093 multi slice fast ct

Multi-slice fast CT and Electron
Beam Tomography: the first
screening step in imaging
coronary atherosclerosis?
Stephan Achenbach, MD
Department of Cardiology,
University of Erlangen, Germany

Coronary artery disease events such as myocardial infarction or coronary death frequently
occur in previously healthy individuals without prior symptoms. Tests which permit
identification of individuals at increased risk may thereore be beneficial.
Since coronary events are in most cases caused by plaque rupture, imaging
methods which permit the identification and quantification of coronary atherosclerotic
plaque are potentially useful for risk stratification. Most non-invasive imaging techniques,
however, lack the combination of high temporal and spatial resolution which is necessary
to reliably visualize the coronary arteries.
Electron beam tomography (EBT) and, more recently, multi-slice spiral CT
have been shown to permit visualization and quantification of coronary calcium in a non-
invasive fashion. Coronary calcium is always caused by coronary atherosclerosis and the
amount of coronary calcification correlates to the overall atherosclerotic plaque burden.
Numerous clinical studies conducted by electron beam tomography have proven the
method´s potential to identify individuals at increased risk for coronary events through
detection and quantification of coronary calcifications. Most (but not all) studies have
demonstrated a higher predictive value of coronary calcifications as compared to
traditional risk factors. Even though some smaller studies have shown that mulit-slice CT
(MSCT) in conjunction with ECG-gated reconstruction techniques permits the detection
and quantification of coronary calcium with accuracies similar to electron beam
tomography, no clinical outcome data have so far been published using MSCT.
In conclusion, the detection and quantification of coronary calcification my be
a useful tool for the identification of individuals at increased risk for coronary events.
Abstract:

Coronary events - such as
myocardial infarction - are
usually caused by plaque
rupture and frequently occur
in previously asymptomatic
individuals
Introduction

Traditional risk factors
frequently do not permit
satisfactory identification of
individuals who are at
increased risk for coronary
artery events
Introduction

Imaging techniques for the non-
invasive detection of atherosclerotic
plaque in the coronary arteries may be
helpful to identify individuals at
increased coronary event risk.
However, both high temporal and high
spatial resolution are necessary to
visualize the corornary arteries in a
non-invasive fashion.
Introduction

Electron beam
tomography is a
cross-sectional x-
ray imaging
technique with a
temporal
resolution of 100
ms.
Introduction

Electron beam
tomography
permits the
sensitive detection
and quantification
of coronary artery
calcification.
Calcium in LAD & LCX
Calcium in RCA
Introduction

Aquisition
protocols and
methods for
quantification of
coronary calcium
by EBT are
standardized and
large reference
data bases are
available1, 2
.
Severe calcification in LAD
Abscence of coronary
Introduction

Recent pre-clinical
work has shown that
multi-slice spiral CT
using the last
hardware generation
and sophisticated
ECG-correlated
image reconstruction
software also permits
coronary calcium
detection4,5
.
LAD calcifications in
retrospectively ECG-gated
multislice CT
Introduction

Introduction
However, care has to be taken in order to avoid motion artifacts
which may be more frequent due to the longer acquisition window
as compared to EBT
Same patient: prospectively triggered (left) and retrosplectively triggered MSCT

What is the rationale
behind the detection of
coronary artery
calcification?
Discussion

Why detect coronary calcium?
Coronary calcification is
always caused by
artherosclerosis 6
Discussion

Why detect coronary calcium?
The amount of
calcium correlates
to overall plaque
burden 7,8
However: no close relationship between calcium in a
vessel segment and degree of luminal stenosis.
Discussion

Even though calcium
does not permit to
specifically detect
vulnerable plaque, it
is wrong to assume
that calcified plaques
are stable or more
frequently stable
than non-calcified
plaques9
.
erosion
stable
vulnerable
healed
rupture acute
rupture
Presence of Calcium
Discussion

Discussion
Coronary calcium does not permit to
detect the „vulnerable plaque“, but it
permits to detect the patient with high
coronary atherosclerotic plaque burden
in an asymptomatic stage.

A number of clinical trials have
evaluated the predictive value of
coronary calcium detection by
electron beam tomography in
symptomatic and asymptomatic
individuals.
Discussion

Raggi et al10
:
632 asymptomatic patients
32 +/- 7 months follow-up
myocardial infarction and death
Annual event rate:
0.1% for calcium score of 0
2.1% for calcium score 1-99
4.1% for calcium score 100-400
4.8% for calcium score > 400
Raggi et al, Circulation 2000
Discussion

Arad et al11
:
1173 asymptomatic patients
1 year and 3.5 year follow-up
Risk ratio for coronary events: 23 for calcium
score > 160
Discussion

Meta analysis by O´Malley et al12
:
Calcium score above
median:
All events: RR 8.6
„Hard“ events: RR 4.2
Discussion

Discussion
In most studies, coronary calcium by EBT
was more predictive than conventional risk
Arad et al 1996: ROC 0.91 for calcium, 0.74 for RF
1173 asymptomatic subjects (mean age: 53 years)
Raggi et al 2000: OR 22 for calcium, 7.0 for RF
632 asymptomatic subjects (mean age: 52 years)
Detrano et al 1999: ROC 0.65 for calcium, 0.67 for RF
1196 asymptomatic high-risk subjctes (mean age: 67 years)

Keelan et al13
:
288 patients with CAD who underwent coronary
angiography. Follow-up 6.9 years.
Event-free survival was significantly higher for patients
with calcium score < 100 than for those with scores > 100.
Discussion

In summary, a number of studies have proven the
prognostic value of coronary calcium detection by
electron beam tomography in asymptomatic and
symptomatic populations.
Study results are not completely unanimous
concerning the superiority of coronary calcium
over traditional risk factors, but most studies
found coronary calcium to have a higher
predictive value.
No clinical outcome studies have so far been
performed using multi-slice CT.
Discussion

What is the potential clinical role of coronary
calcium detection?
AHA/ACC statement14
:
„A positive EBCT confirms the presence of coronary atherosclerotic
plaque.“
„Total amount of calcium correlates ... total amount of
atherosclerotic plaque.“
„A negative EBCT test makes the presence of atherosclerotic plaque,
including unstable plaque, very unlikely.“
„A high calcium score may be consistent with a moderate to high
cardiovascular event risk within 2-5 years.“
„A negative test ... low risk of a cardiovascular event in the next 2 to
5 years.“
Discussion

calcium detection?
In clinical practice, cleary low-risk and clearly
high-risk individuals probably do not need further
testing for risk stratification.
Intermediate risk patients, however, might profit:
ACC/AHA14
: „selected use of coronary
calcium scores when a physician is faced
with the patient with intermediate
coronary artery disease risk may be
appropriate“
Discussion

calcium detection?
Discussion

Role of EBT and MSCT in risk stratification?
Coronary calcium, even though it does not permit
to detect the „vulnerable plaque“, permits to
identify the patient with high plaque burden.
The detection of coronary calcium
therefore permits identification of
patients at increased risk for
coronary artery events.
It may be beneficially applied in
patients who seem to be at
„intermediate“ risk.
Conclusion

Initial results have shown that EBT and especially
MSCT - after i.v. injection of contrast agent - also
permit visualization of non-calcified plaque:
Partly calcified plaque in the
proximal right coronary
artery visualized by multi-
slice CT MSCT
Conclusion

Non-calcified plaque in EBT:
EBT EBT
Conclusion

Non-calcified plaque in MSCT:
Conclusion

Some authors have compared plaque
morphology in MSCT to intravascular
ultrasound15
, but the clinical
implications and the exact meaning of
non-calcified plaque in MSCT or
EBBT currently are not clear.
Conclusion

SUMMARY:
EBT and MSCT have sufficient spatial and
temporal resolution for coronary artery
visualization.
Clinical studies have shown a high prognostic
value of coronary calcium for identification of
asymptomatic individuals at increased coronary
artery disease risk.
The meaning of non-calcified plques which can
also be detected (after injection of contrast agent)
is not yet clear.
Conclusion

SUMMARY:
Future clinical studies, some are currenty being
conducted, will help to define the role of coronary
calcium detection in the clinical work-up of
patients ín whom risk stratification for coronary
artery events may be beneficial.
Conclusion

References
1. Hoff JA, et al: Age and gender distributions of coronary artery calcium detected by
electron beam tomography in 35246 adults. Am J Cardiol 2001;87:1335-1339
2. Raggi P: Introduction. Am J Cardiol 2001:88(2A);1E-3E.
4. Carr JJ, et al: Coronary artery calcium quantification with retrospectively gated
helical CT: protocols and techniques. Int J Card Imaging 2001;17:213-220
5. Becker CR, et al: Coronary artery calcium measurement: agreement of multirow
detector and electron beam CT. Am J Roentgenol 2001;176:1295-1298
6. Blankenhorn DH: Coronary arterial calcification. Am J Med Sci 1961; 41-50
7. Rumberger JA, et al: Coronary artery calcium area by electron-beam computed
tomography and coronary atherosclerotic plaque area. A histopathologic correlative
study. Circulation 1995:92:2157-2162.

References
8. Sangiorgi G, et al: Arterial calcification and not lumen stenosis is highly correlated
with atherosclerotic plaque burden in humans: a histologic study of 723 coronary artery
segments using nondecalcifying methodology. J AM Coll Cardiol 1998;31:126-133
9.Burke et al: Coronary calcification: insights from sudden coronary death victims. Z
Kardiol 2000;89(Suppl. 2):49-53
10. Raggi P et al: Identification of patients at increased risk of first unheralded acute
myocardial infarction by electron-beam computed tomography. Circulation
2000;101:850-855
11. Arad Y et al: Prediction of coronary events with electron beam computed
tomography. J Am Coll Cardiol 200:36:1253-1260
12. O´Malley et al: Prognostic value of coronary electron-beam computed tomography
for coronary heart disease events in asymptomatic populations. Am J Cardiol
2000;85:945-948
13. Keelan PC et al: Long-term prognostíc value of coronary calcification detected by
electron beam computed tomography in patients undergoing coronary angiography.
Circulation 2001;104:412-417
14. ACC/AHA expert consensus document on electron-beam computed tomography
for the diagnosis and prognosis of coronary artery disease. Circulation 2000;102:126-
140
15. Kopp AF et al: Non-invasive characterization of coronary lesion morphology and
composition by multislice CT: first results in comparison with intracoronary ultrasound. Eur Radiol
2001:1607-1611

093 multi slice fast ct

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