from
the blood pool resulting in a small
overestimation of the end-diastolic
volume, and thus, LV stroke volume.
This explanation is likely as Van
Rossum
et al. demonstrated a slight
underestimation of the LV mass when
calculated on end-diastolic phases
versus end-systolic phases, as trabec-ulations
in end-diastole are typically
excluded from the LV walls [15].
In summary, this novel very fast
acquisition strategy based on a CS
technique allows to cover the entire
LV with high temporal and spatial
resolution within a single breath-hold.
The image quality based on these
preliminary results appears adequate
to yield highly accurate measures
of LV volumes, LV stroke volume,
LV mass, and LV ejection fraction.
7
Testing of this very fast multi-slice cine
approach for the atria and the right
ventricle is currently ongoing. Finally,
these preliminary data show that com-pressed
sensing MR acquisitions in
the heart are feasible in humans and
compressed sensing might be imple-mented
for other important cardiac
sequences such as fibrosis/viability
imaging, i.e. late gadolinium enhance-ment,
coronary MR angiography, or
MR first-pass perfusion.
The Cardiac MR Center of the
University Hospital Lausanne
The Cardiac Magnetic Resonance Center
(CRMC) of the University Hospital of
Lausanne (Centre Hospitalier Universi-taire
Vaudois; CHUV) was established
in 2009. The CMR center is dedicated
to high-quality clinical work-up of car-diac
patients, to deliver state-of-the-art
training in CMR to cardiologists and
radiologists, and to pursue research.
In the CMR center education is pro-vided
for two specialties while focus-ing
on one organ system. Traditionally,
radiologists have focussed on using
one technique for different organs,
while cardiologists have concentrated
on one organ and perhaps one tech-nique.
Now in the CMR center the
focus is put on a combination of spe-cialists
with different background on
one organ. Research at the CMR center
is devoted to four major areas: the
study of
1.) cardiac function and tissue charac-terization,
specifically to better under-stand
diastolic dysfunction,
2.) the development of MR-compatible
cardiac devices such as pacemakers
and ICDs;
3.) the utilization of hyperpolarized
13C-carbon contrast media to investi-gate
metabolism in the heart, and
An excellent corre-lation
is obtained for
the LV stroke volume
calculated from the
compressed sensing
data with the flow
volume in the aorta
measured by phase-contast
technique.
Variability of the
conventional LV
stroke volume data
appears higher than
for the compressed
sensing data.
LV stroke volume: comparison vs aortic forward flow
LV short-axis slice: CV_SPARSE
4.) the development of 19F-fluorine-based
CMR techniques to detect
inflammation and to label and track
cells non-invasively.
For the latter two topics, the CMR
center established tight collabora-tions
with the Center for Biomedical
Imaging (CIBM), a network around
Lake Geneva that includes the Ecole
Polytechnique Fédérale de Lausanne
(EPFL), and the universities and uni-versity
hospitals of Lausanne and
Geneva. In particular, strong collab-orative
links are in place with the
CVMR team of Prof. Matthias Stuber,
a part of the CIBM and located at the
University Hospital Lausanne and
with Prof. A. Comment, with whom
we perform the studies on real-time
metabolism based on the 13C-carbon
hyperpolarization (DNP) technique.
In addition, collaborative studies are
ongoing with the Heart Failure and
Cardiac Transplantation Unit led by
Prof. R. Hullin (detection of graft
rejection by tissue characterization)
and the Oncology Department led
by Prof. Coukos (T cell tracking by19F-
MRI in collaboration with Prof.
Stuber, R. van Heeswijk, CIBM, and
Prof. O. Michielin, Oncology). This
structure allows for a direct interdis-ciplinary
interaction between physi-cians,
engineers, and basic scientists
on a daily basis with the aim to
enable innovative research and fast
translation of these techniques from
bench to bedside.
The CMRC is also the center of com-petence
for the quality assessment of
the European CMR registry which
holds currently approximately 33,000
patient studies acquired in 59 centers
across Europe.
The members of the CRMC team are:
Prof. J. Schwitter (director of the
center),
PD Dr. X. Jeanrenaud, Dr. D.
Locca, MER, Dr. P. Monney, Dr. T.
Rutz, Dr. C. Sierro, and Dr. S. Koest-ner
(cardiologists, staff members),
Overestimation of end-diastolic LV volumes by volumetric measurements. In comparison to ejected blood from the LV as measured
with phase-contrast techniques, the volumetric measurements of LV stroke volume overestimated by approximately 5 ml, most
likely by overestimation of LV end-diastolic volume. Small trabculations (yellow contours in 8A) are included into the LV blood
volume (red contour in 8A) in diastole, while these trabeculations (yellow contours in 8B) are typically included in the end-systolic
phase (red contours in 8B). For the same reasons, LV mass (= green contour minus red contour) is often slightly underestimated in
diastole vs systole.
8
7
8A 8B
End-diastolic frame End-systolic frame
ml/beat (aortic forward flow by PC)
ml/beat (LV stroke volume)
80 90 100 110
60
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![References
1 Curtis JP, Sokol SI, Wang Y, Rathore SS,
Ko DT, Jadbabaie F, Portnay EL, Marshalko
SJ, Radford MJ, Krumholz HM. The associ-ation
of left ventricular ejection fraction,
mortality, and cause of death in stable
outpatients with heart failure. Journal of
the American College of Cardiology.
2003;42(4):736-42.
2 Sürder D, Manka R, Lo Cicero V, Moccetti T,
Rufibach K, Soncin S, Turchetto L,
Radrizzani M, Astori G, Schwitter J, Erne P,
Jamshidi P, Auf Der Maur C, Zuber M,
Windecker S, Moschovitis A, Wahl A,
Bühler I, Wyss C, Landmesser U, Lüscher T,
Corti R. Intracoronary injection of bone
marrow derived mononuclear cells, early
or late after acute myocardial infarction:
Effects on global LV-function: 4 months
results of the SWISS-AMI trial. Circulation.
2013;127:1968-79.
11 Liang D, Liu B, Wang J, Ying L. Accelerating
SENSE using compressed sensing. Magnetic
Resonance in Medicine. 2009;62(6):
1574-84.
12 Liu J. Dynamic cardiac MRI reconstruction
with weighted redundant Haar wavelets.
Magn Reson Med. 2012;Proc. ISMRM
2012,abstract.
13 Bieri O, Markl M, Scheffler K. Analysis
and compensation of eddy currents in
balanced SSFP. Magn Reson Med.
2005;54:129-37.
14 Muzzarelli S, Monney P, O’Brien K, Faletra F,
Moccetti T, Vogt P, Schwitter J. Quantifi-cation
of aortic valve regurgitation by
phase-contrast magnetic resonance in
patients with bicuspid aortic valve: where
to measure the flow? . Eur Heart J - CV
Imaging. 2013:in press.
15 Papavassiliu T, Kühl HP, Schröder M,
Süselbeck T, Bondarenko O, Böhm CK,
Beek A, Hofman MMB, van Rossum AC.
Effect of Endocardial Trabeculae on
Left Ventricular Measurements and
Measurement Reproducibility at Cardio-vascular
MR Imaging1. Radiology. 2005
July 1, 2005;236(1):57-64.
Contact
Professor Juerg Schwitter
Médecin Chef Cardiologie
Directeur du Centre de la RM
Cardiaque du CHUV
Centre Hospitalier
Universitaire
Vaudois – CHUV
Rue du Bugnon 46
1011 Lausanne
Suisse
Phone: +41 21 314 0012
jurg.schwitter@chuv.ch
www.cardiologie.chuv.ch
Dr. G. Vincenti (cardiologist) and
Dr. N. Barras (cardiologist in training,
rotation), PD. Dr. S. Muzzarellli (affili-ated
cardiologist), Prof. C. Beigelman
and Dr. X. Boulanger (radiologists,
staff members), Dr. G.L. Fetz (radiol-ogist
in training, rotation), C. Gonza-les,
PhD (19F-fluorine project leader),
H. Yoshihara, PhD (13C-carbon project
leader), V. Klinke (medical student,
doctoral thesis), C. Bongard (medical
student, master thesis), P. Chevre
(chief CMR technician), and F. Recor-don
and N. Lauriers (research
nurses).
Acknowledgements
The authors would like to thank all
the members of the team of MR tech-nologists
at the CHUV for their highly
valuable participation, helpfulness
and support during the daily clinical
CMR examinations and with the
research protocols. Finally, a very
important acknowledgment goes to
Dr. Michael Zenge, Ms. Michaela
Schmidt, and the whole Siemens MR
Cardio team of Edgar Müller in
Erlangen.
3 McMurray JJV, Adamopoulos S, Anker SD,
Auricchio A, Böhm M, Dickstein K, Falk V,
Filippatos G, Fonseca C, Sanchez MAG,
Jaarsma T, Køber L, Lip GYH, Maggioni
AP, Parkhomenko A, Pieske BM, Popescu
BA, Rønnevik PK, Rutten FH, Schwitter J,
Seferovic P, Stepinska J, Trindade PT,
Voors AA, Zannad F, Zeiher A. ESC Guide-lines
for the diagnosis and treatment of
acute and chronic heart failure 2012.
European Heart Journal. 2012 May 19,
2012(33):1787–847.
4 Zannad F, McMurray JJV, Krum H,
van Veldhuisen DJ, Swedberg K, Shi H,
Vincent J, Pocock SJ, Pitt B. Eplerenone
in Patients with Systolic Heart Failure
and Mild Symptoms. New England
Journal of Medicine. 2011;364(1):11-21.
5 Gharib MI, Burnett AK. Chemotherapy-induced
cardiotoxicity: current practice
and prospects of prophylaxis. European
Journal of Heart Failure. 2002 June 1,
2002;4(3):235-42.
6 Bardy GH, Lee KL, Mark DB, Poole JE,
Packer DL, Boineau R, Domanski M,
Troutman C, Anderson J, Johnson G,
McNulty SE, Clapp-Channing N, Davidson-
Ray LD, Fraulo ES, Fishbein DP, Luceri
RM, Ip JH. Amiodarone or an Implantable
Cardioverter–Defibrillator for Congestive
Heart Failure. New England Journal of
Medicine. 2005;352(3):225-37.
7 Schwitter J. CMR-Update. 2. Edition ed.
Lausanne, Switzerland. www.herz-mri.ch.
8 Klinke V, Muzzarelli S, Lauriers N,
Locca D, Vincenti G, Monney P, Lu C,
Nothnagel D, Pilz G, Lombardi M,
van Rossum A, Wagner A, Bruder O,
Mahrholdt H, Schwitter J. Quality
assessment of cardiovascular magnetic
resonance in the setting of the European
CMR registry: description and validation
of standardized criteria. Journal of
Cardiovascular Magnetic Resonance.
2013;15(1):55.
9 Bruder O, Wagner A, Lombardi M,
Schwitter J, van Rossum A, Pilz G,
Nothnagel D, Steen H, Petersen S,
Nagel E, Prasad S, Schumm J, Greulich S,
Cagnolo A, Monney P, Deluigi C, Dill T,
Frank H, Sabin G, Schneider S,
Mahrholdt H. European Cardiovascular
Magnetic Resonance (EuroCMR)
registry-multi national results from 57
centers in 15 countries. J Cardiovasc
Magn Reson. 2013;15:1-9.
10 Lustig M, Donoho D, Pauly JM. Sparse
MRI: The application of compressed
sensing for rapid MR imaging. Magnetic
Resonance in Medicine.
2007;58(6):1182-95.
Accelerated Segmented Cine TrueFISP
of the Heart on a 1.5T MAGNETOM Aera
Using k-t-sparse SENSE
Maria Carr1; Bruce Spottiswoode2; Bradley Allen1; Michaela Schmidt2; Mariappan Nadar4; Qiu Wang4;
Jeremy Collins1; James Carr1; Michael Zenge2
1 Northwestern University, Feinberg School of Medicine, Chicago, IL, USA
2 Siemens Healthcare
3 Siemens Corporate Technology, Princeton, United States
Introduction
Cine MRI of the heart is widely
regarded as the gold standard for
assessment of left ventricular volume
and myocardial mass and is increas-ingly
utilized for assessment of car-diac
anatomy and pathology as part
of clinical routine. Conventional cine
imaging approaches typically require
1 slice per breath-hold, resulting in
lengthy protocols for complete cardiac
coverage. Parallel imaging allows
some shortening of the acquisition
time, such that 2–3 slices can be
acquired in a single breath-hold. In
cardiac cine imaging artifacts become
more prevalent with increasing accel-eration
factor. This will negatively
impact the diagnostic utility of the
images and may reduce accuracy of
quantitative measurements. However,
regularized iterative reconstruction
techniques can be used to consider-ably
improve the images obtained
from highly undersampled data. In
this work, L1-regularized iterative
SENSE as proposed in [1] was applied
to reconstruct under-sampled k-space
data. This technique* takes advan-tage
of the de-noising characteristics
of Wavelet regularization and prom-ises
to very effectively suppress sub-sampling
artifacts. This may allow for
high acceleration factors to be used,
while diagnostic image quality is
preserved.
The purpose of this study was to
compare segmented cine TrueFISP
images from a group of volunteers
and patients using three acceleration
and reconstruction approaches: iPAT
factor 2 with conventional recon-struction;
T-PAT factor 4 with conven-
tional reconstruction; and T-PAT factor
4 with iterative k-t-sparse SENSE
reconstruction.
Technique
Cardiac MRI seems to be particularly
well suited to benefit from a group of
novel image reconstruction methods
known as compressed sensing [2]
which promise to significantly speed
up data acquisition. Compressed
sensing methods were introduced to
MR imaging [3, 4] just a few years
ago and have since been successfully
combined with parallel imaging [5,
6]. Such methods try to utilize the
* Work in progress: The product is still
under
development and not commercially
available yet. Its future availability cannot
be ensured.
Table 1: MRI conventional and iterative imaging parameters
Parameters Conventional iPAT 2 Conventional T-PAT 4 Iterative T-PAT 4
Iterative recon No No Yes
Parallel imaging iPAT2 (GRAPPA) TPAT4 TPAT4
TR/TE (ms) 3.2 / 1.6 3.2 / 1.6 3.2 / 1.6
Flip angle (degrees) 70 70 70
Pixel size (mm2) 1.9 × 1.9 1.9 × 1.9 1.9 × 1.9
Slice thickness (mm) 8 8 8
Temp. res. (msec) 38 38 38
Acq. time (sec) 7 3.2 3.2
Clinical Cardiovascular Imaging
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Cardiovascular Imaging Technology
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![As outlined by Liu et al. in [1], the
image reconstruction can be formu-lated
as an unconstrained optimization
problem. In the current implementa-tion,
this optimization is solved using
a Nesterov-type algorithm [7]. The
L1-regularization with a redundant
Haar transform is efficiently solved
using a Dykstra-type algorithm [8].
This allowed a smooth integration into
the current MAGNETOM platform and,
therefore, facilitates a broad clinical
evaluation.
Materials and methods
Nine healthy human volunteers
(57.4 male/56.7 female) and
20 patients (54.4 male/40.0 female)
with suspected cardiac disease were
scanned on a 1.5T MAGNETOM Aera
system under an approved institutional
review board protocol. All nine volun-teers
and 16 patients were imaged
using segmented cine TrueFISP
sequences with conventional GRAPPA
factor 2 acceleration (conventional
iPAT 2) T-PAT factor 4 acceleration
(conventional T-PAT 4), and T-PAT factor
4 acceleration with iterative k-t-sparse
SENSE reconstruction (iterative
T-PAT 4). The remaining 4 patients
were scanned using only conventional
iPAT 2 and iterative T-PAT 4 techniques.
Note that the iterative technique is
fully integrated into the standard
reconstruction environment.
The imaging parameters for each
imaging sequence are provided in
Table 1. All three sequences were run
in 3 chamber and 4 chamber views,
as well as a stack of short axis slices.
Quantitative analysis was performed
on all volunteer data sets at a syngo
MultiModality Workplace (Leonardo)
using Argus post-processing software
(Siemens Healthcare, Erlangen,
Germany)
by an experienced cardio-vascular
MRI technician. Ejection frac-tion,
end-diastolic volume, end-systolic
volume, stroke volume, cardiac
out-put,
and myocardial mass were calcu-lated.
In all volunteers and patients,
5
4
3
2
1
blinded qualitative scoring was per-formed
by a radiologist using a 5 point
Likert scale to assess overall image
quality (1 – non diagnostic; 2 – poor;
3 – fair; 4 – good; 5 – excellent).
Images were also scored for artifact
and noise (1 – severe; 2 – moderate;
3 – mild; 4 – trace; 5 – none).
All continuous variables were com-pared
between groups using an
unpaired t-test, while ordinal qualita-tive
variables were compared using
a Wilcoxon signed-rank test.
Results
All images were acquired successfully
and image quality was of diagnostic
quality in all cases. The average scan
time per slice for conventional iPAT 2,
conventional T-PAT 4 and iterative
T-PAT 4 were for patients 7.7 ± 1.5 sec,
5.6 ± 1.5 sec and 2.9 ± 1.5 sec and
for the volunteers 9.8 ± 1.5 sec, 3.2 ±
1.5 sec and 3.0 ± 1.5 sec, respectively.
The results in scan time are illustrated
in Figure 1. In both patients and volun-teers,
conventional iPAT 2 were signifi-cantly
longer than both conventional
T-PAT 4 and iterative T-PAT 4 techniques
(p < 0.001 for each group).
The results for ejection fraction (EF)
for all three imaging techniques are
provided in Figure 2. The average EF
for conventional T-PAT 4 was slightly
lower than that measured for con-ventional
iPAT 2 and iterative T-PAT,
but the group size is relatively small
(9 subjects) and this difference was
not significant (p = 0.34 and p = 0.22
respectively).There was no statisti-cally
significant difference in ejection
fraction between the conventional
iPAT 2 and the iterative T-PAT 4
sequences (p = 0.48).
The results for image quality, noise
and artifact are provided in Figure 3.
The iterative T-PAT 4 images had com-parable
image quality, noise and arti-fact
scores compared to the conven-tional
iPAT 2 images. The conventional
T-PAT 4 images had lower image qual-ity,
more artifacts and higher noise
compared to the other techniques.
Figures 4 and 5 show an example of
4-chamber and mid-short axis images
from all three techniques in a patient
with basal septal hypertrophy. In both
series’, the conventional iPAT 2 and
iterative T-PAT 4 images are compara-ble
in quality, while the conventional
T-PAT 4 image is visibly noisier.
Cardiovascular Imaging Technology
Discussion
This study compares a novel acceler-ated
segmented cine TrueFISP tech-nique
to conventional iPAT 2 cine
TrueFISP and T-PAT 4 cine TrueFISP in
a cohort of normal subjects and
patients. The iterative reconstruction
technique provided comparable mea-surements
of ejection fraction to the
clinical gold standard (conventional
iPAT 2). The accelerated segmented
cine TrueFISP with T-PAT 4, which
was used as comparison technique,
produced slightly lower EF values
compared to the other techniques,
although this was not found to be
statistically significant. The iterative
reconstruction produced comparable
image quality, noise and artifact
scores to the conventional reconstruc-tion
using iPAT 2. The conventional
T-PAT 4 technique had lower image
quality and higher noise scores com-pared
to the other two techniques.
The iterative T-PAT 4 segmented cine
technique allows for greater than
50% reduction in acquisition time for
comparable image quality and spatial
resolution as the clinically used iPAT 2
cine TrueFISP technique. This itera-tive
technique could be extended to
permit complete heart coverage in
a single breath-hold thus greatly sim-plifying
and shortening routine clini-cal
cardiac MRI protocols, which has
been one of the biggest obstacles to
wide acceptance of cardiac MRI. With
a shorter cine acquisition, additional
advanced imaging techniques, such
as perfusion and flow, can be more
readily added to patient scans within
a reasonable protocol length.
Technology Cardiovascular Imaging
12
10
8
6
4
Single slice scan time in patients and volunteers. There was a statistically
significant reduction in scan time compared to the standard iPAT2 for both
TPAT4 acceleration and iterative reconstruction TPAT4 acceleration.
1
Qualitative scores in patients and volunteers. Image quality was highest and
noise and artifact were lowest with iterative T-PAT 4 and conventional iPAT 2
compared to conventional T-PAT 4.
3
full potential of image compression
during the acquisition of raw input
data. In the case of highly subsam-pled
input data, a non-linear iterative
optimization avoids sub-sampling
artifacts during the process of image
reconstruction. The resulting images
represent the best solution consis-tent
with the input data, which have
a sparse representation in a specific
transform domain. In the most favor-able
case, residual artifacts are not
visibly perceptible or are diagnosti-cally
irrelevant.
0
Conventional iPAT 2
Scan Time (sec)
Conventional T-PAT 4 Iterative T-PAT 4
2
Standard iPAT 2 T-PAT 4 Acceleration Iterative Reconstruction T-PAT 4 Accel.
0
Quality Noise Artifact
1 3
65,00
60,00
55,00
50,00
45,00
40,00
Ejection fraction in volunteers. Quantitatively measured ejection fractions
were comparable across all three techniques.
2
Conventional iPAT 2
Ejection Fraction (%)
Conventional T-PAT 4 Iterative T-PAT 4
2
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![Technology Cardiovascular Imaging Cardiovascular Imaging Technology
There are currently some limitations
to the technique. Firstly, the use of
SENSE implies that aliasing artifacts
can occur if the field-of-view is
smaller than the subject, which is
sometimes difficult to avoid in the
short axis orientation. But a solution
to this is promised to be part of a
future release of the current proto-type.
Secondly, the image reconstruc-tion
times of the current implemen-tation
seems to be prohibitive for
routine clinical use. However,
we anticipate future algorithmic
6A 6B
6 Real-time cine TrueFISP T-PAT 6 images reconstructed using (6A) conventional, and (6B) iterative techniques.
Contact
Maria Carr, RT (CT)(MR)
CV Research Technologist
Department of Radiology
Northwestern University
Feinberg School of Medicine
737 N. Michigan Ave.
Suite 1600
Chicago, IL 60611
USA
Phone: +1 312-926-5292
m-carr@northwestern.edu
References
1 Liu J, Rapin J, Chang TC, Lefebvre A,
Zenge M, Mueller E, Nadar MS. Dynamic
cardiac MRI reconstruction with
weighted redundant Haar wavelets. In
Proceedings of the 20th Annual Meeting
of ISMRM, Melbourne, Australia, 2002.
p 4249.
2 Candes EJ, Wakin MB. An Introduction
to compressive sampling. IEEE Signal
Processing Magazine 2008. 25(2):21-30.
doi: 10.1109/MSP.2007.914731.
improvements with increased compu-tational
power to reduce the recon-struction
time to clinically acceptable
values.
Of course, iterative reconstruction
techniques are not just limited to
cine imaging of the heart. Future
work may see this technique applied
to time intense techniques such as
4D flow phase contrast MRI and 3D
coronary MR angiography, making
them more clinically applicable.
Furthermore, higher acceleration
rates might be achieved by using an
incoherent sampling pattern [9].
With sufficiently high acceleration, the
technique can also be used effectively
for real time cine cardiac imaging in
patients with breath-holding difficul-ties
or arrhythmia. Figure 6 shows that
real-time acquisition with T-PAT 6 and
k-t iterative reconstruction still results
in excellent image quality.
In conclusion, cine TrueFISP of the
heart with inline k-t-sparse iterative
reconstruction is a promising tech-nique
for obtaining high quality cine
images at a fraction of the scan time
compared to conventional techniques.
Acknowledgement
The authors would like to thank Judy
Wood, Manger of the MRI Department
at Northwestern Memorial Hospital,
for her continued support and collabo-ration
with our ongoing research
through the years. Secondly, we would
like to thank the magnificent Cardio-vascular
Technologist’s Cheryl Jarvis,
Tinu John, Paul Magarity, Scott Luster
for their patience and dedication to
research. Finally, the Resource Coordi-nators
that help us make this possible
Irene Lekkas, Melissa Niemczura and
Paulino San Pedro.
3 Block KT, Uecker M, Frahm J. Unders-ampled
Radial MRI with Multiple Coils.
Iterative Image Reconstruction Using a
Total Variation Constraint. Magn Reson
Med 2007. 57(6):1086-98.
4 Lustig M, Donoho D, Pauly JM. Sparse
MRI: The application of compressed
sensing for rapid MR imaging. Magn
Reson Med 2007. 58(6):1182-95.
5 Liang D, Liu B, Wang J, Ying L. Acceler-ating
SENSE using compressed sensing.
Magn Reson Med 2009. 62(6):154-84.
doi: 10.1002/mrm.22161.
6 Lustig M, Pauly, JM. SPIRiT: Iterative
self-
consistent parallel imaging
reconstruction from arbitrary k-space.
Magn Reson Med 2010. 64(2):457-71.
doi: 10.1002/mrm.22428.
7 Beck A, Teboulle M. A fast iterative
shrinkage-thresholding algorithm for
linear inverse problems. SIAM J Imaging
Sciences 2009. 2(1): 183-202.
8 Dykstra RL. An algorithm for restricted
least squares regression. J Amer Stat
Assoc 1983 78(384):837-842.
9 Schmidt M, Ekinci O, Liu J, Lefebvre A,
Nadar MS, Mueller E, Zenge MO. Novel
highly accelerated real-time CINE-MRI
featuring compressed sensing with k-t
regularization in comparison to TSENSE
segmented and real-time Cine imaging.
J Cardiovasc Magn Reson 2013.
15(Suppl 1):P36.
4A 4B 4C
Four chamber cine TrueFISP from a normal volunteer. (4A) Conventional iPAT 2, acquisition time 8 s. (4B) Conventional
T-PAT 4, acquisition time 3 seconds. (4C) Iterative T-PAT 4, acquisition time 3 seconds.
4
5A 5B 5C
End-systolic short axis cine TrueFISP images from a patient with a history of myocardial infarction. A metal artifact from a previous
sternotomy is noted in the sternum. There is wall thinning in the inferolateral wall with akinesia on cine views, consistent with
an old infarct in the circumflex territory. (5A) Conventional iPAT 2, (5B) conventional T-PAT 4, (5C) iterative T-PAT 4.
5
30 MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world Reprinted from MAGNETOM Flash 5/2013 Reprinted from MAGNETOM Flash 5/2013
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![Combined 18F-FDG PET and MRI Evaluation
of a case of Hypertrophic Cardiomyopathy
Using Simultaneous MR-PET
Ihn-ho Cho, M.D.; Eun-jung Kong, M.D.
Department of Nuclear Medicine, Yeungnam University Hospital, Daegu, South Korea
Introduction
Hypertrophic cardiomyopathy (HCM)
is a common condition causing left
ventricular outflow obstruction, as
well as cardiac arrhythmias. Cardiac
MRI is a key modality for evaluation
of HCM. Apart from estimating left
ventricular (LV) wall thickness, LV
function and aortic flow, MRI is capa-ble
of estimating the late gadolinium
enhancement in affected myocardium,
which has been shown to have a
direct correlation with incidence and
Patient history
A 25-year-old man presented to the
cardiology department with inciden-tal
ECG abnormality after fractures to
his left 2nd and 4th fingers. Although
he had not consulted a doctor, he had
been suffering from mild dyspnea
with chest discomfort at rest and
exacerbation at exercise since May
2012. Echocardiography revealed
non-obstructive hypertrophic cardio-myopathy
(Maron III) with trivial MR.
The patient was referred for a simul-taneous
MR-PET study for 18F-FDG
PET and cardiac MRI with Gadolinium
(Gd) contrast for evaluation of the
morphological and metabolic status
of the hypertrophic myocardium.
The patient was injected with 10 mCi
18F- FDG following glucose loading.
Simultaneous MR-PET study per-formed
on a Biograph mMR was
started one hour following tracer
injection. Following standard Dixon
sequence acquisition for attenuation
correction, the comprehensive car-diac
MRI sequences were acquired
including MR perfusion after Gd con-trast
infusion, as well as post contrast
late Gd enhancement studies. Static
18F-FDG PET was acquired simultane-ously
during the MRI acquisition.
Cardiovascular Imaging Clinical
2A 2
Discussion
The late Gd enhancement within
the hypertrophic septum along with
the non-uniform glucose metabolism
demonstrated by the patchy 18F-FDG
uptake within the hypertrophic septum
exactly corresponding to the area of
Gd enhancement reflect myocardial
fibrosis within the asymmetric septal
hypertrophy. Myocardial fibrosis and
the presence of late Gd enhancement
on MRI has been shown to be associ-ated
with increased risk of cardiac
arrhythmia [1] as evident from the
symptoms of this patient.
severity of arrhythmias in HCM [1].
In patients with HCM, late gadolinium
enhancement (LGE) on CE-MRI is pre-sumed
to represent intramyocardial
fibrosis. PET myocardial perfusion
studies have shown slight impairment
of myocardial blood flow with phar-macological
stress in hypertrophic
myocardium in HCM, presumably
related to microvascular disease [2].
18F-FDG PET has been sporadically
studied in HCM, mostly for evalua-tion
of the metabolic status of the
hypertrophic myocardial segment, espe-cially
after interventions such as trans-coronary
ablation of septal hypertro-phy
(TASH) [3] or to demonstrate
partial myocardial fibrosis [4]. This
clinical example illustrates the value of
integrated simultaneous 18F-FDG PET
and MRI acquisition performed on the
Biograph
mMR system.
1A 1B
Short-axis views of end diastole and end systole at 3 different sections in the left ventricle obtained from gated TrueFISP cine
MRI acquisitions performed on Biograph mMR. Note the thick hypertrophic septum (white arrow), which demonstrates the
degree of asymmetric septal hypertrophy.
1
1D
1F
1C
1E
1G
1
1
End Diastole End Systole
2
3
2
3
Simultaneous MR-PET acquisition
provides combined acquisition of
both modalities, thereby ensuring
accurate fusion between morphologi-cal
and functional images due to
simultaneous PET acquisition for every
MR sequence. The exact coregistra-tion
of the patchy 18F-FDG uptake
in the area of Gd enhancement within
the hypertrophic upper septum
reflects the advantage of simultane-ous
acquisition.
End diastolic
and end
systolic views
of 2-chamber
and 4-chamber
views obtained
from gated cine
TrueFISP acqui-sitions
showing
thickness of
the asymmetric
septal hyper-trophy
(white
arrow).
2C
2B
2D
End Diastole
4-chamber view 2-chamber view
End Systole
3
3
Static 18F-FDG
PET images
in short-axis,
horizontal
long-axis and
vertical long-axis
views
demonstrating
normal uptake
in the LV
myocardium
except the
non-uniform
uptake pattern
in the hypertro-phied
septum
(white arrows).
LV cavity size
appears normal.
MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world 33
Clinical Cardiovascular Imaging
32 MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world Reprinted from MAGNETOM Flash 5/2013 Reprinted from MAGNETOM Flash 5/2013](https://image.slidesharecdn.com/magnetomflash56scmr-01331257-140821155659-phpapp02/85/SCMR-Edition-Issue-56-17-320.jpg)
![Clinical Cardiovascular Imaging Further Reading
4
5
Contact
Ihn-ho Cho, M.D.
Department of Nuclear Medicine
Yeungnam University
College of Medicine
Daegu Hyunchungro 170
South Korea
nuclear126@ynu.ac.kr
4D
T2 HASTE T2 STIR T1 FAT SAT
4B
4E
References
1 Rubinstein et al. Characteristics and
Clinical Significance of Late Gadolinium
Enhancement by Contrast-Enhanced
Magnetic Resonance Imaging in Patients
With Hypertrophic Cardiomyopathy.
Circ Heart Fail. 2010;3:51-58.
2 Bravo et al. PET/CT Assessment of
Symptomatic Individuals with Obstructive
and Nonobstructive Hypertrophic Cardio-myopathy.
J Nucl Med 2012; 53:407–414.
Transverse, short-axis and
vertical long-axis MR and
fused MR-PET images show
hypertrophied septum
(white arrows) and normal
thickness of rest of left
ventricular myocardium
with corresponding
normal 18F-FDG uptake.
The T2-weighted STIR (fat
suppression) image shows
slight hyperintensity in
the middle of the hypertrophied
septum which
shows corresponding
non-uniformity in 18F-FDG
uptake.
Post-contrast MR short-axis
images demonstrate late Gd
enhancement within the
hypertrophied septum
(white arrow), which shows
corresponding non-uniform
patchy uptake of 18F-FDG.
4A
5A 5B
4C
4F
4 Funabashi N et al. Partial myocardial
fibrosis in hypertrophic cardiomyopathy
demonstrated by 18F-fluoro-deoxy-glucose
positron emission tomography
and multislice computed tomography.
Int J Cardiol. 2006 Feb 15;107(2):284-6.
3 Kuhn et al. Changes in the left ventricular
outflow tract after transcoronary
ablation of septal hypertrophy (TASH)
for hypertrophic obstructive cardiomy-opathy
as assessed by transoesophageal
echocardiography and by measuring
myocardial glucose utilization and.
perfusion. European Heart Journal
(1999) 20, 1808–1817.
34 MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world
Cardiac MRI at 3T:
An Indian Experience of 80 Cases
Cardiac MRI at 3T: An Indian Experience
of 80 Cases of Cardiac MRI with Review
of Literature
Kalashree A. Bidarkar DNB; Nikhil Kamat, M.D., DMRD, DNB; M. L. Rokade, M.D., DNB; Nitin Burkule, M.D., DM;
Shubra Gupta
Departments of Radiology and Cardiology, Jupiter Hospital, Thane, Maharashtra, India
Diagram 1 [7]: A schematic representation
of three zones of affection in case of an MI:
Clinical Cardiology Cardiology Clinical
3
3A, B, 4C, 2C views reveal
moderate dilated LA and LV with
thinning of LV anterior wall,
interventricular regions and the
apex. Aneurysmal dilatation of
the thinned apex is seen (thin
yellow arrows).
Figure 4 demonstrates CMR findings in
acute myocardial infarction, seen as
edema on T2-weighted images and
perfusion defect (microvascular
obstruction) on the post-contrast PSIR
images.
B) Pericardium
MRI is particularly suitable for eval-uation
of pericardial inflammation,
evaluation of small or loculated
pericardial effusions, functional
abnormalities caused by pericardial
constriction, and for characteriza-tion
of pericardial masses [19].
1A
Clinical Cardiology Cardiology Clinical
7
The diagnosis of constrictive peri-carditis
is greatly aided by excellent
depiction of pericardium at MR
imaging. Normal pericardium is less
than 3 mm thick. Pericardial thick-ness
of 4 mm or more indicates
abnormal thickening, and when
accompanied by clinical signs of
heart failure is highly suggestive 2A
of
constrictive pericarditis [10]. Peri-cardial
thickening may be limited to
the right side of the heart or even
a smaller area such as the right
atrio-ventricular groove.
In chronic constrictive pericarditis
there is typically bi-atrial enlarge-ment.
35-year-old male patient on treatment for pulmonary Koch’s disease, presented
with dyspnoea.
(5A, B) Horizontal long axis black and white blood images reveal thickened
pericardium (6 mm).
(5C, D) Post-contrast images acquired 15 minutes post Gd administration reveal
diffuse pericardial enhancement consistent with the diagnosis of constrictive
pericarditis.
5
1B
Clinical Cardiology Cardiology Clinical
Also, the central cardiovascu-lar
2B
structures show a characteristic
morphology with the right ventricle
showing a narrow tubular configu-ration
[10].
Cine images are useful to judge
the pathophysiologic consequence
of pericardial thickening and the
‘Diastolic Septal bounce’ [7].
Diastolic septal bounce is a hemo-dynamic
hallmark of ventricular
constriction seen due to increased
interventricular dependence and
demonstrated as abnormal ventric-ular
septal
6A 6B
32-year-old male patient with a history of sudden atrial fibrillation was evaluated by CMR.
(9A, B) SSFP sequential 3-chamber SSFP cine MR images in the diastolic and mid-systolic phases respectively reveal LV hyper-trophy
(7C, D) PSIR images acquired
15 minutes post Gd administration
reveal patchy transmural LGE in
the thickened IV septum and RV
insertion sites, suggestive of
scarred tissue (solid white arrows).
Clinical Cardiology Cardiology Clinical
8
21-year-old male patient with
complaints of progressive dyspnoea
since childhood was referred for CMR.
(12A, B) SSFP 4- and 2-chamber views
reveal moderate cardiomegaly.
Clinical Cardiology Cardiology Clinical
15
46-year-old asymptomatic male patient
with a family history of sudden cardiac
deaths came to our institution for CMR
evaluation.
(15A, B) SSFP short axis images reveal
severe non-compaction of the apex, mid
lateral and mid anterior walls with a ratio
of NC/C being 2.7 suggestive of
non-compaction CMP. Left atrial
dilatation was also observed.
Figures 15, 16 demonstrate the imag-ing
characteristics in non-compaction
CMP.
Cardiac masses
CMR is widely recognised as the imag-ing
modality of choice in evaluation of
cardiac masses. Invasion in to adjacent
structures, precise compartmental
localisation can be easily accomplished
narrowing the differential diagnosis [9].
1) Thrombus: a common differential
diagnosis for cardiac tumors is
intracardiac thrombus.
Thrombi may appear isointense or
slightly hyperintense relative to
the myocardium on black blood pre-pared
MRI enables differentia-tion
between thrombus and
surrounding myocardium as throm-bus
being avascular is character-ized
by lack of contrast uptake.
Rarely, large chronic thrombi may
show peripheral enhancement and
be diagnostically challenging [17].
Figure 17 shows a case of a
patient suspected to have a LV clot
(on echocardiography), confirmed
on CMR.
2) Cardiac myxomas: These account
Their contours are round or oval,
sometimes lobulated with a smooth
surface and a narrow pedicle. They
have a gelatinous structure and
may be relatively high in signal on
SSFP and static images. They typi-cally
demonstrate heterogeneous
enhancement on delayed-enhance-ment
images [9] (Fig. 18).
We encountered one patient
referred for a CMR for assessment
of a mass attached to the inter-ventricular
septum (as seen on
echocardiography). Although the
location was uncommon, the mass
showed morphologic and enhance-ment
Table 1:
MR sequencing
Anatomy HASTE 2D
Function
Cine SSFP
(2CV,4CV,SA)
Morphology
T1-weighted
(2CV,4CV,SA)
STIR dark blood
(2CV,4CV,SA)
Fluid content
T2-weighted
(2CV,4CV,SA)
Gadolinium
kinetics
TI scout baseline
Delayed
enhancement
IR turbo TrueFISP
2D
Abbreviations: 2D, 2 dimensional ; CV,
chamber view; IR, inversion recovery; SA,
short axis; TI, inversion time; STIR, Short TI
Inversion Recovery; TSE, turbo spin echo
Table 2: Special
considerations
Acute MI
T2-weighted or
STIR dark blood
Cardiac mass
or thrombus
TSE dark blood
T1, TSE dark
blood T2 fat sat
Clinical Cardiology Cardiology Clinical
18
for 20–25% of cardiac tumors. The
most common locations are in the
left atrium (60–75%), right atrium
(20–28%), but rarely in both the
atria and ventricles [17].
characteristics of a myxoma
and was diagnosed as such.
17
LV clots in a 65-year-old male patient with
dyspnoea.
(17A, B) PSIR images acquired 15 minutes
post Gd administration reveal transmural
LGE in the apex and the anteroseptal wall
suggestive of non-viable myocardium in the
LAD. A layered non-enhancing clot is seen
at the apex adjacent to the akinetic apical
myocardium (thin yellow arrows).
20 Figure 21A: Shows ventricular septal defect (arrow).
22
14A 14B 14C
HASTE images [21] .Contrast-enhanced
19
(15C, D) PSIR images acquired 15
minutes after Gd administration showed
moderate patchy LGE involving the
anterior wall and interventricular
septum, predominantly at the RV
insertion sites (asterisk in C).
16
Another case of non-compaction CMP in
a 28-year-old post-partum female with
mild dyspnoea on exertion.
(16A, B) SSFP 4-chamber view and short
axis images reveal moderate cardio-megaly
with non-compaction seen along
the lateral, inferior and posterior walls
and the apex (white solid arrows).
18
55-year-old male patient with a history
of recurrent TIAs for CMR evaluation.
(18A, B) SSFP 4-chamber and short axis
views reveal a nodular soft tissue mass
adherent to the IV septum (solid white
arrows).
13
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MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world 35
Cardiac MRI is the main investigation
modality for a wide range of clinical
applications and has emerged as a
virtual ‘one-stop-shop’ for imaging
conditions such as Cardiomyopathies.
CMR has added uniquely to the
methods for non-invasive assessment
of myocardial viability by a combina-tion
of cine imaging and delayed
hyper-enhancement. CMR provides
excellent depiction of pericardium
in conditions such as pericarditis,
Read the comprehensive article
www.siemens.com/
magnetom-world
pericardial effusions, and masses.
It provides optimal assessment of the
location, functional characteristics,
and soft tissue features of cardiac
tumors, allowing accurate differen-tiation
of benign and malignant
lesions.
MRI is ideally suited to serve as the
primary imaging modality in patients
with congenital heart disease due its
non-invasive and biologically harm-less
nature, and its ability to provide
accurate anatomical and functional
information. Several investigators have
confirmed the SNR advantages of CMR
at 3T. These indicate an overall quan-titative
improvement in SNR and CNR,
thus improving imaging capabilities.
Dr. Bidarkar and colleagues (Depart-ments
of Radiology and Cardiology,
Jupiter Hospital, Thane, Maharashtra,
India) illustrate 80 cases of cardiac MRI
imaged between January 2012 and
August 2013 on a 3T MAGNETOM Verio.
Contrast-enhanced study
of the LV myxoma.
(18E, F) PSIR images
acquired 5 minutes and
15 minutes post Gd adminis-tration
reveal minimal to no
enhancement in the 5 min
scan and intense homog-enous
enhancement in the
delayed scan (solid white
arrows).
Congenital heart diseases
Congenital heart disease is a com-mon
clinical entity and occurs in
0.8% of newborns [23]. Major
advances in hardware design, new
pulse sequences, and faster image
reconstruction techniques allow
rapid high resolution imaging of
complex cardiovascular anatomy and
physiology [24].
In our study, we imaged one 9-year-old
male patient with complaints of
progressive dyspnoea. Since contact
of patients with CHDs referred for
cardiac MRI exam is limited, we frag-mented
a single case of complicated
CHD to demonstrate various cardiac
anomalies.
The CMR study demonstrated the
following cardiac anomalies:
• Ventricular septal defect: A com-mon
congenital heart disease clas-sified
into membranous, muscular,
endocardial cushion defects, and
conal [23] (Fig. 21A).
• Atroial septal defect: The main
types of ASD are secundum (middle
of atrial septum) as seen in figure
21B, sinus venosus (at junction of
SVC and right atrium superiorly),
and primum (near the AV valves)
[23].
• Patent ductus arteriosus: PDA is the
persistence of the 6th aortic arch
and accounts for 10% of congenital
heart disease. MRI demonstrates a
persistent connection between the
origin of left pulmonary artery to
the descending aorta just beyond
origin of the left subclavian artery
[23] as seen in figure 22.
• Transposition of great arteries: The
most common congenital heart
lesion found in neonates, found in
5–7% of congenital cardiac malfor-mations.
Congenitally-corrected
transposition refers atrioventricular
discordance, ventricular inversion
transposition, and inversion of great
arteries [25] (Fig. 19).
Also observed in the same patient was
situs inversus as shown in figure 20.
Limitations
A few technical limitations we encoun-tered
during our study on a 3T MRI were:
• Inability to achieve optimal myocar-dial
nulling: Optimal TI scout was not
obtained in three of our patients
despite repeated attempts
• Exaggerated flow artifacts: Flow arti-facts
seemed to be more pronounced
in areas of turbulent blood flow.
These technical issues have been for-warded
to the Siemens application
team and are currently under review.
The team has in the past overcome
many technical challenges of cardiac
Coronal T2-weighted
image shows liver situated
on left side of the
abdomen – situs inversus.
(21B) Shows atrial septal defect, secundum type (arrow).
21
(22A, B) Demonstrate
persistent ductus arteriosus
(PDA) connecting aorta to
pulmonary artery.
MRI on 3T due to high gradient factors
in comparison with 1.5T, and opti-mized
the protocol of cardiac MRI on
3T. With this experience, the team
appears confident of being able to pro-vide
a solution to these limitations in
the near future.
Conclusion
Cardiac MRI forms a mainstay investi-gation
modality for a wide range of
clinical applications and has emerged
as a virtual ‘one-stop’ for imaging
conditions like Cardiomyopathies [11].
CMR has added uniquely to the meth-ods
for non-invasive assessment of
myocardial viability by a combination
of cine imaging and delayed hyper-enhancement
(LGE).
18E 18F
Figure 19A: Shows right
sided aortic arch (asterisk).
(19B) Shows that the aorta
arises from the morpho-logical
right ventricle
(curved arrow).
19A 19B
(22C) Demonstrates multiple
aortopulmonary collaterals
(MAPCAs) (red arrows).
(22D) Shows the atretic
pulmonary trunks and main
branch pulmonary arteries
measuring 4 mm in diameter
(yellow asterisk).
20 21A 21B
22A 22B
22C 22D
15 MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world 16
15A 15B
15C 15D
16A 16B
16C 16D (16C, D) PSIR images acquired 15
minutes post Gd administration reveal
mild subendocardial LGE in the septal
region, anterior and posterior walls, not
conforming to any vascular territory
(thin yellow arrows).
17A 17B
18A 18B
18C 18D (18C, D) T1-weighted short axis and STIR
4-chamber views respectively demonstrate
the mass which appears isointense to the
myocardium on T1w and hyperintense on
STIR images (myxoid content) suggestive
of LV myxoma (solid red arrows).
NC/C ratio = 2.7
12
Example of an advanced case of
idiopathic dilated cardiomyopathy in
a 34-year-old female patient with
dyspnoea and intermittent chest
pain.
(13A, B) SSFP 4- and 2-chamber
views respectively, show dilatation of
all the cardiac chambers.
myocytes. The abnormalities seen in
primary dilated cardiomyopathies are
fairly similar to those seen as an end
result of CAD (ischemic cardiomyopa-thy)
[7]. LGE can be seen in both
entities. However, ischemic injury pro-gresses
as a wavefront from the
subendocardium to epicardium and
shows a territorial distribution (Fig. 11).
Hyper-enhancement patterns that
spare the subendocardium and are
limited to middle or epicardial portions
of the LV, are clearly in a non-CAD dis-tribution
[9] (Fig. 12).
Restrictive cardiomyopathy
Restrictive CMP is characterised by
reduced ventricular filling and diastolic
volume, leading to atrial dilatation and
venous stasis, with preserved systolic
function. Restrictive CMP may be idio-pathic,
secondary to infiltrative and
storage disorders (such as amyloidosis
and sarcoidosis) or associated with
myocardial disorders such as hypereo-sinophilic
syndrome.
Cardiac MRI is a fundamental diagnos-tic
tool because it helps in differentiat-ing
between restrictive CMP and con-strictive
pericarditis which have
different therapeutic approaches.
Although reduced ventricular filling
and diastolic volumes may be a fea-ture
of both, pericardial thickening
> 4 mm is typical of pericarditis [12]
(Fig. 5).
Cardiac MRI also helps in the differ-entiation
between the above entities
in cases with minimally thickened
pericardium. Morphologic images in
restrictive CMP may show atrial
enlargement. Cine images allow
assessment of altered diastolic ven-tricular
filling. Cine MRI assessment
of diastolic ventricular septal move-ments
and real time MRI imaging of
septal movements during respiration
show that in restrictive CMP, septal
convexity is maintained in all respira-tory
phases, whereas in constrictive
pericarditis, septal flattening can be
seen in early inspiration [12] (Fig. 6).
The issue of LGE in idiopathic restric-tive
CMP has not been specifically
addressed in the literature, although
late enhancement patterns in specific
causes of restrictive CMP have been
described [12].
Figure 14 illustrates a case of Restric-tive
CMP.
Non-compaction
cardiomyopathy
Left ventricular myocardial non com-paction
(LVNC) is a recently recog-nised
form of primary and genetic
cardiomyopathy. Also known as
spongy myocardium, LVNC is charac-terised
by prominent ventricular
myocardial trabeculations and deep
intertrabecular recesses communicat-ing
with the ventricular cavity. LVNC
is secondary to arrest in the normal
process of myocardial compaction
during fetal life.
CMR can clearly display the com-pacted
and non-compacted myocar-dium
layers better than echocardiog-raphy
[13].
In a normal ventricle, the proportion
of ventricular wall formed by trabec-ulations
never exceeds thickness of
the compacted layer. In LVNC, the
thickness of non-compact myocardium
is greater than that of compacted
layer which is thinned. It is suggested
that a NC/C ratio > 2.3 in diastole dis-tinguishes
pathological non compac-tion
from pronounced trabeculae
seen in other CMPs [13].
(12C, D) PSIR images acquired
15 minutes post Gd administration
reveal no LGE in the myocardium to
suggest fibrosis. The patient was
diagnosed as idiopathic/non ischaemic
dilated cardiomyopathy.
(13C, D) PSIR images acquired 15
minutes post Gd administration
reveal diffuse subendocardial LGE in
the septal, anterior and posterior
walls (thin yellow arrows). Mild
pericardial effusion can be appre-ciated
on the short axis view (white
solid arrow).
12A 12B
10
12C 12D
13A 13B
13C 13D
13-year-old female patient with a history of progressive dyspnoea.
(14A) SSFP images in the horizontal long axis view reveals significant bi-atrial dilatation (thin yellow arrows) with normal sized
ventricular cavities.
(14B, C) PSIR images acquired 15 minutes post Gd administration demonstrate no enhancement in the myocardium.
Findings were suggestive of restrictive cardiomyopathy.
14
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motion towards the left ventricle
in early diastole during onset of
inspiration [9]. This finding is help-ful
(double headed arrow in 9B) and LA dilatation (thin yellow arrow).
(9C) Systolic phase demonstrates anterior motion of the mitral leaflet causing obstruction at the LVOT (solid yellow arrow)
with resultant turbulent jets in the LA and at the LVOT – systolic anterior motion (SAM).
9
Preclinical HCM.
Shown are images of
a 35-year-old asympto
matic male patient
with a family history
of HCM.
(10A, B) SSFP
sequential 4-chamber
and short axis SSFP
cine MR images reveal
mid biatrial dilatation
(thin yellow arrows)
with no significant
myocardial hypertrophy
(double headed blue
arrows).
entities. Mass-like HCM more pre-cisely
parallels the homogenous
signal intensity characteristics and
perfusion of adjacent normal myo-cardium,
while tumors show hetero-geneous
signal intensity, enhance-ment,
and perfusion characteristics
that differ from those of remainder
of the left ventricle [20].
6) Pre-clinical HCM
Screening of family members of
patients with HCM is important
because first-degree relatives of
such patients have a 50% chance
of being a gene carrier.
Cardiac MRI is a useful screening
tool in patients with a normal
LV thickness who have symptoms
of HCM or in asymptomatic HCM
mutation carriers. However, dis-ease
expression can be heteroge-nous
and varied, even with the
same mutation; hence follow-up
screening needs to be considered
every 2 to 5 years, particularly in
young patients [20].
Figure 10 illustrates CMR finding s
in a 36-year-old asymptomatic
male patient with a family history
of HCM.
Dilated cardiomyopathy
(DCM)
These are a common cause of con-gestive
heart failure characterized by
fibrosis and decreased number of
CMR of a 65-year-old male patient with a history of anterior wall MI.
(11A, B) SSFP 4- and 2-chamber chamber views reveal moderately dilated left ventricle.
(11B, C) PSIR images acquired 15 minutes post Gd administration reveals transmural LGE in the antero-septal
wall, suggestive of non-viable myocardium in the LAD and RCA territories (thin yellow arrows).
The patient was diagnosed as ischaemic dilated cardiomyopathy.
11
9A 9B 9C
(10C, D) PSIR images
acquired 15 minutes
post Gd administration
reveal LGE along the
inferior and posterior
walls suggestive of
early fibrosis.
in distinguishing between con-strictive
pericarditis and restrictive
cardiomyopathy [9] (Fig. 6).
Figure 5 illustrates the characteristic
findings of thickened pericardium
and diffuse pericardial enhancement
in a case of constrictive pericarditis.
10A 10B
10C 10D
11A 11B
11C 11D
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(3B, C) PSIR images taken
15 minutes post Gd
administration reveal
transmural LGE in these
(solid white arrows) areas
suggestive of non-viable
myocardium in the LAD
territory.
C) Cardiomyopathies (CMPs)
Cardiomyopathies are chronic
progressive diseases of the myo-cardium
with often genetic /
inflammation / injury as factors
contributing to their development
[7]. Cardiac MRI has become
an important tool for the diagno-sis
and follow-up of patients with
cardiomyopathies. It has a unique
ability to differentiate between
different enhancement patterns in
diseased myocardium on inversion
recovery delayed Gadolinium-enhanced
images, making it suit-able
for evaluation of cardiomyop-athies
[18].
4
42-year-old male patient with
symptoms of acute myocardial
infarction.
(4A, B) SSFP 4-chamber and short
axis images reveal mildly thickened
interventricular septum with subtle
hyperintense areas suggestive of
post-MI edema (solid red arrows).
Hypertrophic cardiomyopathy
(HCM): A genetically-acquired
condition resulting from abnormal-ity
in the sarcomere, it results in
hypertrophy of the myocardium.
MRI has proven to be an important
tool in the evaluation of patients
with suspected HCM since it helps
readily diagnose those with phe-notypic
expression of the disorder
and potentially identify the subset
of patients at risk of sudden car-diac
deaths. MRI is also capable of
detecting regions of localised
hypertrophy that are missed by
echocardiography.
A significant percentage of patients
with HCM demonstrate LGE char-acteristically
involving regions of
hypertrophy, junctions of interven-tricular
septum and RV free wall
[9]. LGE is usually patchy and mid-wall
in location. LGE in HCM also
has a predilection for the anterior
and posterior insertion points.
An exception to this is in areas of
burnt-out myocardium where the
left ventricular wall is thinned and
enhancement is full thickness [18].
The presence of LGE denotes scar
tissue, a potential nidus for fatal
arrhythmias. CMR can be used
to follow the patients following
ventricular septal resection / percu-taneous
ablation [7].
Phenotypes of HCM
1) Asymmetric HCM
This is the most common morpho-logic
presentation of HCM, the
anteroseptal being the commonly
hypertrophied segment. Asymmet-ric
septal wall hypertrophy causes
LVOT obstruction in 20–30% of
cases.
Asymmetric / septal HCM may be
diagnosed when septal thickness
is greater than or equal to 15 mm
or when the ratio of septal thick-ness
to the thickness of inferior
wall of the left ventricle is greater
than 1.5 at the midventricular
level [20].
Abnormalities of the mitral valve
may occur due to primary abnor-mality
of the valve itself or due to
LVOT obstruction. Systolic anterior
motion of the mitral valve (SAM)
is a phenomenon in which a por-tion
of the anterior leaflet of the
mitral valve distal to the coaptation
gets displaced / pulled in to the
LVOT by venture or drag forces,
leading to transient LVOT obstruc-tion
[7] (Fig. 9). Over time, the
systolic anterior motion of the
mitral valve leads to sub-aortic
mitral impact lesion on the sep-tum
which undergoes fibrosis;
thickening of mitral leaflet and
chordae from the resultant trauma;
a posteriorly directed mitral regur-gitant
jet in to the left atrium
and a systolic gradient along the
LVOT [18].
Patients with LVOT obstruction
unresponsive to medical therapy
(5%) are candidates for surgical
myectomy or septal alcohol abla-tion
[20]. Our patient, however,
was put on medical therapy.
2) Apical HCM
The apical variant of HCM shows
an absolute apical thickness of
> 15 mm or a ratio 1.3 to 1.5. More
subjective criteria are the oblitera-tion
of LV apical cavity in systole
and failure to identify a normal pro-gressive
reduction in LV wall thick-ness
towards the apex.
The left ventricle shows a charac-teristic
‘spade-like’ configuration
on vertical long axis views.
An apical aneurysm formation
with delayed enhancement is
sometimes seen referred to as the
‘burnt-out apex’ resulting from
ischemia due to reduced capillary
density resulting in ischemic fibro-sis.
Similar appearance of ‘burnt-out
apex’ is also seen in HCM causing
mid- ventricular obstruction with
apical aneurysm formation, as
described in figure 8.
The LV apex may not be assessed
well with echocardiography leading
to false negative interpretations.
Hence cardiac MRI is strongly rec-ommended
as optimal imaging
modality for evaluation of apical
HCM [20].
3) HCM with mid-ventricular
obstruction
A variant of asymmetric HCM pre-dominantly
involving the middle
third of the left ventricle may result
in severe mid-ventricular narrowing
and obstruction. This condition may
be associated with formation of an
apical aneurysm which is thought
to result from increased generation
of systolic pressures within the apex
from the mid-ventricular obstruction
[18] (Fig. 8).
4) Symmetric HCM
This variant is encountered in about
42% of HCM cases and is character-ized
by a concentric LV hypertrophy
with a small cavity dimension and
no evidence of a secondary cause.
This entity has to be differentiated
from other causes of diffuse LV wall
thickening including athlete’s heart,
amyloidosis, sarcoidosis, Fabry’s dis-ease,
and secondary adaptive pat-tern
of LV hypertrophy due to hyper-tension
or aortic stenosis, since the
treatment strategies differ. Cardiac
MRI is known to play an important
role in differentiating other causes
of myocardial hypertrophy from HCM
because of the unique ability of DE
MRI imaging to characterize differ-ent
enhancement patterns in dis-eased
myocardium [20]. Figure 7
illustrates a case of concentric HCM
in a symptomatic patient.
5) Mass-like HCM
Mass-like HCM manifests as a mass-like
hypertrophy because of focal
segmental location of myocardial
disarray and fibrosis which may be
differentiated from neoplastic
masses. MR imaging with first pass
perfusion and DE technique helps
to differentiate between the two
Concentric HCM in a symptomatic
35-year-old male patient.
(7A, B) Short axis and vertical
long axis SSFP images show
symmetrically thickened LV walls
(arrows) with atrial dilatation.
HCM with mid-ventricular
obstruction. CMR evaluation of
a 55-year-old male patient with
a family history of sudden cardiac
deaths.
(8A, B) Horizontal long axis SSFP
cine MR images reveal significant
hypertrophy of the LV myocardium
(16–17 mm width). The thickened
myocardium (asterisk in 8A) causes
mid-cavity obstruction with apical
thinning and outpouching resulting
in a ‘dumbbell shaped LV’.
(8C, D) PSIR images acquired 15
minutes post Gd administration
show subendocardial LGE (solid
white arrows), around 50% in the
proximal areas and transmural in
the apex (burnt out apex)
suggestive of ischaemic fibrosis.
7A 7B
7C 7D
8A 8B
8C 8D
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3A 3B
(4C, D) PSIR images acquired
immediately post Gd administration
demonstrate perfusion defect in the
LAD territory corresponding to
microvascular obstruction (solid
white arrows).
3C 3D
4A 4B
4C 4D
5A 5B
5C 5D
An example of Diastolic septal bounce. Septal flattening / inversion seen in
constrictive pericarditis, since outward expansion of the right ventricle is
limited by a non-compliant pericardium.
(6A) Shows IV septum in mid systolic phase.
(6B) Diastolic phase reveals mild leftward bowing of the septum.
6
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the LAD, 10 in the RCA and 4 in
the LCX territories, corresponding to
non-viable myocardium (Table 3).
11 patients demonstrated < 50% of
myocardial LGE. Of these, 5 belonged
to LAD territory and 2 and 4 to the
LCX and RCA territories, respectively
(Table 3).
On follow up, 7 patients underwent
revascularisation procedures. All of
these reported to experience symp-tomatic
relief.
15 patients were evaluated for cardio-myopathy.
All patients with CMP are
managed by medical therapy and are
doing well.
We evaluated 2 patients for constric-tive
pericarditis. Both were started
on anti-Koch’s therapy and are symp-tomatically
better.
5 patients were referred for evalua-tion
of cardiac masses after an echo-cardiographic
study. 3 of these
had revealed a LV clot and 1 patient
had demonstrated a nodular mass
attached to the LV wall. One patient
suspected to have a mass posterior
to left atrium on echocardiography
was diagnosed with straight back
syndrome with the thoracic vertebral
body indenting the left atrium. LV
clots were confirmed on CMR and the
patients were put on anticoagulation
therapy.
One patient diagnosed as LV myxoma
being managed on medical therapy,
is doing well.
Discussion
A) Myocardial viability
Ischemic heart disease (IHD) is
today one of the leading causes of
death all over the world. Cardiac
MRI plays an important role com-plementary
to other imaging
modalities in evaluation of patients
with IHD. Myocardial infarction
results from rupture of an athero-sclerotic
plaque in a coronary artery
leading to thrombus formation.
The subendocardium is most vul-nerable
to ischemia and an infarct
expands form subendocardium
to subepicardium [7].
Myocardial infarction, scarring and
viability are simultaneously exam-ined
using technique of delayed
enhancement MRI.
Delayed / late gadolinium hyper-enhancement
is caused by delayed
washout of contrast agent from
the myocardium. Delayed
enhancement is performed 10–15
minutes after i.v. administration of
0.15 to 0.2 mmol/kg of gadolinium.
An inversion recovery sequence is
used in which normal myocardium
is nulled to accentuate the delayed
enhancement [7].
Both acute and chronic infarctions
enhance. In acute infarctions, con-trast
enters the damaged myocar-dial
cells due to membrane disrup-tion
(microvascular obstruction /
no reflow zones). These regions are
recognised as dark central areas
surrounded by hyperenhanced
necrotic myocardium. This finding
indicates the presence of damaged
microvasculature in the core of an
area of infarction. The presence of
a ‘no-reflow’ zone appears to be
associated with worse LV remodel-ling
and outcome [7, 9]. CMR can
be safely carried out in patients
with acute MI and primary angio-plasty
and aids in risk stratification.
T2-weighted imaging allows the
detection of myocardial edema,
allowing for early diagnosis of myo-cardial
ischemia, area at risk, and
salvage [22] (Fig. 4).
In chronic infarctions, the LGE is
a result of retention of contrast
medium in large interstitial space
between collagen fibres in the
fibrotic tissue.
Stunning and hibernating
myocardium
Cine imaging in combination with
delayed enhancement MRI allows
identification of:
1) Myocardial stunning: Stunning is
defined as post-ischemic myocardial
dysfunction (seen in the setting of
acute myocardial ischemia) which
persists despite restoration of normal
blood flow. Over time there can be
a gradual return of contractile func-tion
depending on transmurality of
the ischemia. If the degree of trans-murality
as seen on delayed
enhancement images is < 50%, the
myocardial function is likely to
recover.
2) Hibernating myocardium: A state
in which some segments of the
myocardium exhibit abnormalities
of contractile function at rest. This
phenomenon is clinically significant
since it manifests in the setting of
chronic ischemia that is potentially
reversible by revascularisation. The
reduced coronary perfusion causes
the myocytes to enter into a low
energy ‘sleep mode’ to conserve
energy. There is an inverse relation-ship
between transmural extent of
hyperenhancement, and likelihood
of wall motion recovery following
revascularisation [5].
Multiple experimental studies have
demonstrated excellent spatial correla-tion
between the extent of hyper-enhancement
and areas of myocardial
necrosis (acute MI) or scarring (chronic
MI) at histopathology.
Specifically, there is an inverse rela-tionship
between transmural extent of
hyperenhancement and likelihood of
wall motion recovery following revas-cularisation.
Hence it follows that
myocardial regions which show little
or no evidence of hyper-enhancement
(i.e. infarction) have a high likelihood
of recovery, whereas regions with
transmural hyperenhancement have
virtually no chance of recovery [9].
Moving from a 1.5T to a 3T system
involves doubling of SNR which can be
used to increase either spatial or tem-poral
resolution. This translates into
potentially increased contrast between
perfused and non-perfused images
leading to increased contrast-to-noise
ratio (CNR) with better LGE in setting
of chronic ischemia [1].
Figures 1–3 demonstrate LGE in the
RCA & LCX, LCX and LAD territories,
respectively, significant other non-via-ble
myocardium in these regions.
Table 3
Transmural
extent
LAD LCX RCA
> 50% 30 4 10
< 50% 5 2 4
Table 4
Indications
Number of
patients
1) Myocardial viability 55
2) Recent MI 2
3) Cardiomyopathies 15
a) Hypertrophic
cardiomyopathy
8
b) Dilated
cardiomyopathy
5
c) Non compaction
cardiomyopathy
2
d) Restrictive
cardiomyopathy
1
4) Cardiac masses 5
5) Congenital
heart disease
1
6) Pericardium
(constrictive
pericarditis)
2
Table 5 [9]: Differentiation between acute and chronic MI.
Acute MI Chronic MI
Bright on pre-contrast STIR (or T2w) imaging Not bright on pre-contrast STIR(or T2w) imaging
Walls may be thicker than usual Walls may be thinned
May have a ‘no-reflow zone’ Does not have a ‘no-reflow zone’
Myocardium
protected by
collateralisation
Myocardium
capable of
reperfusion
No reflow territory /
microvascular
obstruction
PSIR short axis image
acquired immediately
post Gd administration
in a 60-year-old female
patient reveals suben-docardial
1st pass defect
in the lateral wall (solid
white arrow).
PSIR images taken 15
minutes after Gd admin-istration
reveal subendo-cardial
LGE with trans-mural
extent suggestive
of non-viable
myocardium in the LCX
territory (solid white
arrow).
2A 2B
Cardiology Clinical
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Clinical Cardiology
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Abstract
Diagnostic clinical cardiac magnetic
resonance imaging (MRI) requires an
appropriate combination of temporal
and spatial resolution. Cardiovascular
imaging is making considerable
advances toward the fulfillment of
these requirements, largely because
of continued improvements in MRI
hardware and software. Optimal diag-nostic-
quality MRI implies a balance
among signal-to-noise ratio (SNR),
tissue contrast, acquisition time, and
spatial and temporal resolution. Mag-netic
field strength is one of the major
factors affecting image SNR [3]. The
transition from 1.5T to 3T has resulted
in faster imaging and better SNR.
However, cardiac MRI protocols on 3T
have not yet been optimized in the
way that they have been optimized
for 1.5T over the last decade.
This article illustrates 80 cases of car-diac
MRI imaged on a 3T MRI system
(MAGNETOM Verio, 32-channel sys-tem)
at our institution done between
January 2012 and August 2013. This
is probably the largest study of car-diac
MRI done on a 3T in India.
Introduction
The role of magnetic resonance
imaging (MRI) has significantly
evolved over the last decade. MRI is
now considered useful in the evalua-tion
of pericardium, complex congen-ital
heart disease, cardiac masses,
and ischemic heart disease for myo-cardial
viability, hibernating and
stunned myocardium and the right
ventricle.
In 2002, the US Food and Drug
Administration’s (FDA) approval of
3 Tesla opened the way for multiple
clinical applications. Compared to
1.5T, the higher field strength results
in doubling of SNR due to increased
spin polarisation. Furthermore, imag-ing
at higher field strengths with gad-olinium-
based agents can produce fur-ther
improvements in image contrast.
Cardiac imaging at 3T is, however,
noticeably different from imaging at
1.5T because of a variety of artifacts
that result from susceptibility effects
and augmentation of radiofrequency
(RF) inhomogeneity [3].
The adoption of 3T for body applica-tions,
especially cardiac applications,
has been somewhat slower. The
slower acceptance of 3T for cardiac
applications is due to the unique chal-lenges
posed by cardiac imaging:
Requirement of a large field-of-view,
the motion of the heart, position of
the heart within the body, proximity of
heart to the lungs, and high RF power
deposition required in many fast car-diac
imaging sequences [1]. Cardiac
MRI has largely been done on a 1.5T in
India. Due to optimization done on
1.5T and apprehension of challenges
on a 3T system, no significant work
was done on 3T in India. We present
probably the largest number of cardiac
MRI cases performed till date on a 3T
in India.
There are several advantages which
motivate users to perform cardiovascu-lar
magnetic resonance (CMR) at
higher filed strengths. First, the bulk
magnetisation increases as the mag-netic
field strength is increased result-ing
in higher SNR. Second, the increas-ing
field strength increases the
frequency separation of off-resonance
spins. The enhanced frequency differ-ences
may be exploited for improve-ment
in spectroscopic imaging and
potentially in fat suppression. A third
advantage is increased T1 signal of
many tissues, resulting in beneficial
effects in some applications, such as
myocardial tagging and myocardial
perfusion sequences [1].
Methods and Materials
A) Patient population
Eighty patients with an age range
of 5 to 70 years with a suspected
cardiac pathology were evaluated
by cardiac MRI (CMR) at our institute
from January 2012 to August 2013.
All patients had undergone a prior
echocardiography.
B) Patient preparation
A detailed history was elicited from
each patient including principal
symptoms and signs, echocardio-graphic
and cardiac catheterisation
data. For all patients in this study,
MR compatible electrocardiographic
leads were placed in the anterior
chest wall before imaging and
attached to the MR imaging unit
for electrocardiographic gating. For
most sequences, electrocardio-graphic
triggering was used to syn-chronise
imaging with the onset
of systole and offset cardiac motion
and match each image to the
desired cardiac phase.
C) Cardiac MRI protocol
Cardiac MRI was performed
using a whole-body 3T scanner
(MAGNETOM Verio, Siemens
Healthcare, Erlangen, Germany).
MR imaging protocol commenced
with a localiser using TrueFISP
(steady-state free precision)
sequence. A list of protocols is
given in table 2. Axial and coronal
scans of 5 mm slice thickness were
obtained from the aortic arch to
diaphragm. All diagnostic
sequences were acquired in stan-dard
angulations (4-, 2-chamber
view and short axis) using a matrix
of at least 256 × 256. Myocardial
function was evaluated by cine
TrueFISP sequences; T2-weighted
dark blood turbo spin echo
sequences were acquired 5 and
15 minutes after injection of
0.15 mmol gadolinium diethylene
triamine penta-acetic acid (DTPA)
(Magnevist, Schering, Berlin,
Germany) per kilogram of body
weight.
Inversion recovery prepared turbo
sequences (FLASH and TrueFISP) were
performed to visualise the myocardial
and blood pool gadolinium kinetics,
and to adjust inversion time. An
inversion time (TI) scout was acquired
and the optimal TI value was found.
Endocardial counters of the left ven-tricle
were manually drawn using
dedicated software (Argus, Siemens
Healthcare, Erlangen, Germany) to
calculate end-diastolic volume, end-systolic
volume, stroke volume and
ejection fraction of the left ventricle
[8]. In the case of evaluation of con-genital
heart diseases, scans were
obtained till below the diaphragm
including IVC and the hepatic veins
[23].
A summary of the basic cardiac
protocols is presented in table 1.
Modified sequences were acquired
for specific indications which have
been summarised in table 2.
D) Results
The study comprised 80 patients.
The age range was 5 to 70 years.
There were 57 male and 23 female
patients. The commonest indica-tion
for a CMR study was evalua-tion
of myocardial viability.
The variety of indications for
which cardiac MRI was performed
is summarised in table 4.
Images were analysed by one radi-ologist
and one cardiologist. The
morphological information com-prised
of chamber anatomy, thick-ness
of the ventricular walls and
assessment of presence and extent
of late gadolinium hyper-enhance-ment
on delayed post contrast
PSIR images.
Functional information comprised
of assessment of wall motion
abnormalities, calculation of ejec-tion
fraction and evaluation of
the outflow tracts.
In cases of congenital heart dis-ease,
cine imaging in horizontal
long axis provided dynamic infor-mation
of the cardiac size, valve
morphology, wall thickness cham-ber
size, and septum morphology
and aortopulmonary connections
[23].
55 patients were referred for eval-uation
of myocardial viability. Of
these, 30 showed transmural late
gadolinium enhancement (LGE) in
68-year-old male patient
imaged for evaluation of
myocardial viability. PSIR
sequence taken 15 minutes
post Gd administration
reveals transmural LGE in
the inferior wall conforming
to RCA and the LCX territory
(solid white arrows)
suggestive of non-viable
myocardium.
Horizontal long axis view
of the same patient
showing the extent of
transmural LGE.
1A 1B
Cardiology Clinical
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Clinical Cardiology
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![Myocardial Tissue Imaging Using
Simultaneous Cardiac Molecular MRI
James A. White, M.D., FRCPC
The Lawson Health Research Institute, London, Ontario, Canada
Molecular MRI in London
Ontario
The Lawson Health Research Institute
(the “Lawson”) is located within
St. Joseph’s Healthcare in London
Ontario, and is affiliated with West-ern
University. This group received
the first Biograph mMR in Canada
in March 2012. With strong existing
research groups in MRI and nuclear
medicine this group is ideally posi-tioned
to drive research and innova-tion
using this platform. In advance
of the installation of the hybrid
molecular MR, researchers at the
Lawson had been developing novel
MR-based attenuation correction
methods, and novel tracer develop-ments.
In addition to the molecular
MR this site has a PET-CT, a SPECT-CT,
and an Inveon small animal PET as
well as two 1.5T MAGNETOM Aera
systems, a 16.5MeV medical cyclo-tron
and radiochemistry facilities.
Myocardial tissue imaging
Hybrid imaging platforms incorporat-ing
PET have become available for
cardiovascular imaging applications
over the past decade. These platforms
have been primarily aimed at provid-ing
superior tissue attenuation correc-tion
of the emitted photon signal and
to provide spatial anatomic registra-tion
for the localization of abnormal
tracer signal. While this has resulted in
substantial improvements in the clini-cal
performance of cardiac PET, the
exploitation of complementary imag-ing
data has yet to be fully realized.
The recent availability of hybrid plat-forms
allows for an expansive range
of PET applications to be explored.
For example the capacity of cardiovas-cular
MRI to provide complementary
2D and 3D morphological data with
excellent soft tissue contrast and high
temporal resolution is of benefit for
anatomic registration and novel motion
correction algorithms. However, its
incremental capacity to provide exqui-site
tissue characterization through
intrinsic tissue contrast and altered
kinetics of exogenous paramagnetic
contrast is of particular interest in the
context of the PET imaging
environment.
Clinical adoption of myocardial tissue
imaging is expanding in response to
mounting evidence that the ‘health’ of
myocardium strongly modulates bene-fit
from heart failure therapies (phar-macologic,
surgical and device-based)
and is predictive of future arrhythmic
events among patients with ischemic
and non-ischemic cardiomyopathy
[1-5]. To date, this literature has
focused on isolated and disparate
markers of tissue health using both PET
and MRI. However, within this brief
report we discuss several synergies of
these platforms that hold promise
towards a new era of hybrid imaging
for the optimal performance of
myocardial tissue imaging.
Molecular MRI in the setting
of acute ischemic injury
Among those surviving acute myocar-dial
infarction (AMI), appropriate myo-cardial
healing is believed to be reliant
upon a highly choreographed process
of early inflammatory cell invasion,
collagen degredation, debris removal
by activated macrophages, and myofibroblast
proliferation with reconstitu-tion
of a new collagen matrix. While
1
1 The Lawson Health Research Institute.
2A 2B 2C
Example of a non-reperfused myocardial infarction from LAD ligation in a canine model, imaged one week post ligation. A large
area of microvascular obstruction (MO) is seen by LGE imaging with a corresponding marked prolongation of T1 shown using
MOLLI-based T1 mapping. Simultaneously acquired FDG imaging (binned to cardiac phase) has been fused to both LGE imaging
and raw T1 map and illustrates a marked reduction in inflammation within the region of MO. There is intense inflammatory
activity evident within the perfused infarct rim.
such findings can be characterized
histologically, our capacity to quantify
markers of the inflammatory process
in vivo, and evaluate influences of its
modulation on the remodeling process
has been limited.
We have started examining this pro-cess
in a canine infarct model using
the Biograph mMR 3T-PET platform
using simultaneous 3D LGE / 18F-FDG
imaging, the latter imaged following
normal myocardial glucose metabolism
using intravenous heparin and lipid
infusion. In these experiments we have
focused on evaluating the influence
of microvascular obstruction (MO) on
mitigating appropriate inflammatory
cell recruitment to the infarct core –
a postulated mechanism of how MO
may adversely impact on left ventricu-lar
remodeling post infarct. Figure
2
illustrates how the region of MO can
be elegantly visualized using both
LGE imaging and T1 mapping CMR
techniques. 18F-FDG imaging shows
intense inflammatory activity within
the perfused infarct rim, however a
marked reduction in activity is seen
in regions of MO. This imaging may
therefore provide novel insights
towards mechanisms by which MO
contributes to adverse outcomes fol-lowing
AMI, and offers a new tool
to evaluate therapies aimed at modu-lation
of this pathway.
Molecular MRI in the setting
of acute non-ischemic
(inflammatory) injury
Both PET and CMR have been investi-gated
for their diagnostic accuracy
in the setting of suspected inflamma-tory
cardiomyopathy – particularly
among patients with known pulmo-nary
Sarcoid. While their respective
diagnostic performance has been
compared in the past, this remains
inappropriate, as the information
gathered and interpreted from each
technique could not be more unique.
PET imaging (typically performed
using 18F-FDG following prolonged
fasting, fatty meal consumption and
intravenous heparin to suppress nor-mal
myocardial glucose utilization)
exploits the hypermetabolic signal
of activated inflammatory cells (i.e.
macrophages) and therefore indi-cates
disease ‘activity’ among patients
with active cardiac Sarcoid. In con-trast,
LGE imaging indicates regions
of mature granulomatous fibrosis
among patients with prior or current
cardiac Sarcoid. Therefore, these two
commonly employed diagnostic tech-niques
provide complementary but
unique information.
2
LGE T1-map (raw) T1-map (color)
LGE / FDG FDG (raw) T1-map/FDG
2D 2E 2F
Cardiology Clinical
MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world 37
Clinical Cardiology
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![Clinical Cardiology Cardiology Clinical
Figure 3 illustrates the capacity of
hybrid MR and PET to spatially register
these techniques using simultane-ously
acquired data, and potentially
improve diagnostic accuracy while
expanding our understanding of dis-ease
pathophysiology. In this case
of a 72-year-old female presenting
with heart failure and non-sustained
ventricular tachycardia we can iden-tify
a leading edge of inflammation
(intense FDG uptake) with a trailing
edge of irreversible injury or ‘scar’
(indicated by hyperenhancement
on LGE imaging) at the sub-epicardial
zone. This approach ushers in a new
era of imaging for inflammatory-mediated
disease where a more com-plete
spectrum of disease activity
can be visualized in a single, spatially
registered examination.
Molecular MRI in the setting
of non-acute myocardial
disease
Another clinical setting where MR
and PET have established their respec-tive
roles for therapeutic decision-making
is for the assessment of
tissue viability in chronic ischemic
cardiomyopathy. Evidence supports
that both the regional reduction of
FDG signal [6, 7] and regional scar
transmurality by LGE are strongly
predictive of absence of functional
recovery following coronary revas-cularization.
The performance
of these studies are therefore
commonly considered to be mutually
exclusive, with absence of FDG signal
being the sine qua non of myocardial
scar, and the lack of scar by LGE
imaging being equivalent to tissue
health. However, it is recognized that
the spatial resolution and signal-to-noise
of LGE imaging is superior to
FDG for the detection of subendocar-dial
scar, and also for the character-ization
of tissue viability among
those with marked thinning of the
ventricular wall [8]. Conversely, FDG-PET
based metabolic abnormalities
can be documented within tissue
that fails to demonstrate myocardial
scar on LGE MRI, lack of FDG uptake
being predictive of absence of func-tional
recovery. Accordingly, the
marriage of PET-based metabolic imag-ing
and LGE-based scar imaging may
provide a more robust platform for the
prediction of improved outcomes
following coronary revascularization.
In figure 4 we see a 42-year-old male
referred for viability imaging prior to
coronary artery bypass surgery late
following
myocardial infarction. Cine
imaging shows a large region of
thinned and akinetic myocardium in
the distribution of the left anterior
descending artery, this territory dem-onstrating
varying degrees of trans-mural
scar following gadolinium
administration. Simultaneous MR and
PET with 18F FDG imaging shows meta-bolic
activity within non-scarred
regions surrounding the infarct zone
and normal metabolic tracer activity
within remote myocardium.
4
42-year-old male
with large anterior
wall myocardial
infarction being
considered for
surgical revascular-ization
in the
setting of triple
vessel disease. Cine
MRI shows akinesia
of the septum and
apex with a
reduced ejection
fraction of 32%.
Late gadolinium
enhancement (LGE)
imaging shows a
large infarct of the
LAD territory with
variable scar trans-murality
ranging
from 25% to 100%
throughout the
infarct region.
FDG-PET imaging,
shown fused with
LGE imaging, shows
matched reductions
in metabolic tracer
uptake.
72-year-old female with suspected new-onset heart failure and non-sustained ventricular tachycardia and prior history of
biopsy-
proven systemic Sarcoid. Top rows show late gadolinium enhancement (LGE) imaging with characteristic sub-epicaridal
based scar (arrows), consistent with prior inflammatory injury. Lower row shows fused FDG-PET images with evidence
of focal signal enhancement, consistent with active inflammation surrounding regions of established scar.
3
References
1 Gulati A, Jabbour A, Ismail TF, Guha K,
Khwaja J, Raza S, Morarji K, Brown TD,
Ismail NA, Dweck MR, Di Pietro E, Roughton M,
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Alpendurada F, Lyon AR, Cook SA, Cowie MR,
Assomull RG, Pennell DJ, Prasad SK.
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sudden cardiac death in patients with
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2 Gao P, Yee R, Gula L, Krahn AD, Skanes A,
Leong-Sit P, Klein GJ, Stirrat J, Fine N,
Pallaveshi L, Wisenberg G, Thompson TR,
Prato F, Drangova M, White JA. Prediction of
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3 Kwon DH, Halley CM, Carrigan TP, Zysek V,
Popovic ZB, Setser R, Schoenhagen P,
Starling RC, Flamm SD, Desai MY. Extent of
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Imaging 2013;6;363-372.
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Contact
James A. White, M.D., FRCPC
Robarts Research Institute
P.O. Box 5015, 100 Perth Drive
London ON, Canada
N5K 5K8
Phone: +1 519-663-5777
jawhit@ucalgary.ca
4 Klem I, Shah DJ, White RD, Pennell DJ,
van Rossum AC, Regenfus M, Sechtem U,
Schvartzman PR, Hunold P, Croisille P,
Parker M, Judd RM, Kim RJ. Prognostic value
of routine cardiac magnetic resonance
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fraction and myocardial damage: An inter-national,
multicenter study. Circ Cardiovasc
Imaging. 2011;4:610-619.
5 Neilan TG, Coelho-Filho OR, Danik SB,
Shah RV, Dodson JA, Verdini DJ, Tokuda M,
Daly CA, Tedrow UB, Stevenson WG,
Jerosch-Herold M, Ghoshhajra BB, Kwong
RY. CMR quantification of myocardial scar
provides additive prognostic information
in nonischemic cardiomyopathy. JACC
Cardiovasc Imaging. 2013;6:944-954.
6 Romero, J, Xue X, Gonzalez W, Garcia MJ.
CMR Imaging Assessing Viability in Patients
3A 3B 3C
3D 3E 3F
4A 4B
4C 4D
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SCMR Edition – Issue 56
- 1. MAGNETOM Flash The Magazine of MRI Issue Number 1/2014 | SCMR Edition 56 Editorial Comment Orlando Simonetti Page 2 The Clinical Role of T1 and T2 Mapping Page 6 Myocardial T1 Mapping Techniques and Clinical Application Page 10 Compressed Sensing for the Assessment of Left Ventricular Function Page 18 Accelerated Segmented Cine TrueFISP Using k-t-sparse SENSE Page 27 mMR in Hypertrophic Cardiomyopathy Page 32 mMR for Myocardial Tissue Imaging Page 36 Not for distribution in the US
- 2. Editorial Orlando P. Simonetti, Ph.D., is a Professor of Internal Medicine and Radiology at The Ohio State University in Columbus, Ohio. He joined the OSU faculty in 2005 as the Research Director of Cardiovascular MR and CT. His current research interests include fast imaging, flow quantification, parameter mapping, and exercise stress CMR. Dr. Simonetti has dedicated his entire career to the advance-ment of cardiovascular magnetic resonance technology, and is widely recognized for his contributions to the field. Dear MAGNETOM Flash reader, One could easily argue that cardio-vascular magnetic resonance (CMR) is in the midst of another technical revolution. Those of us who have worked in the field for the last two decades have seen similar periods in the past, when major advances in hardware technology like array coils and fast gradients, in software technology like parallel acquisition techniques, and pulse sequences like balanced steady-state free precession have spawned dramatic improvements in the efficiency and effectiveness of CMR. Three of the most exciting recent advances: myocardial parameter mapping, MR-PET, and compressed sensing are highlighted in the six articles of this issue of MAGNETOM Flash. Relaxation parameter mapping has initiated an exciting new direc-tion of research into the clinical implications of diffuse changes in myocardial tissue (e.g., fibrosis or edema) that can accompany a variety of diseases. The novel combination of CMR and PET is enabling the power-ful diagnostic combination of the exquisite assessment of myocardial tissue structure and function pro-vided by CMR, together with the eval-uation of metabolism by PET. New approaches to sampling and recon-struction using compressed sensing are dramatically reducing the data acquisition requirements, and thereby significantly enhancing the efficiency of CMR. Together, these advances are indicative of the ever-changing nature of CMR; a technology that continues to improve thanks to the passion, creativity, and tireless effort of the researchers around the world who have made this their life’s work. The article by Moon et al., from University College London Hospitals, London, UK, discusses recent trends in the development and investigation of techniques for quantitative mapping of myocardial T1 and T2 relaxation parameters. Quantitative mapping addresses many of the technical limi-tations of conventional T1-weighted and T2-weighted sequences, most importantly offering the capability to assess diffuse changes in myocardial tissue that can accompany many dis-ease states. The article by Fernandes et al., from University of Campinas, Brazil, nicely summarizes the tech-niques that are employed for myocar-dial T1 mapping, and reviews recent investigations of this technology in patients with a variety of diseases including amyloid, aortic stenosis, and various cardiomyopathies. As noted in both articles, the early evidence suggests that myocardial relaxation parameter mapping has fantastic poten-tial as a diagnostic tool that may be sensitive to early pathological changes in myocardial tissue potentially missed by other imaging methods. Challenges remain in standardization of these methods to ensure consistent quantitative results across patients and imaging platforms. The article by Schwitter et al., from the Cardiac Magnetic Resonance Center of the University Hospital of Lausanne in Switzerland nicely demonstrates an important advantage of highly acceler-ated cine imaging using compressed sensing data acquisition and recon-struction strategies. The ability to acquire sufficient cine slices to cover the entire heart in multiple orienta-tions in a single breath-hold (2 beats per slice) not only reduces exam times, but also facilitates more accurate LV volume calculations using a three dimensional modeling approach rather than the traditional Simpson’s Method. Reducing the potential for mis-regis-tration of slices avoids one of the pri-mary limitations of the 3D approach to LV volume calculations. Thus, the effi-ciency gains achieved via compressed sensing data acquisition and recon- Editorial “The 3 new technologies of myocardial parameter mapping, CMR-PET, and compressed sensing offer the potential to significantly improve the efficiency and effectiveness of CMR, and to expand the information CMR can provide to physicians to better diagnose and treat cardiovascular disease.” Orlando P. Simonetti, Ph.D. struction strategies can positively impact the clinical value of CMR from several different perspectives. The article by Carr et al., from the group at Northwestern University in Chicago highlights the tremendous potential of iterative reconstruction techniques to dramatically accelerate cardiac cine imaging. The results shown indicate that efficiency gains of at least a factor of two are possible over con-ventional parallel acquisition tech-niques. The time-consuming nature of most CMR techniques, and the require-ments of repeated patient breath-holds and regular cardiac rhythm are factors that have constrained the widespread acceptance of CMR into the clinical routine. While there is still work remaining to optimize data sampling and reduce image reconstruction times, the gains in scanning efficiency demonstrated in this study could have far-reaching implications in moving CMR further into the mainstream as a cost-effective diagnostic imaging modality. The potential advantages of simulta-neous CMR and PET acquisitions are explored in two articles of this issue of MAGNETOM Flash. Drs. Cho and Kong from Yeungnam University Hospital, Daegu, South Korea, demonstrate in a patient with hypertrophic cardiomyo-pathy the ability to characterize myo-cardial fibrosis using both Late Gado-linium Enhancement and 18F-FDG PET. The article by Dr. James A. White from The Lawson Health Research Institute, London, Ontario, Canada, nicely describes the potential for advanced myocardial tissue charac-terization using the synergistic capa-bilities of CMR and PET. Dr. White points out how the complementary and unique information provided by CMR and PET may better characterize pathological changes in myocardial tissue in diseases such as sarcoidosis. The evaluation of cellular metabolic activity using PET may fill the role that MR spectroscopy has promised but as yet been unable to deliver in the clinical setting. The field of meta-bolic imaging is rapidly evolving, however, and the continued develop-ment of hyperpolarized 13C offers exciting possibilities as well. In summary, the three new technolo-gies of myocardial parameter mapping, CMR-PET, and compressed sensing discussed in this issue represent some of the most exciting recent advances in CMR. They offer the potential to significantly improve the efficiency and effectiveness of CMR, and to expand the information CMR can pro-vide to physicians to better diagnose and treat cardiovascular disease. Review Board Lars Drüppel, Ph.D. Global Segment Manager Cardiovascular MR Sunil Kumar S.L., Ph.D. Senior Manager Applications Reto Merges Head of Outbound Marketing MR Applications Edgar Müller Head of Cardiovascular Applications Heike Weh Clinical Data Manager Michael Zenge, Ph.D. Cardiovascular Applications Editorial Board Antje Hellwich Associate Editor Wellesley Were MR Business Development Manager Ralph Strecker MR Collaborations Manager Sven Zühlsdorff, Ph.D. Clinical Collaboration Manager Gary R. McNeal, MS (BME) Adv. Application Specialist Peter Kreisler, Ph.D. Collaborations & Applications We appreciate your comments. Please contact us at magnetomworld.med@siemens.com 2 MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world 3
- 3. Add a new layer of pixel-based diagnostic information to cardiac diagnoses. Based on HeartFreeze Inline Motion Correction, MyoMaps1 provides pixel-based myocardial quantification, on the fly. Now address diffuse, myocardial pathologies (T1 Map), cardiac edema (T2 Map) and improve early detection of iron overload (T2* Map) to guide cardiovascular therapy, starting earlier and more efficiently. T1 Map courtesy of Peter Kellman, National Institutes of Health, Bethesda, USA. Content 6 New generation cardiac parametric mapping: The clinical role of T1 and T2 mapping James C. Moon, et al. 10 Myocardial T1 mapping: Techniques and clinical applications Juliano Lara Fernandes, et al. 18 Preliminary experiences with compressed sensing1 multi-slice cine acquisitions for the assessment of left ventricular function J. Schwitter, et al. 27 Accelerated segmented cine TrueFISP of the heart on a 1.5T MAGNETOM Aera using k-t-sparse SENSE1 Maria Carr, et al. Content 32 Combined 18F-FDG PET and MRI evaluation of a case of hypertrophic cardiomyopathy using Biograph mMR Ihn-ho Cho, et al. 36 Myocardial tissue imaging using simultaneous cardiac molecular MRI James A. White Imprint 4 MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world The information presented in MAGNETOM Flash is for illustration only and is not intended to be relied upon by the reader for instruction as to the practice of medicine. Any health care practitioner reading this information is reminded that they must use their own learning, training and expertise in dealing with their individual patients. This material does not substitute for that duty and is not intended by Siemens Medical Solutions to be used for any purpose in that regard. The treating physician bears the sole responsibility for the diagnosis and treatment of patients, including drugs and doses prescribed in connection with such use. The Operating Instructions must always be strictly followed when operating the MR System. The source for the technical data is the corresponding data sheets. The statements by Siemens’ customers described herein are based on results that were achieved in the customer’s unique setting. Since there is no “typical” setting and many variables exist there can be no guarantee that other customers will achieve the same results. 1 WIP, the product is currently under development and is not for sale in the US and other countries. Its future availability cannot be ensured. Not for distribution in the US. MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world 5 The entire editorial staff at The Ohio State University and at Siemens Healthcare extends their appreciation to all the radiologists, technologists, physicists, experts and scholars who donate their time and energy – without payment – in order to share their expertise with the readers of MAGNETOM Flash. MAGNETOM Flash – Imprint © 2014 by Siemens AG, Berlin and Munich, All Rights Reserved Publisher: Siemens AG Medical Solutions Business Unit Magnetic Resonance, Karl-Schall-Straße 6, D-91052 Erlangen, Germany Guest Editor: Orlando P. Simonetti, Ph.D. Professor of Internal Medicine and Radiology The Ohio State University, Columbus, Ohio, USA Associate Editor: Antje Hellwich (antje.hellwich@siemens.com) Editorial Board: Wellesley Were; Ralph Strecker; Sven Zühlsdorff, Ph.D.; Gary R. McNeal, MS (BME); Peter Kreisler, Ph.D. Production: Norbert Moser, Siemens AG, Medical Solutions Layout: independent Medien-Design Widenmayerstrasse 16, D-80538 Munich, Germany Printer: infowerk GmbH Wiesentalstraße 40, D-90419 Nürnberg, Germany Note in accordance with § 33 Para.1 of the German Federal Data Protection Law: Despatch is made using an address file which is maintained with the aid of an automated data processing system. MAGNETOM Flash is sent free of charge to Siemens MR customers, qualified physicians, technologists, physicists and radiology departments throughout the world. It includes reports in the English language on magnetic resonance: diagnostic and therapeutic methods and their application as well as results and experience gained with corresponding systems and solutions. It introduces from case to case new principles and proce-dures and discusses their clinical poten-tial. The statements and views of the authors in the individual contributions do not necessarily reflect the opinion of the publisher. The information presented in these articles and case reports is for illustration only and is not intended to be relied upon by the reader for instruction as to the practice of medicine. Any health care practitioner reading this information is reminded that they must use their own learning, training and expertise in dealing with their individual patients. This material does not substitute for that duty and is not intended by Siemens Medical Solutions to be used for any purpose in that regard. The drugs and doses mentioned herein are consistent with the approval labeling for uses and/or indications of the drug. The treating physician bears the sole responsibility for the diagnosis and treatment of patients, including drugs and doses prescribed in connection with such use. The Operating Instructions must always be strictly followed when operating the MR system. The sources for the technical data are the corresponding data sheets. Results may vary. Partial reproduction in printed form of individual contributions is permitted, provided the customary bibliographical data such as author’s name and title of the contribution as well as year, issue number and pages of MAGNETOM Flash are named, but the editors request that two copies be sent to them. The written consent of the authors and publisher is required for the complete reprinting of an article. We welcome your questions and comments about the editorial content of MAGNETOM Flash. Please contact us at magnetomworld.med@siemens.com. Manuscripts as well as suggestions, proposals and information are always welcome; they are carefully examined and submitted to the editorial board for attention. MAGNETOM Flash is not responsible for loss, damage, or any other injury to unsolicited manuscripts or other materials. We reserve the right to edit for clarity, accuracy, and space. Include your name, address, and phone number and send to the editors, address above. MAGNETOM Flash is also available on the internet: www.siemens.com/magnetom-world
- 4. Clinical Cardiology Cardiology Clinical New Generation Cardiac Parametric Mapping: the Clinical Role of T1 and T2 Mapping T1 mapping Initial T1 measurement methods were multi-breath-hold. These were time consuming and clunky, but were able to measure well diffuse myocardial fibrosis, a fundamental myocardial property with high potential clinical significance [1]. Healthy volunteers and those with disease had different extents of diffuse fibrosis [2], and these were shown to be clinically significant in a number of diseases. T1 mapping methods based on the MOLLI* approach with modifications for shorter breath-holds, better heart rate independence and better image registration for cleaner maps, however, transformed the field – albeit still with a variety of potential sequences in use [3-5]. There are two key ways of using T1 mapping: Without (or Viviana Maestrini; Amna Abdel-Gadir; Anna S. Herrey; James C. Moon The Heart Hospital Imaging Centre, University College London Hospitals, London, UK designed to optimize contrast between ‘normal’ and abnormal – a dichotomy of health and disease. As a result, global myocardial patholo-gies such as diffuse infiltration (fibro-sis, amyloid, iron, fat, pan-inflamma-tion) are missed. Recently, rapid technical innovations have generated new ‘mapping’ tech-niques. Rather than being ‘weighted’, these create a pixel map where each pixel value is the T1 or T2 (or T2*), displayed in color. These new sequences are single breath-hold, increasingly robust and now widely available. With T1 mapping, clever contrast agent use also permits the measurement of the extracellular volume (ECV), quantifying the inter-stitium (odema, fibrosis or amyloid), also as a map. Early results with these methodologies are exciting – poten-tially representing a new era of CMR. Introduction Cardiovascular magnetic resonance (CMR) is an essential tool in cardiol-ogy and excellent for cardiac function and perfusion. However, a key, unique advantage is its ability to directly scrutinize the fundamental material properties of myocardium – ‘myocar-dial tissue characterization’. Between 2001 and 2011, the key methods for tissue characterization have been sequences ‘weighted’ to a magnetic property – T1-weighted imaging for scar (LGE) and T2-weighted for edema (area at risk, myocarditis). These, particularly LGE imaging, have changed our understanding and clini-cal practice in cardiology. However, there are limitations to these approaches: Both are difficult to quantify – the LGE technique in particular is very robust in infarction, but harder to quantify in non-ischemic cardiomyopathy. A more fundamental difference is that sequences are before) contrast – Native T1 mapping; and with contrast, typically by sub-tracting the pre and post maps with hematocrit correction to generate the ECV [6]. Native T1 Native T1 mapping (pre-contrast T1) can demonstrate intrinsic myocardial contrast (Fig. 1). T1, measured in mil-liseconds, is higher where the extra-cellular compartment is increased. Fibrosis (focal, as in infarction, or dif-fuse) [7-8], odema [9-10] and amy-loid [11], are examples. T1 is lower in lipid (Anderson Fabry disease, AFD) [12], and iron [13] accumulation. These changes are large in some rare disease. Global myocardial changes are robustly detectable without con-trast, even in early disease. In iron, AFD and amyloid, changes appear before any other abnormality – there may be no left ventricular hypertrophy, a nor-mal electrocardiogram, and normal conventional CMR, for example – gen-uinely new information. In established disease, low T1 values in AFD appear to absolutely distinguish it from other causes of left ventricular hypertrophy [12] whilst in established amyloid T1 elevation tracks known markers of cardiac severity [11]. A note of caution, however. Native T1, although stable between healthy volunteers to 1 part in 30, is depen-dent on platform (magnet manufac-turer, sequence and sequence variant, field strength) [14]. Normal reference ranges for your setup are needed. Lowest ECV Tertile Middle ECV Tertile Highest ECV Tertile p < 0.001 fortrend p < 0.015 for Middle Tertile compared to others 2 ECV in non scar areas (LGE excluded) is associated with all-cause mortality [21]. The signal acquired is also a compos-ite signal – generated by both inter-stitium and myocytes. The use of an extracellular contrast agent adds another dimension to T1 mapping and the ability to characterize the extracellular compartment specifically. Extracellular volume (ECV) Initially, post-contrast T1 was mea-sured, but this is confounded by renal clearance, gadolinium dose, body composition, acquisition time post bolus, and hematocrit. Better is mea-suring the ECV. The ratio of change of T1 between blood and myocardium after contrast, at sufficient equilibrium (e.g. after 15 minutes post-bolus – no infusion generally needed) [15, 16], represents the contrast agent parti-tion coefficient [17], and if corrected for the hematocrit, the myocardial extracellular space – ECV [1]. The ECV is specific for extracellular expansion, and well validated. Clinically this occurs in fibrosis, amyloid and odema. To distinguish, the degree of ECV change and the clinical context is important. A multiparametric approach (e. g. T2 mapping or T2-weighted imaging in addition) may therefore be useful. Amyloid can have far higher ECVs than any other disease [18] whereas ageing has small changes – near the detection limits, but of high potential clinical impor-tance [19, 20]. For low ECV expan-sion diseases, biases from blood pool partial volume errors need to be metic-ulously addressed. Nevertheless, even modest ECV changes appear prognos-tic. In 793 consecutive patients (all-comers but excluding amyloid and HCM, measuring outside LGE areas) followed over 1 year, global ECV pre-dicted short term-mortality (Fig. 2) 2 3A 3B 3C 100% A patient with myocarditis. On the left side a native T1 map showing the higher T1 value in the inferolateral wall (1115 ms); in the centre, a post-contrast T1 map showing the shortened T1 value after contrast administration (594 ms); on the right side the derived ECV map showing higher value of ECV (58%) compared to remote myocardium. 3 0% Proportion Surviving Years of Follow-up 1.0 0.9 0.8 0.7 0.6 0.5 0 0.5 1.0 1.5 2.0 * The product is currently under develop-ment; is not for sale in the U.S. and other countries, and its future availability cannot be ensured. 1 Native T1 maps of (1A) healthy volunteer (author VM): the myocardium appears homogenously green and the blood is red; (1B) cardiac amyloid: the myocardium has a higher T1 (red); (1C) Anderson Fabry disease: the myocardium has a lower T1 (blue) from lipid – except the inferolateral wall where there is red from fibrosis; (1D) myocarditis, the myocardium has a higher T1 (red) from edema, which is regional; (1E) iron overload: the myocardium has a lower T1 (blue) from iron. 1A 1B 1C 1D 1E 6 MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world Reprinted from MAGNETOM Flash 5/2013 Reprinted from MAGNETOM Flash 5/2013 MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world 7
- 5. Clinical Cardiology Cardiology Clinical Progress is rapid; challenges remain. Delivery across sites and standard-ization is now beginning with new draft guidelines for T1 mapping in preparation. Watch this space. References 1 Flett AS, Hayward MP, Ashworth MT, Hansen MS, Taylor AM, Elliott PM, McGregor C, Moon JC. Equilibrium Contrast Cardiovascular Magnetic Resonance for the measurement of diffuse myocardial fibrosis: preliminary validation in humans. Circulation 2010;122:138-144. 2 Sado DM, Flett AS, Banypersad SM, White SK, Maestrini V, Quarta G, Lachmann RH, Murphy E, Mehta A, Hughes DA, McKenna WJ, Taylor AM, Hausenloy DJ, Hawkins PN, Elliott PM, Moon JC. Cardiovascular magnetic resonance measurement of myocardial extracellular volume in health and disease. Heart 2012;98:1436-1441. 3 Piechnik SK, Ferreira VM, Dall’Armellina E, Cochlin LE, Greiser A, Neubauer S, Robson MD. Shortened Modified Look- Locker Inversion recovery (ShMOLLI) for clinical myocardial T1 mapping at 1.5 and 3 T within a 9 heartbeat breathhold. J Cardiovasc Magn Reson 2010;12:69. 4 Messroghli DR, Greiser A, Fröhlich M, Dietz R, Schulz-Menger J. Optimization and validation of a fully-integrated pulse sequence for modified look-locker inversion-recovery (MOLLI) T1 mapping of the heart. J Magn Reson Imaging 2007;26:1081–1086. 5 Fontana M, White SK, Banypersad SM, Sado DM, Maestrini V, Flett AS, Piechnik SK, Neubauer S, Roberts N, Moon JC. Comparison of T1 mapping techniques for ECV quantification. Histological validation and reproducibility of ShMOLLI versus multibreath-hold T1 quantification equilibrium contrast CMR. J Cardiovasc Magn Reson 201;14:88. 6 Kellman P, Wilson JR, Xue H, Ugander M, Arai AE. Extracellular volume fraction mapping in the myocardium, part 1: evaluation of an automated method. J Cardiovasc Magn Reson 2012;14:63. 7 Dass S, Suttie JJ, Piechnik SK, Ferreira VM, Holloway CJ, Banerjee R, Mahmod M, Cochlin L, Karamitsos TD, Robson MD, Watkins H, Neubauer S. Myocardial tissue characterization using magnetic resonance non contrast T1 mapping in hypertrophic and dilated cardiomyopathy. Circ Cardiovasc Imaging. 2012; 6:726-33. 8 Puntmann VO, Voigt T, Chen Z, Mayr M, Karim R, Rhode K, Pastor A, Carr-White G, Razavi R, Schaeffter T, Nagel E. Native T1 mapping in differentiation of normal myocardium from diffuse disease in hypertrophic and dilated cardiomy-opathy. J Am Coll Cardiovasc Imgaging 2013;6:475–84. Contact Dr. James C. Moon The Heart Hospital Imaging Centre University College London Hospitals 16–18 Westmoreland Street London W1G 8PH UK Phone: +44 (20) 34563081 Fax: +44 (20) 34563086 james.moon@uclh.nhs.uk 4A 4B 4C 4D (4A) T2 mapping in a normal volunteer (author VM). (4B) High T2 value in patient with myocarditis – here epicardial edema. (4C) Edema in acute myocardial infarction – here patchy due to microvascular obstruction – see LGE, (4D). 4 [21]. The same group also found (n ~1000) higher ECVs in diabetics. Those on renin-angiotensin-aldoste-rone system blockade had lower ECVs. ECV also predicted mortality and/or incident hospitalization for heart failure in diabetics [22]. The use and capability of ECV quanti-fication is growing. T1 mapping is getting better and inline ECV maps are now possible where each pixel carries directly the ECV value (Fig. 3) – a more biologically relevant figure than T1 [6]. T2 mapping T2-weighted CMR identifies myocar-dial odema both in inflammatory pathologies and acute ischemia, delin-eating the area at risk. However, these imaging techniques (e. g. STIR) are fragile in the heart and can be chal-lenging, both to acquire and to inter-pret. Preliminary advances were made with T2-weighted SSFP sequences, which reduce false negatives and positives [23, 24]. T2 mapping seems a further increment [25] (Fig. 4). As with T1 mapping, global diseases such as pan-myocarditis may now be iden-tified by T2 mapping, and preliminary results are showing this in several rheumatologic diseases (lupus, sys-temic capillary leak syndrome) and transplant rejection, detecting early rejection missed by other modalities [26, 27]. Conclusion Mapping – T1, T2, ECV mapping of myocardium is an emerging topic with the potential to be a powerful tool in the identification and quantification of diffuse myocardial processes with-out biopsy. Early evidence suggests that this technique detects early stage disease missed by other imaging methods and has potential as a prog-nosticator, as a surrogate endpoint in trials, and to monitor therapy. 9 Ferreira VM, Piechnik SK, Dall’Armellina E, Karamitsos TD, Francis JM, Choudhury RP, Friedrich MG, Robson MD, Neubauer S. Non-contrast T1 mapping detects acute myocardial edema with high diagnostic accuracy: a comparison to T2-weighted cardiovascular magnetic resonance. J Cardiovasc Magn Reson 2012; 14:42. 10 Dall’Armellina E, Piechnik SK, Ferreira VM, Si Ql, Robson MD, Francis JM, Cuculi F, Kharbanda RK, Banning AP, Choudhury RP, Karamitsos TD, Neubauer S. Cardio-vascular magnetic resonance by non contrast T1 mapping allows assessment of severity of injury in acute myocardial infarction. J Cardiovasc Magn Reson 2012;14:15. 11 Karamitsos TD, Piechnik SK, Banypersad SM, Fontana M, MD, Ntusi NB, Ferreira VM, Whelan CJ, Myerson SG, Robson MD, Hawkins PN, Neubauer S, Moon JC. Non-contrast T1 Mapping for the Diagnosis of Cardiac Amyloidosis. J Am Coll Cardiol Img 2013;6:488–97. 12 Sado DM, White SK, Piechnik SK, Banypersad SM, Treibel T, Captur G, Fontana M, Maestrini V, Flett AS, Robson MD, Lachmann RH, Murphy E, Mehta A, Hughes D, Neubauer S, Elliott PM, Moon JC. Identification and assessment of Anderson-Fabry Disease by Cardiovas-cular Magnetic Resonance Non-contrast myocardial T1 Mapping clinical perspective. Circ Cardiovasc Imaging 2013;6:392-398. 13 Pedersen SF, Thrys SA, Robich MP, Paaske WP, Ringgaard S, Bøtker HE, Hansen ESS, Kim WY. Assessment of intramyocardial hemorrhage by T1-weighted cardiovas-cular magnetic resonance in reperfused acute myocardial infarction. J Cardiovasc Magn Reson 2012; 14:59. 14 Raman FS, Kawel-Boehm N, Gai N, Freed M, Han J, Liu CY, Lima JAC, Bluemke DA, Liu S. Modified look-locker inversion recovery T1 mapping indices: assessment of accuracy and reproducibility between magnetic resonance scanners. J Cardiovasc Magn Reson 2013; 15:64. 15 White SK, Sado DM, Fontana M, Banypersad SM, Maestrini V, Flett AS, Piechnik SK, Robson MD, Hausenloy DJ, Sheikh AM, Hawkins PN, Moon JC. T1 Mapping for Myocardial Extracellular Volume measurement by CMR: Bolus Only Versus Primed Infusion Technique, 2013 Apr 5 [Epub ahead of print]. 16 Schelbert EB, Testa SM, Meier CG, Ceyrolles WJ, Levenson JE, Blair AJ, Kellman P, Jones BL, Ludwig DR, Schwartzman D, Shroff SG, Wong TC. Myocardial extravascular extracellular volume fraction measurement by gadolinium cardiovascular magnetic resonance in humans: slow infusion versus bolus. J Cardiovasc Magn Reson 2011, Mar 4;13-16. 17 Flacke SJ, Fischer SE, Lorenz CH. Measurement of the gadopentetate dimeglumine partition coefficient in human myocardium in vivo: normal distribution and elevation in acute and chronic infarction. Radiology 2001;218:703-10. 18 Banypersad SM, Sado DM, Flett AS, Gibbs SDG, Pinney JH, Maestrini V, Cox AT, Fontana M, Whelan CJ, Wechalekar AD, Hawkins PN, Moon JC. Quantification of myocardial extracellular volume fraction in systemic AL amyloi-dosis: An Equilibrium Contrast Cardio-vascular Magnetic Resonance Study. Circ Cardiovasc Imaging 2013;6:34-39. 19 Ugander M, Oki AJ, Hsu LY, Kellman P, Greiser A, Aletras AH, Sibley CT, Chen MY, Bandettini WP, Arai AE. Extracellular volume imaging by magnetic resonance imaging provides insights into overt and sub-clinical myocardial pathology. Eur Heart J 2012; 33: 1268–1278. 20 Liu CY, Chang Liu Y, Wu C, Armstrong A, Volpe GJ, van der Geest RJ, Liu Y, Hundley WG, Gomes AS, Liu S, Nacif M, Bluemke DA, Lima JAC. Evaluation of age related interstitial myocardial fibrosis with Cardiac Magnetic Resonance Contrast-Enhanced T1 Mapping in the Multi-ethnic Study of Atherosclerosis (MESA). J Am Coll Cardiol 2013 Jul 3 [Epub ahead of print]. 21 Wong TC, Piehler K, Meier CG, Testa SM, Klock AM, Aneizi AA, Shakesprere J, Kellman P, Shroff SG, Schwartzman DS, Mulukutla SR, Simon MA, Schelbert EB. Association between extracellular matrix expansion quantified by cardiovascular magnetic resonance and short-term mortality. Circulation 2012 Sep 4;126(10):1206-16. 22 Wong TC, Piehler KM, Kang IA, Kadakkal A, Kellman P, Schwartzman DS, Mulukutla SR, Simon MA, Shroff SG, Kuller LH, Schelbert EB. Myocardial extracellular volume fraction quantified by cardiovas-cular magnetic resonance is increased in diabetes and associated with mortality and incident heart failure admission. Eur Heart J 2013 Jun 11 [Epub ahead of print]. 23 Giri S, Chung YC, Merchant A, Mihai G, Rajagopalan S, Raman SV, Simonetti OP. T2 quantification for improved detection of myocardial edema. J Cardiovasc Magn Reson 2009; 11:56. 24 Verhaert D, Thavendiranathan P, Giri S, Mihai G, Rajagopalan S, Simonetti OP, Raman SV. Direct T2 Quantification of Myocardial Edema in Acute Ischemic Injury. J Am Coll Cardiol Img 2011;4: 269-78. 25 Ugander M, Bagi PS, Oki AB, Chen B, Hsu LY, Aletras AH, Shah S, Greiser A, Kellman P, Arai AE. Myocardial oedema as detected by Pre-contrast T1 and T2 CMR delineates area at risk associated with acute myocardial infarction. J Am Coll Cardiol Img 2012;5:596–603. 26 ThavendiranathanP, Walls M, Giri S, Verhaert D, Rajagopalan S, Moore S, Simonetti OP, Raman SV. Improved detection of myocardial involvement in acute inflammatory cardiomyopathies using T2 Mapping. Circ Cardiovasc Imaging 2012;5:102-110. 27 Usman AA, Taimen K, Wasielewski M, McDonald J, Shah S, Shivraman G, Cotts W, McGee E, Gordon R, Collins JD, Markl M, Carr JC. Cardiac Magnetic Resonance T2 Mapping in the monitoring and follow-up of acute cardiac transplant rejection: A Pilot Study. Circ Cardiovasc Imaging. 2012; 6:782-90. 120 ms 0 ms 8 MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world Reprinted from MAGNETOM Flash 5/2013 Reprinted from MAGNETOM Flash 5/2013 MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world 9
- 6. Myocardial T1 Mapping: Techniques and Clinical Applications Juliano Lara Fernandes1; Ralph Strecker2; Andreas Greiser3; Jose Michel Kalaf1 1 Radiologia Clinica de Campinas; University of Campinas, Brazil 2 Healthcare MR, Siemens Ltda, Sao Paulo, Brazil 3 MR Cardiology, Siemens Healthcare, Erlangen, Germany Introduction Cardiovascular magnetic resonance (CMR) has been an increasingly used imaging modality which has experi-enced significant advancements in the last years [1]. One of the most used techniques that have made CMR so important is late gadolinium enhancement (LGE) and the demon-stration of localized areas of infarct and scar tissue [2–4]. However, despite being very sensitive to small areas of regional fibrosis, LGE tech-niques are mostly dependent on the comparison to supposedly normal reference areas of myocardium, thus not being able to depict more diffuse disease. Myocardial interstitial fibrosis, with a diffuse increase in collagen content in myocardial volume, develops as a result of many different stimuli includ- 1A 1B 1C MOLLI images (1A) with respective signal-time curves (1B) and reconstructed T1 map (1C) at 3T. The mean T1 time for this patient was 1152 ms (pre-contrast). 1 Cardiology Clinical Table 1: Comparison of the MOLLI sequences available for T1 mapping Sequence Original MOLLI T1 sequence [15] Optimized MOLLI sequence [17] Shortened MOLLI sequence [18] Preparation Non-selective inversion recovery Non-selective inversion recovery Non-selective inversion recovery Bandwidth 1090 Hz/px 1090 Hz/px 1090 Hz/px Flip angle 50° 35° 35° Base matrix 240 192 192 Phase resolution 151 128 144 FOV × % phase 380 × 342 256 × 100 340 × 75 TI 100 ms 100 ms 100 ms Slice thickness 8 mm 8 mm 8 mm Acquisition window 191.1 ms 202 ms 206 ms Trigger delay 300 ms 300 ms 500 ms Inversions 3 3 3 Acquisition heartbeats 3,3,5 3,3,5 5,5,1 Recovery heartbeats 3,3,1 3,3,1 1,1,1 TI increment 100–150 ms 80 ms 80 ms Scan time 17 heartbeats 17 heartbeats 9 heartbeats Spatial resolution 2.26 × 1.58 × 8 mm 2.1 × 1.8 × 8 mm 1.8 × 1.8 × 8 mm MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world 11 Clinical Cardiology 10 MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world Reprinted from MAGNETOM Flash 1/2012 Reprinted from MAGNETOM Flash 1/2012
- 7. Clinical Cardiology Cardiology Clinical 2A 2B 3A 3B curves and map are shown in Figure 1. One disadvantage of this implementa-tion of MOLLI is its dependence on heart rate, mostly true for T1 values less than 200 msec or greater than 750 msec. However, because the devi-ation is systematic, raw values can be corrected using the formula T1corrected = T1raw – (2.7 × [heart rate -70]), bring-ing the coefficient of variation down to 4.6% after applying the correction. An optimized MOLLI sequence was subsequently described where heart rate correction might not be even nec-essary [17]. In the optimized sequence, the authors tested variations in readout flip angle, minimum inversion time, inversion time increments and number of pauses between each readout sequence. The conclusion from these experiments showed that a flip angle of 35°, a minimum inversion time of 100 msec, increments of 80 msec and three heart cycle pauses allowed for the most accurate measurement of myocardial T1 (Table 1). Because T1 assessment may be sensitive to motion artifacts and not all patients might be able to hold their breaths through-out all the necessary cardiac cycles used in MOLLI’s sequence implemen-tation, more recently a shortened version sequence (ShMOLLI) using only 9 heart beats was presented to account for those limitations [18]. Using incomplete recovery of the lon-gitudinal magnetization that is cor-rected directly in the scanner by conditional interpretation, ShMOLLI was directly compared to MOLLI in patients over a wide range of T1 times and heart rates both at 1.5 and 3T. The results showed that despite an increase in noise and slight increase in the coefficient of variation (espe-cially at 1.5T), T1 times were not sig-nificantly different using ShMOLLI with the advantage of much shorter acquisition times (9.0 ± 1.1 sec versus 17.6 ± 2.9 sec). An example of MOLLI and ShMOLLI images from the same patient is presented in Figure 2. Up to now, after acquiring images for T1 mapping, one had to analyze them using in-house developed soft-ware, dedicated commercial pro-grams or open-source solutions [19], not always a simple and routine task, leading to difficulty in post-process-ing the data and generating T1 values. Recent advances have provided new inline processing techniques that will generate the T1 maps automatically after image acquisition with MOLLI, without the need for further post-pro-cessing, accelerating the whole pro-cess. An example of such automated T1 map is presented in Figure 3. At the same time, inline application of motion correction permits more accu-rate pixel-wise maps, avoiding errors due to respiratory deviations. An example of an image with and with-out motion correction is presented in Figure 4. Clinical applications Potentially, T1 mapping can be used to assess any disease that affects the myocardium promoting diffuse fibro-sis. However, because of its recent MOLLI (2A) versus ShMOLLI (2B) in a single patient at 3T post-contrast. The calculated values for the 11 MOLLI images were 551 ms versus 544 ms for the 8 images of the shMOLLI set. The time to acquire the MOLLI images were 21 seconds versus 14 seconds for the shMOLLI sequence (with a patient heart rate of 61 bpm). ing pressure overload, volume overload, aging, oxidative stress and activation of the sympathetic and renin-angiotensin-aldosterone sys-tem [5]. Different from replacement fibrosis, where regional collagen deposits appear in areas of myocyte injury, LGE has a limited sensitivity for interstitial diffuse fibrosis [6]. Therefore, if one wants to image dif-fuse interstitial fibrosis within the myocardium other techniques might be more suitable. While echocardiogram backscatter and nuclear imaging techniques may be applied for that purpose [7, 8], myocardial tissue characterization is definitely an area where CMR plays a large role. While equilibrium contrast CMR and myocardial tagging have been shown to reflect diffuse myocardial fibrosis, T1 mapping techniques have been most widely used. In the follow-ing, we describe the developments in T1 mapping as well as their possible current and future uses. T1 mapping By directly quantifying T1 values for each voxel in the myocardium, a parametric map can be generated representing the T1 relaxation times of any region of the heart without the need to compare it to a normal reference standard before or after the use of a contrast agent. The first attempts to measure T1 times in the myocardium used the original Look- Locker sequence and were done using free breathing with acquisition times of over 1 minute per image [9, 10], not allowing for pixel-based-mapping but only for regions-of-interest analy-sis. Another implementation of T1 mapping used variable sampling of the k-space in time (VAST), acquir-ing images in three to four breath-holds and correlating that data to invasive biopsy [11]. Other sequences have been used for quantification of T1 as well using inversion recovery TrueFISP [12, 13] or multishot satura-tion recovery images [14] but their reproducibility and accuracy have not been extensively validated. The most widely used T1 mapping sequence is based on the Modified Look-Locker Inversion-recovery (MOLLI) technique. Described originally by Messroghli et al. [15] it consists of a single shot TrueFISP image with acqui-sitions over different inversion time readouts allowing for magnetization recovery of a few seconds after 3 to 5 readouts. The parameters for the original MOLLI sequence are described in Table 1. The advantages of this sequence over previous methods are its acquisition in only one relatively short breath-hold, the higher spatial resolution (1.6 × 2.3 × 8 mm) and increased dynamic signal. Reproduc-ibility studies using this sequence have shown that the method is very accu-rate with a coefficient of variation of 5.4% [16] although an underestima-tion of 8% should be expected based on phantom data. An example of MOLLI images and its respective signal-time 2 An example of an automated T1 map generated on the fly with inline processing after acquisition of a MOLLI sequence at 3T. In (3A) the original images acquired and in (3B) the inline map. The T1 for this patient was calculated at 525 ms post-contrast. 3 12 MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world Reprinted from MAGNETOM Flash 1/2012 Reprinted from MAGNETOM Flash 1/2012 MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world 13
- 8. Clinical Cardiology Cardiology Clinical development, the technique has only been evaluated on a small number of patients although the clinical scenar-ios are varied. The first clinical description of direct T1 mapping in pathological situa-tions was done in patients with acute myocardial infarction [20]. While the authors did not use the described MOLLI sequence, they did note that pre-contrast infarct areas had an 18 ± 7% increase in T1 times com-pared to normal myocardium and that after contrast the same areas showed a 27 ± 4% reduction compared to non-infarcted areas (P < 0.05 for both). In chronic myocardial infarction, where LGE has proven so useful, these changes were also observed although differences were not as pronounced as in the acute setting [21]. In amyloidosis, post-contrast T1 times were also detected to be shorter in the subendocardial regions compared to other myocardium areas [22]. The combination of both LGE identifica-tion and T1 times < 191 msec in the subendocardium at 4 minutes pro-vided a 97% concordance in diagnosis of cardiac amyloidosis and T1 values significantly correlated to markers of amyloid load such as left ventricular mass, wall thickness, interatrial thick-ness and diastolic function. In valve disease, an attempt to show differences in T1 values in patients with chronic aortic regurgitation using MOLLI sequence did not find any changes in the overall group before or after contrast [23]. However, the authors did notice that differences were observed regionally in segments that demonstrated impaired wall motion in cine images. The small num-ber of patients (n = 8) in the study might have affected the conclusions and further evaluation of similar data might yield other conclusions. A more recent study showed that, using equi-librium contrast CMR, diffuse fibrosis measured in aortic stenosis patients provided significant correlations to quantification on histology [24]. In heart failure, the use of T1 map-ping has been more widely studied and directly correlated to histology evaluation [11]. In this paper, the authors evaluated patients with isch-emic, idiopathic and restrictive car-diomyopathies showing that post-contrast T1 times at 1.5T were significantly shorter than controls even after exclusion of areas of LGE (429 ± 22 versus 564 ± 23 msec, P < 0.0001). We have investigated a similar group of patients on a 3T MAGNETOM Verio scanner and have found that both dilated and hypertro-phic cardiomyopathy patients have lower post-contrast T1 times com-pared to controls, but non-infarcted areas from ischemic cardiomyopathy patients do not show significant differences (unpublished data). Examples of a myocardial T1 map at 3T from a patient with dilated cardio-myopathy and suspected hypertro-phic cardiomyopathy are seen in Fig-ure 5 and 6 respectively. Finally, in patients with both type 1 and 2 diabetes melitus, T1 mapping using CMR was able to show that these patients may have increased interstitial fibrosis compared to controls as T1 times were significantly shorter (425 ± 72 msec versus 504 ± 34 msec, P < 0.001) and correlated to global longitudinal strain by echocardiography, demonstrating impaired myocardial systolic function. Future directions Certainly with the research of T1 mapping in different clinical scenarios the applicability of the method will increase substantially. In the mean-time, more effort has been made to further standardize values across dif-ferent patients and time points. As T1 time, especially after injection of con-trast, depends on both physiologic and scan acquisitions, methods have been described to account for these factors, with normalization of T1 values [25]. More than that, standardization of normal values across a larger number of normal individuals is also necessary since most papers provide data on much reduced cohorts, mostly limited to single center data. In that regard, a large multicenter registry is already collecting data at 3T in patients from 20 to 80 years of age in Latin America [Fernandes JL et al. – www.clinicaltri-als. gov – NCT01030549]. Besides that, other techniques are under develop-ment that might allow T1 measurement with larger coverage of the heart using 3D methods [26]. Nevertheless, with the current tech-niques available there are already much more clinical applications to explore and certainly quantitative T1 mapping will become one of the key applica-tions in CMR in the near future. 4A 4B 4 Example of a MOLLI sequence obtained without (4A) and with (4B) motion correction. Notice the deviation from baseline of the left ventricle during the image acqui-sition cycle, fully corrected in (4B). References 1 Fernandes JL, Pohost GM. Recent advances in cardiovascular magnetic resonance. Rev Cardiovasc Med 2011;12:e107-12. 2 Kim RJ, Wu E, Rafael A, et al. The use of contrast-enhanced magnetic resonance imaging to identify reversible myocardial dysfunction. N Engl J Med 2000;343: 1445-53. 3 Assomull RG, Prasad SK, Lyne J, et al. Cardiovascular magnetic resonance, fibrosis, and prognosis in dilated cardiomy-opathy. J Am Coll Cardiol 2006;48: 1977-85. 4 Ordovas KG, Higgins CB. Delayed contrast enhancement on MR images of myocardium: past, present, future. Radiology 2011;261:358-74. 5 Jellis C, Martin J, Narula J, Marwick TH. Assessment of nonischemic myocardial fibrosis. J Am Coll Cardiol 2010;56:89-97. 6 Mewton N, Liu CY, Croisille P, Bluemke D, Lima JA. Assessment of myocardial fibrosis with cardiovascular magnetic resonance. J Am Coll Cardiol 2011;57:891-903. 7 Picano E, Pelosi G, Marzilli M, et al. In vivo quantitative ultrasonic evaluation of myocardial fibrosis in humans. Circulation 1990;81:58-64. 17 Messroghli DR, Greiser A, Frohlich M, Dietz R, Schulz-Menger J. Optimization and validation of a fully-integrated pulse sequence for modified look-locker inversion-recovery (MOLLI) T1 mapping of the heart. J Magn Reson Imaging 2007;26:1081-6. 18 Piechnik SK, Ferreira VM, Dall’Armellina E, et al. Shortened Modified Look-Locker Inversion recovery (ShMOLLI) for clinical myocardial T1 mapping at 1.5 and 3 T within a 9 heartbeat breathhold. J Cardiovasc Magn Reson 2010;12:69. 19 Messroghli DR, Rudolph A, Abdel-Aty H, et al. An open-source software tool for the generation of relaxation time maps in magnetic resonance imaging. BMC Med Imaging 2010; 10:16. 20 Messroghli DR, Niendorf T, Schulz- Menger J, Dietz R, Friedrich MG. T1 mapping in patients with acute myocardial infarction. J Cardiovasc Magn Reson 2003;5:353-9. 21 Messroghli DR, Walters K, Plein S, et al. Myocardial T1 mapping: appli-cation to patients with acute and chronic myocardial infarction. Magn Reson Med 2007;58:34-40. 22 Maceira AM, Joshi J, Prasad SK, et al. Cardiovascular magnetic resonance in cardiac amyloidosis. Circulation 2005;111:186-93. 23 Sparrow P, Messroghli DR, Reid S, Ridgway JP, Bainbridge G, Sivana-nthan MU. Myocardial T1 mapping for detection of left ventricular myocardial fibrosis in chronic aortic regurgitation: pilot study. AJR Am J Roentgenol 2006;187:W630-5. 24 Flett AS, Hayward MP, Ashworth MT, et al. Equilibrium contrast cardiovas-cular magnetic resonance for the measurement of diffuse myocardial fibrosis: preliminary validation in humans. Circulation 2010; 122:138-44. 8 van den Borne SW, Isobe S, Verjans JW, et al. Molecular imaging of interstitial alterations in remodeling myocardium after myocardial infarction. J Am Coll Cardiol 2008;52:2017-28. 9 Flacke SJ, Fischer SE, Lorenz CH. Measurement of the gadopentetate dimeglumine partition coefficient in human myocardium in vivo: normal distribution and elevation in acute and chronic infarction. Radiology 2001;218:703-10. 10 Brix G, Schad LR, Deimling M, Lorenz WJ. Fast and precise T1 imaging using a TOMROP sequence. Magn Reson Imaging 1990;8:351-6. 11 Iles L, Pfluger H, Phrommintikul A, et al. Evaluation of diffuse myocardial fibrosis in heart failure with cardiac magnetic resonance contrast-enhanced T1 mapping. J Am Coll Cardiol 2008;52: 1574-80. 12 Schmitt P, Griswold MA, Jakob PM, et al. Inversion recovery TrueFISP: quantifi-cation of T(1), T(2), and spin density. Magn Reson Med 2004;51:661-7. 13 Bokacheva L, Huang AJ, Chen Q, et al. Single breath-hold T1 measurement using low flip angle TrueFISP. Magn Reson Med 2006;55:1186-90. 14 Wacker CM, Bock M, Hartlep AW, et al. Changes in myocardial oxygenation and perfusion under pharmacological stress with dipyridamole: assessment using T*2 and T1 measurements. Magn Reson Med 1999;41:686-95. 15 Messroghli DR, Radjenovic A, Kozerke S, Higgins DM, Sivananthan MU, Ridgway JP. Modified Look-Locker inversion recovery (MOLLI) for high-resolution T1 mapping of the heart. Magn Reson Med 2004;52: 141-6. 16 Messroghli DR, Plein S, Higgins DM, et al. Human myocardium: single-breath-hold MR T1 mapping with high spatial resolution--reproducibility study. Radiology 2006;238:1004-12. Reprinted from MAGNETOM Flash 1/2012 Reprinted from MAGNETOM Flash 1/2012 14 MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world 15
- 9. Clinical Cardiology T1 mapping at 3T after contrast of a patient with (5A) dilated cardiomyopathy (T1 of 507 ms) in comparison to (5B) a control patient (T1 of 615 ms). 6A 6B T1 mapping of a patient with (6A) suspected hypertrophic cardiomyopathy (T1 of 466 ms) in comparison to (6B) a control patient (with a T1 of 615 ms). Contact Juliano L Fernandes R. Antonio Lapa 1032 Campinas-SP – 13025-292 Brazil Phone: +55-19-3579-2903 Fax: +55-19-3252-2903 jlaraf@fcm.unicamp.br 5A 5B 5 6 25 Gai N, Turkbey EB, Nazarian S, et al. T1 mapping of the gadolinium-enhanced myocardium: adjustment for factors affecting interpatient comparison. Magn Reson Med 2011;65:1407-15. 26 Coolen BF, Geelen T, Paulis LE, Nauerth A, Nicolay K, Strijkers GJ. Three-dimensional T1 mapping of the mouse heart using variable flip angle steady-state MR imaging. NMR Biomed 2011;24:154-62. 16 MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world Reprinted from MAGNETOM Flash 1/2012 www.siemens.com/cmr syngo.MR Cardiac Perfusion* provides interactive colored pixel maps for real-time dynamic analysis Your benefits 1. Complements the MR Cardiac Reading workflow 2. Enables you to specifically synchronize rest- and stress-perfusion series 3. Simplifies visual assessment of perfusion defects due to Siemens unique “HeartFreeze” Motion Correction This feature is currently under development; it is not for sale in the U.S. and all other countries. Its future availability cannot be guaranteed. * Answers for life.
- 10. Clinical Cardiovascular Imaging Cardiovascular Imaging Clinical Preliminary Experiences with Compressed Sensing Multi-Slice Cine Acquisitions for the Assessment of Left Ventricular Function: CV_sparse WIP G. Vincenti, M.D.1; D. Piccini2,4; P. Monney, M.D.1; J. Chaptinel3; T. Rutz, M.D.1; S. Coppo3; M. O. Zenge, Ph.D.4; M. Schmidt4; M. S. Nadar5; Q. Wang5; P. Chevre1, 6; M.; Stuber, Ph.D.3; J. Schwitter, M.D.1 1 Division of Cardiology and Cardiac MR Center, University Hospital of Lausanne (CHUV), Lausanne, Switzerland 2 Advanced Clinical Imaging Technology, Siemens Healthcare IM BM PI, Lausanne, Switzerland 3 Department of Radiology, University Hospital (CHUV) and University of Lausanne (UNIL) / Center for Biomedical Imaging (CIBM), Lausanne, Switzerland 4 MR Applications and Workflow Development, Healthcare Sector, Siemens AG, Erlangen, Germany 5 Siemens Corportate Technology, Princeton, USA 6 Department of Radiology, University Hospital Lausanne, Switzerland ize pathological myocardial tissue was the basis to assign a class 1 indication for patients with known or suspected heart failure to undergo CMR in the new Heart Failure Guidelines of the European Society of Cardiology [3]. decision making [3] e.g. to start [4] or stop [5] specific drug treatments or to implant devices [6]. CMR is generally accepted as the gold stan-dard method to yield most accurate measures of LV ejection fraction and LV volumes. This capability and the additional value of CMR to character- Introduction Left ventricular (LV) ejection fraction is one of the most important measures in cardiology and part of every car-diac imaging evaluation as it is recog-nized as one of the strongest predic-tors of outcome [1]. It allows to assess the effect of established or novel treatments [2], and it is crucial for The evaluation of LV volumes and LV ejection fraction are based on well-defined protocols [7] and it involves the acquisition of a stack of LV short axis cine images from which volumes are calculated by applying Simpson’s rule. These stacks are typically acquired in multiple breath-holds. Quality crite-ria [8] for these functional images are available and are implemented e.g. for the quality assessment within the European CMR registry which currently holds approximately 33,000 patients and connects 59 centers [9]. Recently, compressed sensing (CS) techniques emerged as a means to considerably accelerate data acquisi-tion without compromising signifi-cantly image quality. CS has three requirements: 1) transform sparsity, 2) incoherence of undersampling artifacts, and 3) nonlinear reconstruction (for details, see below). Based on these prerequisites, a CS approach for the acquisition of cardiac cine images was developed and tested*. In particular, the potential to acquire several slices covering the heart in different orientations within a single breath-hold would allow to apply model-based analysis tools which theoretically could improve the motion assessment at the base of the heart, where considerable through-plane motion on short-axis slices can introduce substantial errors in LV volume and LV ejection fraction cal-culations. Conversely, with a multi-breath- hold approach, there are typi-cally small differences in breath-hold positions which can introduce errors in volume and function calculations. The pulse sequence tested here allows for the acquisition of 7 cine slices within 14 heartbeats with an excellent temporal and spatial resolution. Such a pulse sequence would also offer the advantage to obtain func-tional information in at least a single plane in patients unable to hold their breath for several heartbeats or in patients with frequent extrasystoles or atrial fibrillation. However, it should be mentioned that accurate quantita-tive measures of LV volumes and function cannot be obtained in highly arrhythmic hearts or in atrial fibrilla-tion, as under such conditions vol-umes and ejection fraction change from beat to beat due to variable fill-ing conditions. Nevertheless, rough estimates of LV volumes and function would still be desirable in arrhythmic patients. In a group of healthy volunteers and patients with different LV patholo-gies, the novel single-breath-hold CS cine approach was compared with the standard multi-breath-hold cine technique with respect to measure LV volumes and LV ejection fraction. The CV_sparse work-in-progress (WIP) The CV_sparse WIP package imple-ments sparse, incoherent sampling and iterative reconstruction for car-diac applications. This method in principle allows for high acceleration factors which enable triggered 2D real-time cine CMR while preserving high spatial and/or temporal resolu-tion of conventional cine acquisi-tions. Compressed sensing methods exploit the potential of image com-pression during the acquisition of raw input data. Three components [10] are crucial for the concept of compressed sensing to work I. Sparsity: In order to guarantee compressibility of the input data, sparsity must be present in a specific transform domain. Sparsity can be computed e.g. by calculating differ-ences between neighboring pixels or by calculating finite differences in angiograms which then detect pri-marily vessel contours which typically 1 * Work in progress: The product is still under development and not commercially available yet. Its future availability cannot be ensured. 1 Display of the represent a few percent of the planning of the 7 slices (4 short axis and 3 long axis slices) acquired within a single breath-hold with the three localizers. 1 2A 2B Displays of the data analysis tools for the conventional short axis stack of cine images covering the entire LV (2A) and the 4D analysis tool (2B), which is model-based and takes long axis shortening of the LV, i.e. mitral annulus motion into account. Note that with both analysis tools, LV trabeculations are included into the LV volume, particularly in the end-diastolic images (corresponding images on the left of top row in 2A and 2B). 2 18 MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world Reprinted from MAGNETOM Flash 5/2013 Reprinted from MAGNETOM Flash 5/2013 MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world 19
- 11. Clinical Cardiovascular Imaging Cardiovascular Imaging Clinical entire image data only. Furthermore, sparsity is not limited to the spatial domain: the acquisition of cine images of the heart can be highly sparsified in the temporal dimension. II. Incoherent sampling: The alias-ing artifacts due to k-space unders-ampling must be incoherent, i.e. noise-like, in that transform domain. Here, it is to mention that fully ran-dom k-space sampling is suboptimal as k-space trajectories should be smooth for hardware and physiologi-cal considerations. Therefore, inco-herent sampling schemes must be designed to avoid these concerns while fulfilling the condition of ran-dom, i.e. incoherent sampling. III. Reconstruction: A non-linear iter-ative optimization corrects for sub-sampling artifacts during the process of image reconstruction yielding to a best solution with a sparse representation in a specific transform domain and which is consistent with the input data. Such compressed sensing techniques can also be com-bined with parallel imaging tech-niques [11]. WIP CV_sparse Sequence The current CV_sparse sequence [12] realizes incoherent sampling by initially distributing the readouts pseudo-randomly on the Cartesian grid in k-space. In addition, for cine-CMR imaging, a pseudo-random offset is applied from frame-to-frame which results in an incoherent tem-poral jitter. Finally, a variable sam-pling density in k-space stabilizes the iterative reconstruction. To avoid eddy current effects for balanced steady-state free precession (bSSFP) acquisitions, pairing [13] can also be applied. Thus, the tested CV_sparse sequence is characterized by sparse, incoherent sampling in space and time, non-linear iterative reconstruc-tion integrating SENSE, and L1 wave-let regularization in the phase encod-ing direction and/or the temporal dimension. With regard to reconstruc-tion, the ICE program runs a non-linear iterative reconstruction with k-t regularization in space and time specifically modified for compressed sensing. The algorithm derives from a parallel imaging type reconstruc-tion which takes coil sensitivity maps into account, thus supporting pre-dominantly high acceleration factors. For cine CMR, no additional reference scans are needed because – similar to TPAT – the coil sensitivity maps are calculated from the temporal average of the input data in a central region of k-space consisting of not more than 48 reference lines. The exten-sive calculations for image recon-struction typically running 80 itera-tions are performed online on all CPUs on the MARS computer in paral-lel, in order to reduce reconstruction times. Volunteer and Patient studies In order to obtain insight into the image quality of single-breath-hold multi-slice cine CMR images acquired with the compressed sensing (CS) approach, we studied a group of healthy volunteers and a patient group with different pathologies of the left ventricle. In addition to the evaluation of image quality, the robustness and the precision of the CS approach for LV volumes and LV ejection fraction was also assessed in comparison with a standard high-resolution cine CMR approach. All CMR examinations were performed on a 1.5T MAGNETOM Aera (Siemens Healthcare, Erlangen, Germany). The imaging protocol consisted of a set of cardiac localizers followed by the acquisition of a stack of conventional short-axis SSFP cine images covering the entire LV with a spatial and tem-poral resolution of 1.2 x 1.6 mm2, and approximately 40 ms, respectively (slice thickness: 8 mm; gap between slices: 2 mm). LV 2-chamber, 3-cham-ber, and 4-chamber long-axis acquisi-tions were obtained for image quality assessment but were not used for LV volume quantifications. As a next step, to test the new CS-based technique, slice orientations were planned to cover the LV with 4 short-axis slices distrib-uted evenly over the LV long axis com-plemented by 3 long-axis slices (i.e. a 2-chamber, 3-chamber, and 4-chamber slice) (Fig. 1). These 7 slices were then acquired in a single breath-hold maneuver lasting 14 heart beats (i.e. 2 heart beats per slice) resulting in an acceleration factor of 11.0 with a tem-poral and spatial resolution of 30 ms and 1.5 x 1.5 mm2, respectively (slice thickness: 6 mm). As the reconstruc-tion algorithm is susceptible to aliasing in the phase-encoding direction, the 7 slices were first acquired with a non-cine acquisition to check for correct phase-encoding directions and, if needed, to adjust the field-of-view to avoid fold-over artifacts. After confirmation of correct imaging parameters, the 7-slice single-breath- hold cine CS-acquisition was performed. In order to obtain a refer-ence for the LV volume measurement, a phase-contrast flow measurement in the ascending aorta was per-formed to be compared with the LV stroke volumes calculated from the standard and CS cine data. The conventional stack of cine SSFP images was analyzed by the Argus software (Siemens Argus 4D Ventric-ular Function, Fig. 2A). The CS cine data were analyzed by the 4D-Argus software (Siemens Argus, Fig. 2B). Such software is based on an LV model and, with relatively few opera-tor interactions, the contours for the LV endocardium and epicardium are generated by the analysis tool. Of note, this 4D analysis tool automati-cally tracks the 3-dimensional motion of the mitral annulus throughout the cardiac cycle which allows for an accurate volume calculation particu-larly at the base of the heart. Results and discussion Image quality – robustness of the technique Overall, a very good image quality of the single-breath-hold multi-slice CS acquisitions was obtained in the 12 volunteers and 14 patient studies. All CS data sets were of adequate quality to undergo 4D analysis. Small structures such as trabeculations were visualized in the CS data sets as shown in Figures 3 and 4. However, very small structures, detectable by the conventional cine acquisitions, were less well discernible by the CS images. Therefore, it should be men-tioned here, that this accelerated single- breath-hold CS approach would be adequate for functional measure-ments, i.e. LV ejection fraction assessment (see also results below), whereas assessment of small struc-tures as present in many cardiomyop-athies is more reliable when per-formed on conventional cine images. Temporal resolution of the new tech-nique appears adequate to even detect visually the dyssynchroneous contraction pattern in left bundle branch block. Also, the image con-trast between the LV myocardium and the blood pool was high on the CS images allowing for an easy assessment of the LV motion pattern. As a result, the single-breath-hold cine approach permits to reconstruct the LV in 3D space with high tempo-ral resolution as illustrated in Figure 5. Since these data allow to correctly include the 3D motion of the base of the heart during the cardiac cycle, the LV stroke volume appears to be measurable by the CS approach with higher accuracy than with the con-ventional multi-breath-hold approach (see results below). With an accurate measurement of the LV stroke vol-ume, the quantification of a mitral insufficiency should theoretically ben-efit (when calculating mitral regurgi-tant volume as ‘LV stroke volume minus aortic forward-flow volume’). As a current limitation of the CS approach, its susceptibility for fold-over artifacts should be mentioned (Figs. 6A). Therefore, the field-of-view must cover the entire anatomy and thus, some penalty in spatial res- Standard cine 9 heartbeats CV_SPARSE 3 heartbeats CV_SPARSE 2 heartbeats CV_SPARSE 1 heartbeat Examples of visualization of small trabecular structures in the LV (in the rectangle) with the standard cine SSFP sequence (image on the left) and the accelerated compressed sensing sequences (images on the right). Despite increasing acceleration most infor-mation on small intraluminal structures remains visible. 3 RCA Example demonstrating the performance of the compressed sensing technique visualizing small structures such as the right coronary artery (RCA) with high temporal and spatial resolution acquired within 2 heart-beats. Short-axis view of the base of the heart (1 out of 17 frames). 4 3 4 20 MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world Reprinted from MAGNETOM Flash 5/2013 Reprinted from MAGNETOM Flash 5/2013 MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world 21
- 12. Clinical Cardiovascular Imaging Cardiovascular Imaging Clinical olution may occur in relation to the patient’s anatomy. In addition, the sparsity in the temporal domain may be limited in anatomical regions of very high flow, and therefore, in some acquisitions, flow-related arti-facts occurred in the phase-encoding direction during systole (Figs. 6B, C). Also, in its current version, the sequence is prospective, thus it does not cover the very last phases of the cardiac cycle and the reconstruction times for the CS images lasted sev-eral minutes precluding an immediate assessment of the image data quality or using this image information to plan next steps of a CMR examination. Performance of the single-breath- hold CS approach in comparison with the stan-dard multi-breath-hold cine approach From a quantitative point-of-view, the accurate and reliable measure-ment of LV volumes and function is crucial as many therapeutic decisions directly depend on these measures [3–6]. In this current relatively small study group, LV end-diastolic and end-systolic volumes measured by the single-breath-hold CS approach were comparable with those calcu-lated from the standard multi-breath-hold cine SSFP approach. LVEDV and LVESV differed by 10 ml ± 17 ml and 2 ml ± 12 ml, respectively. Most impor-tantly, LV ejection fraction differed by only 1.3 ± 4.7% (50.6% vs 49.3% for multi-breath-hold and single-breath-hold, respectively, p = 0.17; regres-sion: r = 0.96, p < 0.0001; y = 0.96x + 0.8 ml). Thus, it can be concluded that the single-breath-hold CS approach could potentially replace the multi-breath- hold standard technique for the assessment of LV volumes and systolic function. What about the accuracy of the novel single-breath-hold CS technique? To assess the accuracy of the LV vol-ume measurements, LV stroke volume was compared with the LV output measured in the ascending aorta with phase-contrast MR. As the flow mea-surements were performed distally to the coronary arteries, flow in the coro-naries was estimated as the LV mass multiplied by 0.8 ml/min/g. An excel-lent agreement was found with a mean of 86.8 ml/beat for the aortic flow measurement and 91.9 ml/beat for the LV measurements derived from the single-breath-hold CS data (r = 0.93, p < 0.0001). By Bland-Altman analysis, the stroke volume approach overestimated by 5.2 ml/beat versus the reference flow measurement. For the conventional stroke volume mea-surements, this difference was 15.6 ml/beat (linear regression analysis vs aortic flow: r = 0.69, p < 0.01). More importantly, the CS LV stroke data were not only more precise with a smaller mean difference, the variability of the CS data vs the reference flow data was less with a standard deviation as low as 6.8 ml/beat vs 12.9 ml/beat for the standard multi-breath-hold approach (Fig. 7). Several explanations may apply for the higher accuracy of the single-breath- hold multi-slice CS approach in comparison to the conventional multi-breath- hold approach: 1) With the single-breath-hold approach, all acquired slices are cor-rectly co-registered, i.e. they are cor-rectly aligned in space, a prerequisite for the 4D-analysis tool to work properly. 2) This 4D-analysis tool allows for an accurate tracking of the mitral valve plane motion during the cardiac cycle as shown in Figure 5, which is impor-tant as the cross-sectional area of the heart at its base is large and thus, inac-curate slice positioning at the base of Display of the 3D reconstruction derived from the 7 slices acquired within a single breath-hold. Note the long-axis shortening of the LV during systole allowing for accurate LV volume measurements (5A, 5B, yellow plane). Any orientation of the 3D is available for inspection of function (5A–D). 5 6A A typical fold-over artifact along the phase-encoding direction in a short axis slice, oriented superior-inferior for demonstrative purpose. 6B No flow-related artifacts are visible on the end-diastolic phases, while small artifacts in phase-encoding direction (Artif, arrows) occur in mid-systole projecting over the mitral valve (6C). 5A 5B 5C 5D 6A 6B 6C Artif Artif 22 MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world Reprinted from MAGNETOM Flash 5/2013 Reprinted from MAGNETOM Flash 5/2013 MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world 23
- 13. Clinical Cardiovascular Imaging Cardiovascular Imaging Clinical 50 60 70 120 130 130 120 110 100 90 80 70 the heart with conventional short-axis slices typically translate in relatively large errors. Nevertheless, we observed a systematic overesti-mation of the stroke volume by the CS approach of 5.2 ml/beat in com-parison to the flow measurements. In normal hearts with tricuspid aortic valves, an underestimation of aortic flow by the phase-contrast technique is very unlikely [14]. Thus, overesti-mation of stroke volume by the volume approach is to consider. In the vol-ume contours, the papillary muscles are excluded as illustrated in Figure 8. As these papillary muscles are excluded in both the diastolic and systolic con-tours, this aspect should not affect net LV stroke volume. However, as shown in Figure 8, smaller trabecula-tions of the LV wall are included into the LV blood pool contour in the diastolic phase, while these trabecu-lations, CS technique Standard technique when compacted in the end- systolic phase, are excluded from the blood pool resulting in a small overestimation of the end-diastolic volume, and thus, LV stroke volume. This explanation is likely as Van Rossum et al. demonstrated a slight underestimation of the LV mass when calculated on end-diastolic phases versus end-systolic phases, as trabec-ulations in end-diastole are typically excluded from the LV walls [15]. In summary, this novel very fast acquisition strategy based on a CS technique allows to cover the entire LV with high temporal and spatial resolution within a single breath-hold. The image quality based on these preliminary results appears adequate to yield highly accurate measures of LV volumes, LV stroke volume, LV mass, and LV ejection fraction. 7 Testing of this very fast multi-slice cine approach for the atria and the right ventricle is currently ongoing. Finally, these preliminary data show that com-pressed sensing MR acquisitions in the heart are feasible in humans and compressed sensing might be imple-mented for other important cardiac sequences such as fibrosis/viability imaging, i.e. late gadolinium enhance-ment, coronary MR angiography, or MR first-pass perfusion. The Cardiac MR Center of the University Hospital Lausanne The Cardiac Magnetic Resonance Center (CRMC) of the University Hospital of Lausanne (Centre Hospitalier Universi-taire Vaudois; CHUV) was established in 2009. The CMR center is dedicated to high-quality clinical work-up of car-diac patients, to deliver state-of-the-art training in CMR to cardiologists and radiologists, and to pursue research. In the CMR center education is pro-vided for two specialties while focus-ing on one organ system. Traditionally, radiologists have focussed on using one technique for different organs, while cardiologists have concentrated on one organ and perhaps one tech-nique. Now in the CMR center the focus is put on a combination of spe-cialists with different background on one organ. Research at the CMR center is devoted to four major areas: the study of 1.) cardiac function and tissue charac-terization, specifically to better under-stand diastolic dysfunction, 2.) the development of MR-compatible cardiac devices such as pacemakers and ICDs; 3.) the utilization of hyperpolarized 13C-carbon contrast media to investi-gate metabolism in the heart, and An excellent corre-lation is obtained for the LV stroke volume calculated from the compressed sensing data with the flow volume in the aorta measured by phase-contast technique. Variability of the conventional LV stroke volume data appears higher than for the compressed sensing data. LV stroke volume: comparison vs aortic forward flow LV short-axis slice: CV_SPARSE 4.) the development of 19F-fluorine-based CMR techniques to detect inflammation and to label and track cells non-invasively. For the latter two topics, the CMR center established tight collabora-tions with the Center for Biomedical Imaging (CIBM), a network around Lake Geneva that includes the Ecole Polytechnique Fédérale de Lausanne (EPFL), and the universities and uni-versity hospitals of Lausanne and Geneva. In particular, strong collab-orative links are in place with the CVMR team of Prof. Matthias Stuber, a part of the CIBM and located at the University Hospital Lausanne and with Prof. A. Comment, with whom we perform the studies on real-time metabolism based on the 13C-carbon hyperpolarization (DNP) technique. In addition, collaborative studies are ongoing with the Heart Failure and Cardiac Transplantation Unit led by Prof. R. Hullin (detection of graft rejection by tissue characterization) and the Oncology Department led by Prof. Coukos (T cell tracking by19F- MRI in collaboration with Prof. Stuber, R. van Heeswijk, CIBM, and Prof. O. Michielin, Oncology). This structure allows for a direct interdis-ciplinary interaction between physi-cians, engineers, and basic scientists on a daily basis with the aim to enable innovative research and fast translation of these techniques from bench to bedside. The CMRC is also the center of com-petence for the quality assessment of the European CMR registry which holds currently approximately 33,000 patient studies acquired in 59 centers across Europe. The members of the CRMC team are: Prof. J. Schwitter (director of the center), PD Dr. X. Jeanrenaud, Dr. D. Locca, MER, Dr. P. Monney, Dr. T. Rutz, Dr. C. Sierro, and Dr. S. Koest-ner (cardiologists, staff members), Overestimation of end-diastolic LV volumes by volumetric measurements. In comparison to ejected blood from the LV as measured with phase-contrast techniques, the volumetric measurements of LV stroke volume overestimated by approximately 5 ml, most likely by overestimation of LV end-diastolic volume. Small trabculations (yellow contours in 8A) are included into the LV blood volume (red contour in 8A) in diastole, while these trabeculations (yellow contours in 8B) are typically included in the end-systolic phase (red contours in 8B). For the same reasons, LV mass (= green contour minus red contour) is often slightly underestimated in diastole vs systole. 8 7 8A 8B End-diastolic frame End-systolic frame ml/beat (aortic forward flow by PC) ml/beat (LV stroke volume) 80 90 100 110 60 24 MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world Reprinted from MAGNETOM Flash 5/2013 Reprinted from MAGNETOM Flash 5/2013 MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world 25
- 14. References 1 Curtis JP, Sokol SI, Wang Y, Rathore SS, Ko DT, Jadbabaie F, Portnay EL, Marshalko SJ, Radford MJ, Krumholz HM. The associ-ation of left ventricular ejection fraction, mortality, and cause of death in stable outpatients with heart failure. Journal of the American College of Cardiology. 2003;42(4):736-42. 2 Sürder D, Manka R, Lo Cicero V, Moccetti T, Rufibach K, Soncin S, Turchetto L, Radrizzani M, Astori G, Schwitter J, Erne P, Jamshidi P, Auf Der Maur C, Zuber M, Windecker S, Moschovitis A, Wahl A, Bühler I, Wyss C, Landmesser U, Lüscher T, Corti R. Intracoronary injection of bone marrow derived mononuclear cells, early or late after acute myocardial infarction: Effects on global LV-function: 4 months results of the SWISS-AMI trial. Circulation. 2013;127:1968-79. 11 Liang D, Liu B, Wang J, Ying L. Accelerating SENSE using compressed sensing. Magnetic Resonance in Medicine. 2009;62(6): 1574-84. 12 Liu J. Dynamic cardiac MRI reconstruction with weighted redundant Haar wavelets. Magn Reson Med. 2012;Proc. ISMRM 2012,abstract. 13 Bieri O, Markl M, Scheffler K. Analysis and compensation of eddy currents in balanced SSFP. Magn Reson Med. 2005;54:129-37. 14 Muzzarelli S, Monney P, O’Brien K, Faletra F, Moccetti T, Vogt P, Schwitter J. Quantifi-cation of aortic valve regurgitation by phase-contrast magnetic resonance in patients with bicuspid aortic valve: where to measure the flow? . Eur Heart J - CV Imaging. 2013:in press. 15 Papavassiliu T, Kühl HP, Schröder M, Süselbeck T, Bondarenko O, Böhm CK, Beek A, Hofman MMB, van Rossum AC. Effect of Endocardial Trabeculae on Left Ventricular Measurements and Measurement Reproducibility at Cardio-vascular MR Imaging1. Radiology. 2005 July 1, 2005;236(1):57-64. Contact Professor Juerg Schwitter Médecin Chef Cardiologie Directeur du Centre de la RM Cardiaque du CHUV Centre Hospitalier Universitaire Vaudois – CHUV Rue du Bugnon 46 1011 Lausanne Suisse Phone: +41 21 314 0012 jurg.schwitter@chuv.ch www.cardiologie.chuv.ch Dr. G. Vincenti (cardiologist) and Dr. N. Barras (cardiologist in training, rotation), PD. Dr. S. Muzzarellli (affili-ated cardiologist), Prof. C. Beigelman and Dr. X. Boulanger (radiologists, staff members), Dr. G.L. Fetz (radiol-ogist in training, rotation), C. Gonza-les, PhD (19F-fluorine project leader), H. Yoshihara, PhD (13C-carbon project leader), V. Klinke (medical student, doctoral thesis), C. Bongard (medical student, master thesis), P. Chevre (chief CMR technician), and F. Recor-don and N. Lauriers (research nurses). Acknowledgements The authors would like to thank all the members of the team of MR tech-nologists at the CHUV for their highly valuable participation, helpfulness and support during the daily clinical CMR examinations and with the research protocols. Finally, a very important acknowledgment goes to Dr. Michael Zenge, Ms. Michaela Schmidt, and the whole Siemens MR Cardio team of Edgar Müller in Erlangen. 3 McMurray JJV, Adamopoulos S, Anker SD, Auricchio A, Böhm M, Dickstein K, Falk V, Filippatos G, Fonseca C, Sanchez MAG, Jaarsma T, Køber L, Lip GYH, Maggioni AP, Parkhomenko A, Pieske BM, Popescu BA, Rønnevik PK, Rutten FH, Schwitter J, Seferovic P, Stepinska J, Trindade PT, Voors AA, Zannad F, Zeiher A. ESC Guide-lines for the diagnosis and treatment of acute and chronic heart failure 2012. European Heart Journal. 2012 May 19, 2012(33):1787–847. 4 Zannad F, McMurray JJV, Krum H, van Veldhuisen DJ, Swedberg K, Shi H, Vincent J, Pocock SJ, Pitt B. Eplerenone in Patients with Systolic Heart Failure and Mild Symptoms. New England Journal of Medicine. 2011;364(1):11-21. 5 Gharib MI, Burnett AK. Chemotherapy-induced cardiotoxicity: current practice and prospects of prophylaxis. European Journal of Heart Failure. 2002 June 1, 2002;4(3):235-42. 6 Bardy GH, Lee KL, Mark DB, Poole JE, Packer DL, Boineau R, Domanski M, Troutman C, Anderson J, Johnson G, McNulty SE, Clapp-Channing N, Davidson- Ray LD, Fraulo ES, Fishbein DP, Luceri RM, Ip JH. Amiodarone or an Implantable Cardioverter–Defibrillator for Congestive Heart Failure. New England Journal of Medicine. 2005;352(3):225-37. 7 Schwitter J. CMR-Update. 2. Edition ed. Lausanne, Switzerland. www.herz-mri.ch. 8 Klinke V, Muzzarelli S, Lauriers N, Locca D, Vincenti G, Monney P, Lu C, Nothnagel D, Pilz G, Lombardi M, van Rossum A, Wagner A, Bruder O, Mahrholdt H, Schwitter J. Quality assessment of cardiovascular magnetic resonance in the setting of the European CMR registry: description and validation of standardized criteria. Journal of Cardiovascular Magnetic Resonance. 2013;15(1):55. 9 Bruder O, Wagner A, Lombardi M, Schwitter J, van Rossum A, Pilz G, Nothnagel D, Steen H, Petersen S, Nagel E, Prasad S, Schumm J, Greulich S, Cagnolo A, Monney P, Deluigi C, Dill T, Frank H, Sabin G, Schneider S, Mahrholdt H. European Cardiovascular Magnetic Resonance (EuroCMR) registry-multi national results from 57 centers in 15 countries. J Cardiovasc Magn Reson. 2013;15:1-9. 10 Lustig M, Donoho D, Pauly JM. Sparse MRI: The application of compressed sensing for rapid MR imaging. Magnetic Resonance in Medicine. 2007;58(6):1182-95. Accelerated Segmented Cine TrueFISP of the Heart on a 1.5T MAGNETOM Aera Using k-t-sparse SENSE Maria Carr1; Bruce Spottiswoode2; Bradley Allen1; Michaela Schmidt2; Mariappan Nadar4; Qiu Wang4; Jeremy Collins1; James Carr1; Michael Zenge2 1 Northwestern University, Feinberg School of Medicine, Chicago, IL, USA 2 Siemens Healthcare 3 Siemens Corporate Technology, Princeton, United States Introduction Cine MRI of the heart is widely regarded as the gold standard for assessment of left ventricular volume and myocardial mass and is increas-ingly utilized for assessment of car-diac anatomy and pathology as part of clinical routine. Conventional cine imaging approaches typically require 1 slice per breath-hold, resulting in lengthy protocols for complete cardiac coverage. Parallel imaging allows some shortening of the acquisition time, such that 2–3 slices can be acquired in a single breath-hold. In cardiac cine imaging artifacts become more prevalent with increasing accel-eration factor. This will negatively impact the diagnostic utility of the images and may reduce accuracy of quantitative measurements. However, regularized iterative reconstruction techniques can be used to consider-ably improve the images obtained from highly undersampled data. In this work, L1-regularized iterative SENSE as proposed in [1] was applied to reconstruct under-sampled k-space data. This technique* takes advan-tage of the de-noising characteristics of Wavelet regularization and prom-ises to very effectively suppress sub-sampling artifacts. This may allow for high acceleration factors to be used, while diagnostic image quality is preserved. The purpose of this study was to compare segmented cine TrueFISP images from a group of volunteers and patients using three acceleration and reconstruction approaches: iPAT factor 2 with conventional recon-struction; T-PAT factor 4 with conven- tional reconstruction; and T-PAT factor 4 with iterative k-t-sparse SENSE reconstruction. Technique Cardiac MRI seems to be particularly well suited to benefit from a group of novel image reconstruction methods known as compressed sensing [2] which promise to significantly speed up data acquisition. Compressed sensing methods were introduced to MR imaging [3, 4] just a few years ago and have since been successfully combined with parallel imaging [5, 6]. Such methods try to utilize the * Work in progress: The product is still under development and not commercially available yet. Its future availability cannot be ensured. Table 1: MRI conventional and iterative imaging parameters Parameters Conventional iPAT 2 Conventional T-PAT 4 Iterative T-PAT 4 Iterative recon No No Yes Parallel imaging iPAT2 (GRAPPA) TPAT4 TPAT4 TR/TE (ms) 3.2 / 1.6 3.2 / 1.6 3.2 / 1.6 Flip angle (degrees) 70 70 70 Pixel size (mm2) 1.9 × 1.9 1.9 × 1.9 1.9 × 1.9 Slice thickness (mm) 8 8 8 Temp. res. (msec) 38 38 38 Acq. time (sec) 7 3.2 3.2 Clinical Cardiovascular Imaging 26 MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world Cardiovascular Imaging Technology Reprinted from MAGNETOM Flash 5/2013 Reprinted from MAGNETOM Flash 5/2013 MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world 27
- 15. As outlined by Liu et al. in [1], the image reconstruction can be formu-lated as an unconstrained optimization problem. In the current implementa-tion, this optimization is solved using a Nesterov-type algorithm [7]. The L1-regularization with a redundant Haar transform is efficiently solved using a Dykstra-type algorithm [8]. This allowed a smooth integration into the current MAGNETOM platform and, therefore, facilitates a broad clinical evaluation. Materials and methods Nine healthy human volunteers (57.4 male/56.7 female) and 20 patients (54.4 male/40.0 female) with suspected cardiac disease were scanned on a 1.5T MAGNETOM Aera system under an approved institutional review board protocol. All nine volun-teers and 16 patients were imaged using segmented cine TrueFISP sequences with conventional GRAPPA factor 2 acceleration (conventional iPAT 2) T-PAT factor 4 acceleration (conventional T-PAT 4), and T-PAT factor 4 acceleration with iterative k-t-sparse SENSE reconstruction (iterative T-PAT 4). The remaining 4 patients were scanned using only conventional iPAT 2 and iterative T-PAT 4 techniques. Note that the iterative technique is fully integrated into the standard reconstruction environment. The imaging parameters for each imaging sequence are provided in Table 1. All three sequences were run in 3 chamber and 4 chamber views, as well as a stack of short axis slices. Quantitative analysis was performed on all volunteer data sets at a syngo MultiModality Workplace (Leonardo) using Argus post-processing software (Siemens Healthcare, Erlangen, Germany) by an experienced cardio-vascular MRI technician. Ejection frac-tion, end-diastolic volume, end-systolic volume, stroke volume, cardiac out-put, and myocardial mass were calcu-lated. In all volunteers and patients, 5 4 3 2 1 blinded qualitative scoring was per-formed by a radiologist using a 5 point Likert scale to assess overall image quality (1 – non diagnostic; 2 – poor; 3 – fair; 4 – good; 5 – excellent). Images were also scored for artifact and noise (1 – severe; 2 – moderate; 3 – mild; 4 – trace; 5 – none). All continuous variables were com-pared between groups using an unpaired t-test, while ordinal qualita-tive variables were compared using a Wilcoxon signed-rank test. Results All images were acquired successfully and image quality was of diagnostic quality in all cases. The average scan time per slice for conventional iPAT 2, conventional T-PAT 4 and iterative T-PAT 4 were for patients 7.7 ± 1.5 sec, 5.6 ± 1.5 sec and 2.9 ± 1.5 sec and for the volunteers 9.8 ± 1.5 sec, 3.2 ± 1.5 sec and 3.0 ± 1.5 sec, respectively. The results in scan time are illustrated in Figure 1. In both patients and volun-teers, conventional iPAT 2 were signifi-cantly longer than both conventional T-PAT 4 and iterative T-PAT 4 techniques (p < 0.001 for each group). The results for ejection fraction (EF) for all three imaging techniques are provided in Figure 2. The average EF for conventional T-PAT 4 was slightly lower than that measured for con-ventional iPAT 2 and iterative T-PAT, but the group size is relatively small (9 subjects) and this difference was not significant (p = 0.34 and p = 0.22 respectively).There was no statisti-cally significant difference in ejection fraction between the conventional iPAT 2 and the iterative T-PAT 4 sequences (p = 0.48). The results for image quality, noise and artifact are provided in Figure 3. The iterative T-PAT 4 images had com-parable image quality, noise and arti-fact scores compared to the conven-tional iPAT 2 images. The conventional T-PAT 4 images had lower image qual-ity, more artifacts and higher noise compared to the other techniques. Figures 4 and 5 show an example of 4-chamber and mid-short axis images from all three techniques in a patient with basal septal hypertrophy. In both series’, the conventional iPAT 2 and iterative T-PAT 4 images are compara-ble in quality, while the conventional T-PAT 4 image is visibly noisier. Cardiovascular Imaging Technology Discussion This study compares a novel acceler-ated segmented cine TrueFISP tech-nique to conventional iPAT 2 cine TrueFISP and T-PAT 4 cine TrueFISP in a cohort of normal subjects and patients. The iterative reconstruction technique provided comparable mea-surements of ejection fraction to the clinical gold standard (conventional iPAT 2). The accelerated segmented cine TrueFISP with T-PAT 4, which was used as comparison technique, produced slightly lower EF values compared to the other techniques, although this was not found to be statistically significant. The iterative reconstruction produced comparable image quality, noise and artifact scores to the conventional reconstruc-tion using iPAT 2. The conventional T-PAT 4 technique had lower image quality and higher noise scores com-pared to the other two techniques. The iterative T-PAT 4 segmented cine technique allows for greater than 50% reduction in acquisition time for comparable image quality and spatial resolution as the clinically used iPAT 2 cine TrueFISP technique. This itera-tive technique could be extended to permit complete heart coverage in a single breath-hold thus greatly sim-plifying and shortening routine clini-cal cardiac MRI protocols, which has been one of the biggest obstacles to wide acceptance of cardiac MRI. With a shorter cine acquisition, additional advanced imaging techniques, such as perfusion and flow, can be more readily added to patient scans within a reasonable protocol length. Technology Cardiovascular Imaging 12 10 8 6 4 Single slice scan time in patients and volunteers. There was a statistically significant reduction in scan time compared to the standard iPAT2 for both TPAT4 acceleration and iterative reconstruction TPAT4 acceleration. 1 Qualitative scores in patients and volunteers. Image quality was highest and noise and artifact were lowest with iterative T-PAT 4 and conventional iPAT 2 compared to conventional T-PAT 4. 3 full potential of image compression during the acquisition of raw input data. In the case of highly subsam-pled input data, a non-linear iterative optimization avoids sub-sampling artifacts during the process of image reconstruction. The resulting images represent the best solution consis-tent with the input data, which have a sparse representation in a specific transform domain. In the most favor-able case, residual artifacts are not visibly perceptible or are diagnosti-cally irrelevant. 0 Conventional iPAT 2 Scan Time (sec) Conventional T-PAT 4 Iterative T-PAT 4 2 Standard iPAT 2 T-PAT 4 Acceleration Iterative Reconstruction T-PAT 4 Accel. 0 Quality Noise Artifact 1 3 65,00 60,00 55,00 50,00 45,00 40,00 Ejection fraction in volunteers. Quantitatively measured ejection fractions were comparable across all three techniques. 2 Conventional iPAT 2 Ejection Fraction (%) Conventional T-PAT 4 Iterative T-PAT 4 2 28 MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world Reprinted from MAGNETOM Flash 5/2013 Reprinted from MAGNETOM Flash 5/2013 MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world 29
- 16. Technology Cardiovascular Imaging Cardiovascular Imaging Technology There are currently some limitations to the technique. Firstly, the use of SENSE implies that aliasing artifacts can occur if the field-of-view is smaller than the subject, which is sometimes difficult to avoid in the short axis orientation. But a solution to this is promised to be part of a future release of the current proto-type. Secondly, the image reconstruc-tion times of the current implemen-tation seems to be prohibitive for routine clinical use. However, we anticipate future algorithmic 6A 6B 6 Real-time cine TrueFISP T-PAT 6 images reconstructed using (6A) conventional, and (6B) iterative techniques. Contact Maria Carr, RT (CT)(MR) CV Research Technologist Department of Radiology Northwestern University Feinberg School of Medicine 737 N. Michigan Ave. Suite 1600 Chicago, IL 60611 USA Phone: +1 312-926-5292 m-carr@northwestern.edu References 1 Liu J, Rapin J, Chang TC, Lefebvre A, Zenge M, Mueller E, Nadar MS. Dynamic cardiac MRI reconstruction with weighted redundant Haar wavelets. In Proceedings of the 20th Annual Meeting of ISMRM, Melbourne, Australia, 2002. p 4249. 2 Candes EJ, Wakin MB. An Introduction to compressive sampling. IEEE Signal Processing Magazine 2008. 25(2):21-30. doi: 10.1109/MSP.2007.914731. improvements with increased compu-tational power to reduce the recon-struction time to clinically acceptable values. Of course, iterative reconstruction techniques are not just limited to cine imaging of the heart. Future work may see this technique applied to time intense techniques such as 4D flow phase contrast MRI and 3D coronary MR angiography, making them more clinically applicable. Furthermore, higher acceleration rates might be achieved by using an incoherent sampling pattern [9]. With sufficiently high acceleration, the technique can also be used effectively for real time cine cardiac imaging in patients with breath-holding difficul-ties or arrhythmia. Figure 6 shows that real-time acquisition with T-PAT 6 and k-t iterative reconstruction still results in excellent image quality. In conclusion, cine TrueFISP of the heart with inline k-t-sparse iterative reconstruction is a promising tech-nique for obtaining high quality cine images at a fraction of the scan time compared to conventional techniques. Acknowledgement The authors would like to thank Judy Wood, Manger of the MRI Department at Northwestern Memorial Hospital, for her continued support and collabo-ration with our ongoing research through the years. Secondly, we would like to thank the magnificent Cardio-vascular Technologist’s Cheryl Jarvis, Tinu John, Paul Magarity, Scott Luster for their patience and dedication to research. Finally, the Resource Coordi-nators that help us make this possible Irene Lekkas, Melissa Niemczura and Paulino San Pedro. 3 Block KT, Uecker M, Frahm J. Unders-ampled Radial MRI with Multiple Coils. Iterative Image Reconstruction Using a Total Variation Constraint. Magn Reson Med 2007. 57(6):1086-98. 4 Lustig M, Donoho D, Pauly JM. Sparse MRI: The application of compressed sensing for rapid MR imaging. Magn Reson Med 2007. 58(6):1182-95. 5 Liang D, Liu B, Wang J, Ying L. Acceler-ating SENSE using compressed sensing. Magn Reson Med 2009. 62(6):154-84. doi: 10.1002/mrm.22161. 6 Lustig M, Pauly, JM. SPIRiT: Iterative self- consistent parallel imaging reconstruction from arbitrary k-space. Magn Reson Med 2010. 64(2):457-71. doi: 10.1002/mrm.22428. 7 Beck A, Teboulle M. A fast iterative shrinkage-thresholding algorithm for linear inverse problems. SIAM J Imaging Sciences 2009. 2(1): 183-202. 8 Dykstra RL. An algorithm for restricted least squares regression. J Amer Stat Assoc 1983 78(384):837-842. 9 Schmidt M, Ekinci O, Liu J, Lefebvre A, Nadar MS, Mueller E, Zenge MO. Novel highly accelerated real-time CINE-MRI featuring compressed sensing with k-t regularization in comparison to TSENSE segmented and real-time Cine imaging. J Cardiovasc Magn Reson 2013. 15(Suppl 1):P36. 4A 4B 4C Four chamber cine TrueFISP from a normal volunteer. (4A) Conventional iPAT 2, acquisition time 8 s. (4B) Conventional T-PAT 4, acquisition time 3 seconds. (4C) Iterative T-PAT 4, acquisition time 3 seconds. 4 5A 5B 5C End-systolic short axis cine TrueFISP images from a patient with a history of myocardial infarction. A metal artifact from a previous sternotomy is noted in the sternum. There is wall thinning in the inferolateral wall with akinesia on cine views, consistent with an old infarct in the circumflex territory. (5A) Conventional iPAT 2, (5B) conventional T-PAT 4, (5C) iterative T-PAT 4. 5 30 MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world Reprinted from MAGNETOM Flash 5/2013 Reprinted from MAGNETOM Flash 5/2013 MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world 31
- 17. Combined 18F-FDG PET and MRI Evaluation of a case of Hypertrophic Cardiomyopathy Using Simultaneous MR-PET Ihn-ho Cho, M.D.; Eun-jung Kong, M.D. Department of Nuclear Medicine, Yeungnam University Hospital, Daegu, South Korea Introduction Hypertrophic cardiomyopathy (HCM) is a common condition causing left ventricular outflow obstruction, as well as cardiac arrhythmias. Cardiac MRI is a key modality for evaluation of HCM. Apart from estimating left ventricular (LV) wall thickness, LV function and aortic flow, MRI is capa-ble of estimating the late gadolinium enhancement in affected myocardium, which has been shown to have a direct correlation with incidence and Patient history A 25-year-old man presented to the cardiology department with inciden-tal ECG abnormality after fractures to his left 2nd and 4th fingers. Although he had not consulted a doctor, he had been suffering from mild dyspnea with chest discomfort at rest and exacerbation at exercise since May 2012. Echocardiography revealed non-obstructive hypertrophic cardio-myopathy (Maron III) with trivial MR. The patient was referred for a simul-taneous MR-PET study for 18F-FDG PET and cardiac MRI with Gadolinium (Gd) contrast for evaluation of the morphological and metabolic status of the hypertrophic myocardium. The patient was injected with 10 mCi 18F- FDG following glucose loading. Simultaneous MR-PET study per-formed on a Biograph mMR was started one hour following tracer injection. Following standard Dixon sequence acquisition for attenuation correction, the comprehensive car-diac MRI sequences were acquired including MR perfusion after Gd con-trast infusion, as well as post contrast late Gd enhancement studies. Static 18F-FDG PET was acquired simultane-ously during the MRI acquisition. Cardiovascular Imaging Clinical 2A 2 Discussion The late Gd enhancement within the hypertrophic septum along with the non-uniform glucose metabolism demonstrated by the patchy 18F-FDG uptake within the hypertrophic septum exactly corresponding to the area of Gd enhancement reflect myocardial fibrosis within the asymmetric septal hypertrophy. Myocardial fibrosis and the presence of late Gd enhancement on MRI has been shown to be associ-ated with increased risk of cardiac arrhythmia [1] as evident from the symptoms of this patient. severity of arrhythmias in HCM [1]. In patients with HCM, late gadolinium enhancement (LGE) on CE-MRI is pre-sumed to represent intramyocardial fibrosis. PET myocardial perfusion studies have shown slight impairment of myocardial blood flow with phar-macological stress in hypertrophic myocardium in HCM, presumably related to microvascular disease [2]. 18F-FDG PET has been sporadically studied in HCM, mostly for evalua-tion of the metabolic status of the hypertrophic myocardial segment, espe-cially after interventions such as trans-coronary ablation of septal hypertro-phy (TASH) [3] or to demonstrate partial myocardial fibrosis [4]. This clinical example illustrates the value of integrated simultaneous 18F-FDG PET and MRI acquisition performed on the Biograph mMR system. 1A 1B Short-axis views of end diastole and end systole at 3 different sections in the left ventricle obtained from gated TrueFISP cine MRI acquisitions performed on Biograph mMR. Note the thick hypertrophic septum (white arrow), which demonstrates the degree of asymmetric septal hypertrophy. 1 1D 1F 1C 1E 1G 1 1 End Diastole End Systole 2 3 2 3 Simultaneous MR-PET acquisition provides combined acquisition of both modalities, thereby ensuring accurate fusion between morphologi-cal and functional images due to simultaneous PET acquisition for every MR sequence. The exact coregistra-tion of the patchy 18F-FDG uptake in the area of Gd enhancement within the hypertrophic upper septum reflects the advantage of simultane-ous acquisition. End diastolic and end systolic views of 2-chamber and 4-chamber views obtained from gated cine TrueFISP acqui-sitions showing thickness of the asymmetric septal hyper-trophy (white arrow). 2C 2B 2D End Diastole 4-chamber view 2-chamber view End Systole 3 3 Static 18F-FDG PET images in short-axis, horizontal long-axis and vertical long-axis views demonstrating normal uptake in the LV myocardium except the non-uniform uptake pattern in the hypertro-phied septum (white arrows). LV cavity size appears normal. MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world 33 Clinical Cardiovascular Imaging 32 MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world Reprinted from MAGNETOM Flash 5/2013 Reprinted from MAGNETOM Flash 5/2013
- 18. Clinical Cardiovascular Imaging Further Reading 4 5 Contact Ihn-ho Cho, M.D. Department of Nuclear Medicine Yeungnam University College of Medicine Daegu Hyunchungro 170 South Korea nuclear126@ynu.ac.kr 4D T2 HASTE T2 STIR T1 FAT SAT 4B 4E References 1 Rubinstein et al. Characteristics and Clinical Significance of Late Gadolinium Enhancement by Contrast-Enhanced Magnetic Resonance Imaging in Patients With Hypertrophic Cardiomyopathy. Circ Heart Fail. 2010;3:51-58. 2 Bravo et al. PET/CT Assessment of Symptomatic Individuals with Obstructive and Nonobstructive Hypertrophic Cardio-myopathy. J Nucl Med 2012; 53:407–414. Transverse, short-axis and vertical long-axis MR and fused MR-PET images show hypertrophied septum (white arrows) and normal thickness of rest of left ventricular myocardium with corresponding normal 18F-FDG uptake. The T2-weighted STIR (fat suppression) image shows slight hyperintensity in the middle of the hypertrophied septum which shows corresponding non-uniformity in 18F-FDG uptake. Post-contrast MR short-axis images demonstrate late Gd enhancement within the hypertrophied septum (white arrow), which shows corresponding non-uniform patchy uptake of 18F-FDG. 4A 5A 5B 4C 4F 4 Funabashi N et al. Partial myocardial fibrosis in hypertrophic cardiomyopathy demonstrated by 18F-fluoro-deoxy-glucose positron emission tomography and multislice computed tomography. Int J Cardiol. 2006 Feb 15;107(2):284-6. 3 Kuhn et al. Changes in the left ventricular outflow tract after transcoronary ablation of septal hypertrophy (TASH) for hypertrophic obstructive cardiomy-opathy as assessed by transoesophageal echocardiography and by measuring myocardial glucose utilization and. perfusion. European Heart Journal (1999) 20, 1808–1817. 34 MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world Cardiac MRI at 3T: An Indian Experience of 80 Cases Cardiac MRI at 3T: An Indian Experience of 80 Cases of Cardiac MRI with Review of Literature Kalashree A. Bidarkar DNB; Nikhil Kamat, M.D., DMRD, DNB; M. L. Rokade, M.D., DNB; Nitin Burkule, M.D., DM; Shubra Gupta Departments of Radiology and Cardiology, Jupiter Hospital, Thane, Maharashtra, India Diagram 1 [7]: A schematic representation of three zones of affection in case of an MI: Clinical Cardiology Cardiology Clinical 3 3A, B, 4C, 2C views reveal moderate dilated LA and LV with thinning of LV anterior wall, interventricular regions and the apex. Aneurysmal dilatation of the thinned apex is seen (thin yellow arrows). Figure 4 demonstrates CMR findings in acute myocardial infarction, seen as edema on T2-weighted images and perfusion defect (microvascular obstruction) on the post-contrast PSIR images. B) Pericardium MRI is particularly suitable for eval-uation of pericardial inflammation, evaluation of small or loculated pericardial effusions, functional abnormalities caused by pericardial constriction, and for characteriza-tion of pericardial masses [19]. 1A Clinical Cardiology Cardiology Clinical 7 The diagnosis of constrictive peri-carditis is greatly aided by excellent depiction of pericardium at MR imaging. Normal pericardium is less than 3 mm thick. Pericardial thick-ness of 4 mm or more indicates abnormal thickening, and when accompanied by clinical signs of heart failure is highly suggestive 2A of constrictive pericarditis [10]. Peri-cardial thickening may be limited to the right side of the heart or even a smaller area such as the right atrio-ventricular groove. In chronic constrictive pericarditis there is typically bi-atrial enlarge-ment. 35-year-old male patient on treatment for pulmonary Koch’s disease, presented with dyspnoea. (5A, B) Horizontal long axis black and white blood images reveal thickened pericardium (6 mm). (5C, D) Post-contrast images acquired 15 minutes post Gd administration reveal diffuse pericardial enhancement consistent with the diagnosis of constrictive pericarditis. 5 1B Clinical Cardiology Cardiology Clinical Also, the central cardiovascu-lar 2B structures show a characteristic morphology with the right ventricle showing a narrow tubular configu-ration [10]. Cine images are useful to judge the pathophysiologic consequence of pericardial thickening and the ‘Diastolic Septal bounce’ [7]. Diastolic septal bounce is a hemo-dynamic hallmark of ventricular constriction seen due to increased interventricular dependence and demonstrated as abnormal ventric-ular septal 6A 6B 32-year-old male patient with a history of sudden atrial fibrillation was evaluated by CMR. (9A, B) SSFP sequential 3-chamber SSFP cine MR images in the diastolic and mid-systolic phases respectively reveal LV hyper-trophy (7C, D) PSIR images acquired 15 minutes post Gd administration reveal patchy transmural LGE in the thickened IV septum and RV insertion sites, suggestive of scarred tissue (solid white arrows). Clinical Cardiology Cardiology Clinical 8 21-year-old male patient with complaints of progressive dyspnoea since childhood was referred for CMR. (12A, B) SSFP 4- and 2-chamber views reveal moderate cardiomegaly. Clinical Cardiology Cardiology Clinical 15 46-year-old asymptomatic male patient with a family history of sudden cardiac deaths came to our institution for CMR evaluation. (15A, B) SSFP short axis images reveal severe non-compaction of the apex, mid lateral and mid anterior walls with a ratio of NC/C being 2.7 suggestive of non-compaction CMP. Left atrial dilatation was also observed. Figures 15, 16 demonstrate the imag-ing characteristics in non-compaction CMP. Cardiac masses CMR is widely recognised as the imag-ing modality of choice in evaluation of cardiac masses. Invasion in to adjacent structures, precise compartmental localisation can be easily accomplished narrowing the differential diagnosis [9]. 1) Thrombus: a common differential diagnosis for cardiac tumors is intracardiac thrombus. Thrombi may appear isointense or slightly hyperintense relative to the myocardium on black blood pre-pared MRI enables differentia-tion between thrombus and surrounding myocardium as throm-bus being avascular is character-ized by lack of contrast uptake. Rarely, large chronic thrombi may show peripheral enhancement and be diagnostically challenging [17]. Figure 17 shows a case of a patient suspected to have a LV clot (on echocardiography), confirmed on CMR. 2) Cardiac myxomas: These account Their contours are round or oval, sometimes lobulated with a smooth surface and a narrow pedicle. They have a gelatinous structure and may be relatively high in signal on SSFP and static images. They typi-cally demonstrate heterogeneous enhancement on delayed-enhance-ment images [9] (Fig. 18). We encountered one patient referred for a CMR for assessment of a mass attached to the inter-ventricular septum (as seen on echocardiography). Although the location was uncommon, the mass showed morphologic and enhance-ment Table 1: MR sequencing Anatomy HASTE 2D Function Cine SSFP (2CV,4CV,SA) Morphology T1-weighted (2CV,4CV,SA) STIR dark blood (2CV,4CV,SA) Fluid content T2-weighted (2CV,4CV,SA) Gadolinium kinetics TI scout baseline Delayed enhancement IR turbo TrueFISP 2D Abbreviations: 2D, 2 dimensional ; CV, chamber view; IR, inversion recovery; SA, short axis; TI, inversion time; STIR, Short TI Inversion Recovery; TSE, turbo spin echo Table 2: Special considerations Acute MI T2-weighted or STIR dark blood Cardiac mass or thrombus TSE dark blood T1, TSE dark blood T2 fat sat Clinical Cardiology Cardiology Clinical 18 for 20–25% of cardiac tumors. The most common locations are in the left atrium (60–75%), right atrium (20–28%), but rarely in both the atria and ventricles [17]. characteristics of a myxoma and was diagnosed as such. 17 LV clots in a 65-year-old male patient with dyspnoea. (17A, B) PSIR images acquired 15 minutes post Gd administration reveal transmural LGE in the apex and the anteroseptal wall suggestive of non-viable myocardium in the LAD. A layered non-enhancing clot is seen at the apex adjacent to the akinetic apical myocardium (thin yellow arrows). 20 Figure 21A: Shows ventricular septal defect (arrow). 22 14A 14B 14C HASTE images [21] .Contrast-enhanced 19 (15C, D) PSIR images acquired 15 minutes after Gd administration showed moderate patchy LGE involving the anterior wall and interventricular septum, predominantly at the RV insertion sites (asterisk in C). 16 Another case of non-compaction CMP in a 28-year-old post-partum female with mild dyspnoea on exertion. (16A, B) SSFP 4-chamber view and short axis images reveal moderate cardio-megaly with non-compaction seen along the lateral, inferior and posterior walls and the apex (white solid arrows). 18 55-year-old male patient with a history of recurrent TIAs for CMR evaluation. (18A, B) SSFP 4-chamber and short axis views reveal a nodular soft tissue mass adherent to the IV septum (solid white arrows). 13 13 MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world 14 MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world 35 Cardiac MRI is the main investigation modality for a wide range of clinical applications and has emerged as a virtual ‘one-stop-shop’ for imaging conditions such as Cardiomyopathies. CMR has added uniquely to the methods for non-invasive assessment of myocardial viability by a combina-tion of cine imaging and delayed hyper-enhancement. CMR provides excellent depiction of pericardium in conditions such as pericarditis, Read the comprehensive article www.siemens.com/ magnetom-world pericardial effusions, and masses. It provides optimal assessment of the location, functional characteristics, and soft tissue features of cardiac tumors, allowing accurate differen-tiation of benign and malignant lesions. MRI is ideally suited to serve as the primary imaging modality in patients with congenital heart disease due its non-invasive and biologically harm-less nature, and its ability to provide accurate anatomical and functional information. Several investigators have confirmed the SNR advantages of CMR at 3T. These indicate an overall quan-titative improvement in SNR and CNR, thus improving imaging capabilities. Dr. Bidarkar and colleagues (Depart-ments of Radiology and Cardiology, Jupiter Hospital, Thane, Maharashtra, India) illustrate 80 cases of cardiac MRI imaged between January 2012 and August 2013 on a 3T MAGNETOM Verio. Contrast-enhanced study of the LV myxoma. (18E, F) PSIR images acquired 5 minutes and 15 minutes post Gd adminis-tration reveal minimal to no enhancement in the 5 min scan and intense homog-enous enhancement in the delayed scan (solid white arrows). Congenital heart diseases Congenital heart disease is a com-mon clinical entity and occurs in 0.8% of newborns [23]. Major advances in hardware design, new pulse sequences, and faster image reconstruction techniques allow rapid high resolution imaging of complex cardiovascular anatomy and physiology [24]. In our study, we imaged one 9-year-old male patient with complaints of progressive dyspnoea. Since contact of patients with CHDs referred for cardiac MRI exam is limited, we frag-mented a single case of complicated CHD to demonstrate various cardiac anomalies. The CMR study demonstrated the following cardiac anomalies: • Ventricular septal defect: A com-mon congenital heart disease clas-sified into membranous, muscular, endocardial cushion defects, and conal [23] (Fig. 21A). • Atroial septal defect: The main types of ASD are secundum (middle of atrial septum) as seen in figure 21B, sinus venosus (at junction of SVC and right atrium superiorly), and primum (near the AV valves) [23]. • Patent ductus arteriosus: PDA is the persistence of the 6th aortic arch and accounts for 10% of congenital heart disease. MRI demonstrates a persistent connection between the origin of left pulmonary artery to the descending aorta just beyond origin of the left subclavian artery [23] as seen in figure 22. • Transposition of great arteries: The most common congenital heart lesion found in neonates, found in 5–7% of congenital cardiac malfor-mations. Congenitally-corrected transposition refers atrioventricular discordance, ventricular inversion transposition, and inversion of great arteries [25] (Fig. 19). Also observed in the same patient was situs inversus as shown in figure 20. Limitations A few technical limitations we encoun-tered during our study on a 3T MRI were: • Inability to achieve optimal myocar-dial nulling: Optimal TI scout was not obtained in three of our patients despite repeated attempts • Exaggerated flow artifacts: Flow arti-facts seemed to be more pronounced in areas of turbulent blood flow. These technical issues have been for-warded to the Siemens application team and are currently under review. The team has in the past overcome many technical challenges of cardiac Coronal T2-weighted image shows liver situated on left side of the abdomen – situs inversus. (21B) Shows atrial septal defect, secundum type (arrow). 21 (22A, B) Demonstrate persistent ductus arteriosus (PDA) connecting aorta to pulmonary artery. MRI on 3T due to high gradient factors in comparison with 1.5T, and opti-mized the protocol of cardiac MRI on 3T. With this experience, the team appears confident of being able to pro-vide a solution to these limitations in the near future. Conclusion Cardiac MRI forms a mainstay investi-gation modality for a wide range of clinical applications and has emerged as a virtual ‘one-stop’ for imaging conditions like Cardiomyopathies [11]. CMR has added uniquely to the meth-ods for non-invasive assessment of myocardial viability by a combination of cine imaging and delayed hyper-enhancement (LGE). 18E 18F Figure 19A: Shows right sided aortic arch (asterisk). (19B) Shows that the aorta arises from the morpho-logical right ventricle (curved arrow). 19A 19B (22C) Demonstrates multiple aortopulmonary collaterals (MAPCAs) (red arrows). (22D) Shows the atretic pulmonary trunks and main branch pulmonary arteries measuring 4 mm in diameter (yellow asterisk). 20 21A 21B 22A 22B 22C 22D 15 MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world 16 15A 15B 15C 15D 16A 16B 16C 16D (16C, D) PSIR images acquired 15 minutes post Gd administration reveal mild subendocardial LGE in the septal region, anterior and posterior walls, not conforming to any vascular territory (thin yellow arrows). 17A 17B 18A 18B 18C 18D (18C, D) T1-weighted short axis and STIR 4-chamber views respectively demonstrate the mass which appears isointense to the myocardium on T1w and hyperintense on STIR images (myxoid content) suggestive of LV myxoma (solid red arrows). NC/C ratio = 2.7 12 Example of an advanced case of idiopathic dilated cardiomyopathy in a 34-year-old female patient with dyspnoea and intermittent chest pain. (13A, B) SSFP 4- and 2-chamber views respectively, show dilatation of all the cardiac chambers. myocytes. The abnormalities seen in primary dilated cardiomyopathies are fairly similar to those seen as an end result of CAD (ischemic cardiomyopa-thy) [7]. LGE can be seen in both entities. However, ischemic injury pro-gresses as a wavefront from the subendocardium to epicardium and shows a territorial distribution (Fig. 11). Hyper-enhancement patterns that spare the subendocardium and are limited to middle or epicardial portions of the LV, are clearly in a non-CAD dis-tribution [9] (Fig. 12). Restrictive cardiomyopathy Restrictive CMP is characterised by reduced ventricular filling and diastolic volume, leading to atrial dilatation and venous stasis, with preserved systolic function. Restrictive CMP may be idio-pathic, secondary to infiltrative and storage disorders (such as amyloidosis and sarcoidosis) or associated with myocardial disorders such as hypereo-sinophilic syndrome. Cardiac MRI is a fundamental diagnos-tic tool because it helps in differentiat-ing between restrictive CMP and con-strictive pericarditis which have different therapeutic approaches. Although reduced ventricular filling and diastolic volumes may be a fea-ture of both, pericardial thickening > 4 mm is typical of pericarditis [12] (Fig. 5). Cardiac MRI also helps in the differ-entiation between the above entities in cases with minimally thickened pericardium. Morphologic images in restrictive CMP may show atrial enlargement. Cine images allow assessment of altered diastolic ven-tricular filling. Cine MRI assessment of diastolic ventricular septal move-ments and real time MRI imaging of septal movements during respiration show that in restrictive CMP, septal convexity is maintained in all respira-tory phases, whereas in constrictive pericarditis, septal flattening can be seen in early inspiration [12] (Fig. 6). The issue of LGE in idiopathic restric-tive CMP has not been specifically addressed in the literature, although late enhancement patterns in specific causes of restrictive CMP have been described [12]. Figure 14 illustrates a case of Restric-tive CMP. Non-compaction cardiomyopathy Left ventricular myocardial non com-paction (LVNC) is a recently recog-nised form of primary and genetic cardiomyopathy. Also known as spongy myocardium, LVNC is charac-terised by prominent ventricular myocardial trabeculations and deep intertrabecular recesses communicat-ing with the ventricular cavity. LVNC is secondary to arrest in the normal process of myocardial compaction during fetal life. CMR can clearly display the com-pacted and non-compacted myocar-dium layers better than echocardiog-raphy [13]. In a normal ventricle, the proportion of ventricular wall formed by trabec-ulations never exceeds thickness of the compacted layer. In LVNC, the thickness of non-compact myocardium is greater than that of compacted layer which is thinned. It is suggested that a NC/C ratio > 2.3 in diastole dis-tinguishes pathological non compac-tion from pronounced trabeculae seen in other CMPs [13]. (12C, D) PSIR images acquired 15 minutes post Gd administration reveal no LGE in the myocardium to suggest fibrosis. The patient was diagnosed as idiopathic/non ischaemic dilated cardiomyopathy. (13C, D) PSIR images acquired 15 minutes post Gd administration reveal diffuse subendocardial LGE in the septal, anterior and posterior walls (thin yellow arrows). Mild pericardial effusion can be appre-ciated on the short axis view (white solid arrow). 12A 12B 10 12C 12D 13A 13B 13C 13D 13-year-old female patient with a history of progressive dyspnoea. (14A) SSFP images in the horizontal long axis view reveals significant bi-atrial dilatation (thin yellow arrows) with normal sized ventricular cavities. (14B, C) PSIR images acquired 15 minutes post Gd administration demonstrate no enhancement in the myocardium. Findings were suggestive of restrictive cardiomyopathy. 14 11 MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world 12 motion towards the left ventricle in early diastole during onset of inspiration [9]. This finding is help-ful (double headed arrow in 9B) and LA dilatation (thin yellow arrow). (9C) Systolic phase demonstrates anterior motion of the mitral leaflet causing obstruction at the LVOT (solid yellow arrow) with resultant turbulent jets in the LA and at the LVOT – systolic anterior motion (SAM). 9 Preclinical HCM. Shown are images of a 35-year-old asympto matic male patient with a family history of HCM. (10A, B) SSFP sequential 4-chamber and short axis SSFP cine MR images reveal mid biatrial dilatation (thin yellow arrows) with no significant myocardial hypertrophy (double headed blue arrows). entities. Mass-like HCM more pre-cisely parallels the homogenous signal intensity characteristics and perfusion of adjacent normal myo-cardium, while tumors show hetero-geneous signal intensity, enhance-ment, and perfusion characteristics that differ from those of remainder of the left ventricle [20]. 6) Pre-clinical HCM Screening of family members of patients with HCM is important because first-degree relatives of such patients have a 50% chance of being a gene carrier. Cardiac MRI is a useful screening tool in patients with a normal LV thickness who have symptoms of HCM or in asymptomatic HCM mutation carriers. However, dis-ease expression can be heteroge-nous and varied, even with the same mutation; hence follow-up screening needs to be considered every 2 to 5 years, particularly in young patients [20]. Figure 10 illustrates CMR finding s in a 36-year-old asymptomatic male patient with a family history of HCM. Dilated cardiomyopathy (DCM) These are a common cause of con-gestive heart failure characterized by fibrosis and decreased number of CMR of a 65-year-old male patient with a history of anterior wall MI. (11A, B) SSFP 4- and 2-chamber chamber views reveal moderately dilated left ventricle. (11B, C) PSIR images acquired 15 minutes post Gd administration reveals transmural LGE in the antero-septal wall, suggestive of non-viable myocardium in the LAD and RCA territories (thin yellow arrows). The patient was diagnosed as ischaemic dilated cardiomyopathy. 11 9A 9B 9C (10C, D) PSIR images acquired 15 minutes post Gd administration reveal LGE along the inferior and posterior walls suggestive of early fibrosis. in distinguishing between con-strictive pericarditis and restrictive cardiomyopathy [9] (Fig. 6). Figure 5 illustrates the characteristic findings of thickened pericardium and diffuse pericardial enhancement in a case of constrictive pericarditis. 10A 10B 10C 10D 11A 11B 11C 11D 9 MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world 10 (3B, C) PSIR images taken 15 minutes post Gd administration reveal transmural LGE in these (solid white arrows) areas suggestive of non-viable myocardium in the LAD territory. C) Cardiomyopathies (CMPs) Cardiomyopathies are chronic progressive diseases of the myo-cardium with often genetic / inflammation / injury as factors contributing to their development [7]. Cardiac MRI has become an important tool for the diagno-sis and follow-up of patients with cardiomyopathies. It has a unique ability to differentiate between different enhancement patterns in diseased myocardium on inversion recovery delayed Gadolinium-enhanced images, making it suit-able for evaluation of cardiomyop-athies [18]. 4 42-year-old male patient with symptoms of acute myocardial infarction. (4A, B) SSFP 4-chamber and short axis images reveal mildly thickened interventricular septum with subtle hyperintense areas suggestive of post-MI edema (solid red arrows). Hypertrophic cardiomyopathy (HCM): A genetically-acquired condition resulting from abnormal-ity in the sarcomere, it results in hypertrophy of the myocardium. MRI has proven to be an important tool in the evaluation of patients with suspected HCM since it helps readily diagnose those with phe-notypic expression of the disorder and potentially identify the subset of patients at risk of sudden car-diac deaths. MRI is also capable of detecting regions of localised hypertrophy that are missed by echocardiography. A significant percentage of patients with HCM demonstrate LGE char-acteristically involving regions of hypertrophy, junctions of interven-tricular septum and RV free wall [9]. LGE is usually patchy and mid-wall in location. LGE in HCM also has a predilection for the anterior and posterior insertion points. An exception to this is in areas of burnt-out myocardium where the left ventricular wall is thinned and enhancement is full thickness [18]. The presence of LGE denotes scar tissue, a potential nidus for fatal arrhythmias. CMR can be used to follow the patients following ventricular septal resection / percu-taneous ablation [7]. Phenotypes of HCM 1) Asymmetric HCM This is the most common morpho-logic presentation of HCM, the anteroseptal being the commonly hypertrophied segment. Asymmet-ric septal wall hypertrophy causes LVOT obstruction in 20–30% of cases. Asymmetric / septal HCM may be diagnosed when septal thickness is greater than or equal to 15 mm or when the ratio of septal thick-ness to the thickness of inferior wall of the left ventricle is greater than 1.5 at the midventricular level [20]. Abnormalities of the mitral valve may occur due to primary abnor-mality of the valve itself or due to LVOT obstruction. Systolic anterior motion of the mitral valve (SAM) is a phenomenon in which a por-tion of the anterior leaflet of the mitral valve distal to the coaptation gets displaced / pulled in to the LVOT by venture or drag forces, leading to transient LVOT obstruc-tion [7] (Fig. 9). Over time, the systolic anterior motion of the mitral valve leads to sub-aortic mitral impact lesion on the sep-tum which undergoes fibrosis; thickening of mitral leaflet and chordae from the resultant trauma; a posteriorly directed mitral regur-gitant jet in to the left atrium and a systolic gradient along the LVOT [18]. Patients with LVOT obstruction unresponsive to medical therapy (5%) are candidates for surgical myectomy or septal alcohol abla-tion [20]. Our patient, however, was put on medical therapy. 2) Apical HCM The apical variant of HCM shows an absolute apical thickness of > 15 mm or a ratio 1.3 to 1.5. More subjective criteria are the oblitera-tion of LV apical cavity in systole and failure to identify a normal pro-gressive reduction in LV wall thick-ness towards the apex. The left ventricle shows a charac-teristic ‘spade-like’ configuration on vertical long axis views. An apical aneurysm formation with delayed enhancement is sometimes seen referred to as the ‘burnt-out apex’ resulting from ischemia due to reduced capillary density resulting in ischemic fibro-sis. Similar appearance of ‘burnt-out apex’ is also seen in HCM causing mid- ventricular obstruction with apical aneurysm formation, as described in figure 8. The LV apex may not be assessed well with echocardiography leading to false negative interpretations. Hence cardiac MRI is strongly rec-ommended as optimal imaging modality for evaluation of apical HCM [20]. 3) HCM with mid-ventricular obstruction A variant of asymmetric HCM pre-dominantly involving the middle third of the left ventricle may result in severe mid-ventricular narrowing and obstruction. This condition may be associated with formation of an apical aneurysm which is thought to result from increased generation of systolic pressures within the apex from the mid-ventricular obstruction [18] (Fig. 8). 4) Symmetric HCM This variant is encountered in about 42% of HCM cases and is character-ized by a concentric LV hypertrophy with a small cavity dimension and no evidence of a secondary cause. This entity has to be differentiated from other causes of diffuse LV wall thickening including athlete’s heart, amyloidosis, sarcoidosis, Fabry’s dis-ease, and secondary adaptive pat-tern of LV hypertrophy due to hyper-tension or aortic stenosis, since the treatment strategies differ. Cardiac MRI is known to play an important role in differentiating other causes of myocardial hypertrophy from HCM because of the unique ability of DE MRI imaging to characterize differ-ent enhancement patterns in dis-eased myocardium [20]. Figure 7 illustrates a case of concentric HCM in a symptomatic patient. 5) Mass-like HCM Mass-like HCM manifests as a mass-like hypertrophy because of focal segmental location of myocardial disarray and fibrosis which may be differentiated from neoplastic masses. MR imaging with first pass perfusion and DE technique helps to differentiate between the two Concentric HCM in a symptomatic 35-year-old male patient. (7A, B) Short axis and vertical long axis SSFP images show symmetrically thickened LV walls (arrows) with atrial dilatation. HCM with mid-ventricular obstruction. CMR evaluation of a 55-year-old male patient with a family history of sudden cardiac deaths. (8A, B) Horizontal long axis SSFP cine MR images reveal significant hypertrophy of the LV myocardium (16–17 mm width). The thickened myocardium (asterisk in 8A) causes mid-cavity obstruction with apical thinning and outpouching resulting in a ‘dumbbell shaped LV’. (8C, D) PSIR images acquired 15 minutes post Gd administration show subendocardial LGE (solid white arrows), around 50% in the proximal areas and transmural in the apex (burnt out apex) suggestive of ischaemic fibrosis. 7A 7B 7C 7D 8A 8B 8C 8D 7 MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world 8 3A 3B (4C, D) PSIR images acquired immediately post Gd administration demonstrate perfusion defect in the LAD territory corresponding to microvascular obstruction (solid white arrows). 3C 3D 4A 4B 4C 4D 5A 5B 5C 5D An example of Diastolic septal bounce. Septal flattening / inversion seen in constrictive pericarditis, since outward expansion of the right ventricle is limited by a non-compliant pericardium. (6A) Shows IV septum in mid systolic phase. (6B) Diastolic phase reveals mild leftward bowing of the septum. 6 5 MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world 6 the LAD, 10 in the RCA and 4 in the LCX territories, corresponding to non-viable myocardium (Table 3). 11 patients demonstrated < 50% of myocardial LGE. Of these, 5 belonged to LAD territory and 2 and 4 to the LCX and RCA territories, respectively (Table 3). On follow up, 7 patients underwent revascularisation procedures. All of these reported to experience symp-tomatic relief. 15 patients were evaluated for cardio-myopathy. All patients with CMP are managed by medical therapy and are doing well. We evaluated 2 patients for constric-tive pericarditis. Both were started on anti-Koch’s therapy and are symp-tomatically better. 5 patients were referred for evalua-tion of cardiac masses after an echo-cardiographic study. 3 of these had revealed a LV clot and 1 patient had demonstrated a nodular mass attached to the LV wall. One patient suspected to have a mass posterior to left atrium on echocardiography was diagnosed with straight back syndrome with the thoracic vertebral body indenting the left atrium. LV clots were confirmed on CMR and the patients were put on anticoagulation therapy. One patient diagnosed as LV myxoma being managed on medical therapy, is doing well. Discussion A) Myocardial viability Ischemic heart disease (IHD) is today one of the leading causes of death all over the world. Cardiac MRI plays an important role com-plementary to other imaging modalities in evaluation of patients with IHD. Myocardial infarction results from rupture of an athero-sclerotic plaque in a coronary artery leading to thrombus formation. The subendocardium is most vul-nerable to ischemia and an infarct expands form subendocardium to subepicardium [7]. Myocardial infarction, scarring and viability are simultaneously exam-ined using technique of delayed enhancement MRI. Delayed / late gadolinium hyper-enhancement is caused by delayed washout of contrast agent from the myocardium. Delayed enhancement is performed 10–15 minutes after i.v. administration of 0.15 to 0.2 mmol/kg of gadolinium. An inversion recovery sequence is used in which normal myocardium is nulled to accentuate the delayed enhancement [7]. Both acute and chronic infarctions enhance. In acute infarctions, con-trast enters the damaged myocar-dial cells due to membrane disrup-tion (microvascular obstruction / no reflow zones). These regions are recognised as dark central areas surrounded by hyperenhanced necrotic myocardium. This finding indicates the presence of damaged microvasculature in the core of an area of infarction. The presence of a ‘no-reflow’ zone appears to be associated with worse LV remodel-ling and outcome [7, 9]. CMR can be safely carried out in patients with acute MI and primary angio-plasty and aids in risk stratification. T2-weighted imaging allows the detection of myocardial edema, allowing for early diagnosis of myo-cardial ischemia, area at risk, and salvage [22] (Fig. 4). In chronic infarctions, the LGE is a result of retention of contrast medium in large interstitial space between collagen fibres in the fibrotic tissue. Stunning and hibernating myocardium Cine imaging in combination with delayed enhancement MRI allows identification of: 1) Myocardial stunning: Stunning is defined as post-ischemic myocardial dysfunction (seen in the setting of acute myocardial ischemia) which persists despite restoration of normal blood flow. Over time there can be a gradual return of contractile func-tion depending on transmurality of the ischemia. If the degree of trans-murality as seen on delayed enhancement images is < 50%, the myocardial function is likely to recover. 2) Hibernating myocardium: A state in which some segments of the myocardium exhibit abnormalities of contractile function at rest. This phenomenon is clinically significant since it manifests in the setting of chronic ischemia that is potentially reversible by revascularisation. The reduced coronary perfusion causes the myocytes to enter into a low energy ‘sleep mode’ to conserve energy. There is an inverse relation-ship between transmural extent of hyperenhancement, and likelihood of wall motion recovery following revascularisation [5]. Multiple experimental studies have demonstrated excellent spatial correla-tion between the extent of hyper-enhancement and areas of myocardial necrosis (acute MI) or scarring (chronic MI) at histopathology. Specifically, there is an inverse rela-tionship between transmural extent of hyperenhancement and likelihood of wall motion recovery following revas-cularisation. Hence it follows that myocardial regions which show little or no evidence of hyper-enhancement (i.e. infarction) have a high likelihood of recovery, whereas regions with transmural hyperenhancement have virtually no chance of recovery [9]. Moving from a 1.5T to a 3T system involves doubling of SNR which can be used to increase either spatial or tem-poral resolution. This translates into potentially increased contrast between perfused and non-perfused images leading to increased contrast-to-noise ratio (CNR) with better LGE in setting of chronic ischemia [1]. Figures 1–3 demonstrate LGE in the RCA & LCX, LCX and LAD territories, respectively, significant other non-via-ble myocardium in these regions. Table 3 Transmural extent LAD LCX RCA > 50% 30 4 10 < 50% 5 2 4 Table 4 Indications Number of patients 1) Myocardial viability 55 2) Recent MI 2 3) Cardiomyopathies 15 a) Hypertrophic cardiomyopathy 8 b) Dilated cardiomyopathy 5 c) Non compaction cardiomyopathy 2 d) Restrictive cardiomyopathy 1 4) Cardiac masses 5 5) Congenital heart disease 1 6) Pericardium (constrictive pericarditis) 2 Table 5 [9]: Differentiation between acute and chronic MI. Acute MI Chronic MI Bright on pre-contrast STIR (or T2w) imaging Not bright on pre-contrast STIR(or T2w) imaging Walls may be thicker than usual Walls may be thinned May have a ‘no-reflow zone’ Does not have a ‘no-reflow zone’ Myocardium protected by collateralisation Myocardium capable of reperfusion No reflow territory / microvascular obstruction PSIR short axis image acquired immediately post Gd administration in a 60-year-old female patient reveals suben-docardial 1st pass defect in the lateral wall (solid white arrow). PSIR images taken 15 minutes after Gd admin-istration reveal subendo-cardial LGE with trans-mural extent suggestive of non-viable myocardium in the LCX territory (solid white arrow). 2A 2B Cardiology Clinical MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world 4 Clinical Cardiology 3 MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world Abstract Diagnostic clinical cardiac magnetic resonance imaging (MRI) requires an appropriate combination of temporal and spatial resolution. Cardiovascular imaging is making considerable advances toward the fulfillment of these requirements, largely because of continued improvements in MRI hardware and software. Optimal diag-nostic- quality MRI implies a balance among signal-to-noise ratio (SNR), tissue contrast, acquisition time, and spatial and temporal resolution. Mag-netic field strength is one of the major factors affecting image SNR [3]. The transition from 1.5T to 3T has resulted in faster imaging and better SNR. However, cardiac MRI protocols on 3T have not yet been optimized in the way that they have been optimized for 1.5T over the last decade. This article illustrates 80 cases of car-diac MRI imaged on a 3T MRI system (MAGNETOM Verio, 32-channel sys-tem) at our institution done between January 2012 and August 2013. This is probably the largest study of car-diac MRI done on a 3T in India. Introduction The role of magnetic resonance imaging (MRI) has significantly evolved over the last decade. MRI is now considered useful in the evalua-tion of pericardium, complex congen-ital heart disease, cardiac masses, and ischemic heart disease for myo-cardial viability, hibernating and stunned myocardium and the right ventricle. In 2002, the US Food and Drug Administration’s (FDA) approval of 3 Tesla opened the way for multiple clinical applications. Compared to 1.5T, the higher field strength results in doubling of SNR due to increased spin polarisation. Furthermore, imag-ing at higher field strengths with gad-olinium- based agents can produce fur-ther improvements in image contrast. Cardiac imaging at 3T is, however, noticeably different from imaging at 1.5T because of a variety of artifacts that result from susceptibility effects and augmentation of radiofrequency (RF) inhomogeneity [3]. The adoption of 3T for body applica-tions, especially cardiac applications, has been somewhat slower. The slower acceptance of 3T for cardiac applications is due to the unique chal-lenges posed by cardiac imaging: Requirement of a large field-of-view, the motion of the heart, position of the heart within the body, proximity of heart to the lungs, and high RF power deposition required in many fast car-diac imaging sequences [1]. Cardiac MRI has largely been done on a 1.5T in India. Due to optimization done on 1.5T and apprehension of challenges on a 3T system, no significant work was done on 3T in India. We present probably the largest number of cardiac MRI cases performed till date on a 3T in India. There are several advantages which motivate users to perform cardiovascu-lar magnetic resonance (CMR) at higher filed strengths. First, the bulk magnetisation increases as the mag-netic field strength is increased result-ing in higher SNR. Second, the increas-ing field strength increases the frequency separation of off-resonance spins. The enhanced frequency differ-ences may be exploited for improve-ment in spectroscopic imaging and potentially in fat suppression. A third advantage is increased T1 signal of many tissues, resulting in beneficial effects in some applications, such as myocardial tagging and myocardial perfusion sequences [1]. Methods and Materials A) Patient population Eighty patients with an age range of 5 to 70 years with a suspected cardiac pathology were evaluated by cardiac MRI (CMR) at our institute from January 2012 to August 2013. All patients had undergone a prior echocardiography. B) Patient preparation A detailed history was elicited from each patient including principal symptoms and signs, echocardio-graphic and cardiac catheterisation data. For all patients in this study, MR compatible electrocardiographic leads were placed in the anterior chest wall before imaging and attached to the MR imaging unit for electrocardiographic gating. For most sequences, electrocardio-graphic triggering was used to syn-chronise imaging with the onset of systole and offset cardiac motion and match each image to the desired cardiac phase. C) Cardiac MRI protocol Cardiac MRI was performed using a whole-body 3T scanner (MAGNETOM Verio, Siemens Healthcare, Erlangen, Germany). MR imaging protocol commenced with a localiser using TrueFISP (steady-state free precision) sequence. A list of protocols is given in table 2. Axial and coronal scans of 5 mm slice thickness were obtained from the aortic arch to diaphragm. All diagnostic sequences were acquired in stan-dard angulations (4-, 2-chamber view and short axis) using a matrix of at least 256 × 256. Myocardial function was evaluated by cine TrueFISP sequences; T2-weighted dark blood turbo spin echo sequences were acquired 5 and 15 minutes after injection of 0.15 mmol gadolinium diethylene triamine penta-acetic acid (DTPA) (Magnevist, Schering, Berlin, Germany) per kilogram of body weight. Inversion recovery prepared turbo sequences (FLASH and TrueFISP) were performed to visualise the myocardial and blood pool gadolinium kinetics, and to adjust inversion time. An inversion time (TI) scout was acquired and the optimal TI value was found. Endocardial counters of the left ven-tricle were manually drawn using dedicated software (Argus, Siemens Healthcare, Erlangen, Germany) to calculate end-diastolic volume, end-systolic volume, stroke volume and ejection fraction of the left ventricle [8]. In the case of evaluation of con-genital heart diseases, scans were obtained till below the diaphragm including IVC and the hepatic veins [23]. A summary of the basic cardiac protocols is presented in table 1. Modified sequences were acquired for specific indications which have been summarised in table 2. D) Results The study comprised 80 patients. The age range was 5 to 70 years. There were 57 male and 23 female patients. The commonest indica-tion for a CMR study was evalua-tion of myocardial viability. The variety of indications for which cardiac MRI was performed is summarised in table 4. Images were analysed by one radi-ologist and one cardiologist. The morphological information com-prised of chamber anatomy, thick-ness of the ventricular walls and assessment of presence and extent of late gadolinium hyper-enhance-ment on delayed post contrast PSIR images. Functional information comprised of assessment of wall motion abnormalities, calculation of ejec-tion fraction and evaluation of the outflow tracts. In cases of congenital heart dis-ease, cine imaging in horizontal long axis provided dynamic infor-mation of the cardiac size, valve morphology, wall thickness cham-ber size, and septum morphology and aortopulmonary connections [23]. 55 patients were referred for eval-uation of myocardial viability. Of these, 30 showed transmural late gadolinium enhancement (LGE) in 68-year-old male patient imaged for evaluation of myocardial viability. PSIR sequence taken 15 minutes post Gd administration reveals transmural LGE in the inferior wall conforming to RCA and the LCX territory (solid white arrows) suggestive of non-viable myocardium. Horizontal long axis view of the same patient showing the extent of transmural LGE. 1A 1B Cardiology Clinical MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world 2 Clinical Cardiology 1 MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world Reprinted from MAGNETOM Flash 5/2013
- 19. Myocardial Tissue Imaging Using Simultaneous Cardiac Molecular MRI James A. White, M.D., FRCPC The Lawson Health Research Institute, London, Ontario, Canada Molecular MRI in London Ontario The Lawson Health Research Institute (the “Lawson”) is located within St. Joseph’s Healthcare in London Ontario, and is affiliated with West-ern University. This group received the first Biograph mMR in Canada in March 2012. With strong existing research groups in MRI and nuclear medicine this group is ideally posi-tioned to drive research and innova-tion using this platform. In advance of the installation of the hybrid molecular MR, researchers at the Lawson had been developing novel MR-based attenuation correction methods, and novel tracer develop-ments. In addition to the molecular MR this site has a PET-CT, a SPECT-CT, and an Inveon small animal PET as well as two 1.5T MAGNETOM Aera systems, a 16.5MeV medical cyclo-tron and radiochemistry facilities. Myocardial tissue imaging Hybrid imaging platforms incorporat-ing PET have become available for cardiovascular imaging applications over the past decade. These platforms have been primarily aimed at provid-ing superior tissue attenuation correc-tion of the emitted photon signal and to provide spatial anatomic registra-tion for the localization of abnormal tracer signal. While this has resulted in substantial improvements in the clini-cal performance of cardiac PET, the exploitation of complementary imag-ing data has yet to be fully realized. The recent availability of hybrid plat-forms allows for an expansive range of PET applications to be explored. For example the capacity of cardiovas-cular MRI to provide complementary 2D and 3D morphological data with excellent soft tissue contrast and high temporal resolution is of benefit for anatomic registration and novel motion correction algorithms. However, its incremental capacity to provide exqui-site tissue characterization through intrinsic tissue contrast and altered kinetics of exogenous paramagnetic contrast is of particular interest in the context of the PET imaging environment. Clinical adoption of myocardial tissue imaging is expanding in response to mounting evidence that the ‘health’ of myocardium strongly modulates bene-fit from heart failure therapies (phar-macologic, surgical and device-based) and is predictive of future arrhythmic events among patients with ischemic and non-ischemic cardiomyopathy [1-5]. To date, this literature has focused on isolated and disparate markers of tissue health using both PET and MRI. However, within this brief report we discuss several synergies of these platforms that hold promise towards a new era of hybrid imaging for the optimal performance of myocardial tissue imaging. Molecular MRI in the setting of acute ischemic injury Among those surviving acute myocar-dial infarction (AMI), appropriate myo-cardial healing is believed to be reliant upon a highly choreographed process of early inflammatory cell invasion, collagen degredation, debris removal by activated macrophages, and myofibroblast proliferation with reconstitu-tion of a new collagen matrix. While 1 1 The Lawson Health Research Institute. 2A 2B 2C Example of a non-reperfused myocardial infarction from LAD ligation in a canine model, imaged one week post ligation. A large area of microvascular obstruction (MO) is seen by LGE imaging with a corresponding marked prolongation of T1 shown using MOLLI-based T1 mapping. Simultaneously acquired FDG imaging (binned to cardiac phase) has been fused to both LGE imaging and raw T1 map and illustrates a marked reduction in inflammation within the region of MO. There is intense inflammatory activity evident within the perfused infarct rim. such findings can be characterized histologically, our capacity to quantify markers of the inflammatory process in vivo, and evaluate influences of its modulation on the remodeling process has been limited. We have started examining this pro-cess in a canine infarct model using the Biograph mMR 3T-PET platform using simultaneous 3D LGE / 18F-FDG imaging, the latter imaged following normal myocardial glucose metabolism using intravenous heparin and lipid infusion. In these experiments we have focused on evaluating the influence of microvascular obstruction (MO) on mitigating appropriate inflammatory cell recruitment to the infarct core – a postulated mechanism of how MO may adversely impact on left ventricu-lar remodeling post infarct. Figure 2 illustrates how the region of MO can be elegantly visualized using both LGE imaging and T1 mapping CMR techniques. 18F-FDG imaging shows intense inflammatory activity within the perfused infarct rim, however a marked reduction in activity is seen in regions of MO. This imaging may therefore provide novel insights towards mechanisms by which MO contributes to adverse outcomes fol-lowing AMI, and offers a new tool to evaluate therapies aimed at modu-lation of this pathway. Molecular MRI in the setting of acute non-ischemic (inflammatory) injury Both PET and CMR have been investi-gated for their diagnostic accuracy in the setting of suspected inflamma-tory cardiomyopathy – particularly among patients with known pulmo-nary Sarcoid. While their respective diagnostic performance has been compared in the past, this remains inappropriate, as the information gathered and interpreted from each technique could not be more unique. PET imaging (typically performed using 18F-FDG following prolonged fasting, fatty meal consumption and intravenous heparin to suppress nor-mal myocardial glucose utilization) exploits the hypermetabolic signal of activated inflammatory cells (i.e. macrophages) and therefore indi-cates disease ‘activity’ among patients with active cardiac Sarcoid. In con-trast, LGE imaging indicates regions of mature granulomatous fibrosis among patients with prior or current cardiac Sarcoid. Therefore, these two commonly employed diagnostic tech-niques provide complementary but unique information. 2 LGE T1-map (raw) T1-map (color) LGE / FDG FDG (raw) T1-map/FDG 2D 2E 2F Cardiology Clinical MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world 37 Clinical Cardiology 36 MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world
- 20. Clinical Cardiology Cardiology Clinical Figure 3 illustrates the capacity of hybrid MR and PET to spatially register these techniques using simultane-ously acquired data, and potentially improve diagnostic accuracy while expanding our understanding of dis-ease pathophysiology. In this case of a 72-year-old female presenting with heart failure and non-sustained ventricular tachycardia we can iden-tify a leading edge of inflammation (intense FDG uptake) with a trailing edge of irreversible injury or ‘scar’ (indicated by hyperenhancement on LGE imaging) at the sub-epicardial zone. This approach ushers in a new era of imaging for inflammatory-mediated disease where a more com-plete spectrum of disease activity can be visualized in a single, spatially registered examination. Molecular MRI in the setting of non-acute myocardial disease Another clinical setting where MR and PET have established their respec-tive roles for therapeutic decision-making is for the assessment of tissue viability in chronic ischemic cardiomyopathy. Evidence supports that both the regional reduction of FDG signal [6, 7] and regional scar transmurality by LGE are strongly predictive of absence of functional recovery following coronary revas-cularization. The performance of these studies are therefore commonly considered to be mutually exclusive, with absence of FDG signal being the sine qua non of myocardial scar, and the lack of scar by LGE imaging being equivalent to tissue health. However, it is recognized that the spatial resolution and signal-to-noise of LGE imaging is superior to FDG for the detection of subendocar-dial scar, and also for the character-ization of tissue viability among those with marked thinning of the ventricular wall [8]. Conversely, FDG-PET based metabolic abnormalities can be documented within tissue that fails to demonstrate myocardial scar on LGE MRI, lack of FDG uptake being predictive of absence of func-tional recovery. Accordingly, the marriage of PET-based metabolic imag-ing and LGE-based scar imaging may provide a more robust platform for the prediction of improved outcomes following coronary revascularization. In figure 4 we see a 42-year-old male referred for viability imaging prior to coronary artery bypass surgery late following myocardial infarction. Cine imaging shows a large region of thinned and akinetic myocardium in the distribution of the left anterior descending artery, this territory dem-onstrating varying degrees of trans-mural scar following gadolinium administration. Simultaneous MR and PET with 18F FDG imaging shows meta-bolic activity within non-scarred regions surrounding the infarct zone and normal metabolic tracer activity within remote myocardium. 4 42-year-old male with large anterior wall myocardial infarction being considered for surgical revascular-ization in the setting of triple vessel disease. Cine MRI shows akinesia of the septum and apex with a reduced ejection fraction of 32%. Late gadolinium enhancement (LGE) imaging shows a large infarct of the LAD territory with variable scar trans-murality ranging from 25% to 100% throughout the infarct region. FDG-PET imaging, shown fused with LGE imaging, shows matched reductions in metabolic tracer uptake. 72-year-old female with suspected new-onset heart failure and non-sustained ventricular tachycardia and prior history of biopsy- proven systemic Sarcoid. Top rows show late gadolinium enhancement (LGE) imaging with characteristic sub-epicaridal based scar (arrows), consistent with prior inflammatory injury. Lower row shows fused FDG-PET images with evidence of focal signal enhancement, consistent with active inflammation surrounding regions of established scar. 3 References 1 Gulati A, Jabbour A, Ismail TF, Guha K, Khwaja J, Raza S, Morarji K, Brown TD, Ismail NA, Dweck MR, Di Pietro E, Roughton M, Wage R, Daryani Y, O’Hanlon R, Sheppard MN, Alpendurada F, Lyon AR, Cook SA, Cowie MR, Assomull RG, Pennell DJ, Prasad SK. Association of fibrosis with mortality and sudden cardiac death in patients with nonischemic dilated cardiomyopathy. JAMA. 2013;309:896-908. 2 Gao P, Yee R, Gula L, Krahn AD, Skanes A, Leong-Sit P, Klein GJ, Stirrat J, Fine N, Pallaveshi L, Wisenberg G, Thompson TR, Prato F, Drangova M, White JA. Prediction of arrhythmic events in ischemic and dilated cardiomyopathy patients referred for implantable cardiac defibrillator: Evaluation of multiple scar quantification measures for late gadolinium enhancement magnetic resonance imaging. Circ Cardiovasc Imaging. 2012;5:448-456. 3 Kwon DH, Halley CM, Carrigan TP, Zysek V, Popovic ZB, Setser R, Schoenhagen P, Starling RC, Flamm SD, Desai MY. Extent of left ventricular scar predicts outcomes in ischemic cardiomyopathy patients with significantly reduced systolic function: A delayed hyperenhancement cardiac magnetic resonance study. JACC Cardiovasc Imaging. 2009;2:34-44. With Chronic Ventricular Dysfunction Due to Coronary Artery Disease: A Meta-Analysis of Prospective Trials. J. Amer. Coll Cardiol Img 2012;5:494 -508. 7 Lee Fong Ling, Thomas H. Marwick, Demetrio Roland Flores, Wael A. Jaber, Richard C. Brunken, Manuel D. Cerqueira and Rory Hachamovitch. Identification of Therapeutic Benefit from Revascularization in Patients With Left Ventricular Systolic Dysfunction : Inducible Ischemia Versus Hibernating Myocardium. Circ Cardiovasc Imaging 2013;6;363-372. 8 Klein C, Nekolla SG, Bengel FM, Momose M, Sammer A, Haas F, et al. Assessment of myocardial viability with contrast-enhanced magnetic resonance imaging: Comparison with positron emission tomography. Circulation 2002;105:162-7. Contact James A. White, M.D., FRCPC Robarts Research Institute P.O. Box 5015, 100 Perth Drive London ON, Canada N5K 5K8 Phone: +1 519-663-5777 jawhit@ucalgary.ca 4 Klem I, Shah DJ, White RD, Pennell DJ, van Rossum AC, Regenfus M, Sechtem U, Schvartzman PR, Hunold P, Croisille P, Parker M, Judd RM, Kim RJ. Prognostic value of routine cardiac magnetic resonance assessment of left ventricular ejection fraction and myocardial damage: An inter-national, multicenter study. Circ Cardiovasc Imaging. 2011;4:610-619. 5 Neilan TG, Coelho-Filho OR, Danik SB, Shah RV, Dodson JA, Verdini DJ, Tokuda M, Daly CA, Tedrow UB, Stevenson WG, Jerosch-Herold M, Ghoshhajra BB, Kwong RY. CMR quantification of myocardial scar provides additive prognostic information in nonischemic cardiomyopathy. JACC Cardiovasc Imaging. 2013;6:944-954. 6 Romero, J, Xue X, Gonzalez W, Garcia MJ. CMR Imaging Assessing Viability in Patients 3A 3B 3C 3D 3E 3F 4A 4B 4C 4D 38 MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world MAGNETOM Flash | 1/2014 | www.siemens.com/magnetom-world 39
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