Quality Assurance Programme in Computed Tomography

Outline
 Introduction to Computed Tomography
 Component of CT System
 CT Data Acquisition System
 Quality Assurance in CT
 QA/QC Test in CT
 Conclusion
 References

Computed Tomography
Is a medical imaging procedure of creating
a cross-sectional tomographic plane of any
part of the body .
CT scanners create cross-sectional images of high radiographic contrast
The dose to the patient may be significantly higher than with
alternative imaging modalities

Computed Tomography
Component of CT System
Computer (Operating Console)
Gantry and Table
X-ray Tube
Filter
Detector

Computed Tomography
Computer
Provides the link between the CT technologist and the other
components of the system.
Control of data acquisition,
Image reconstruction,
Storage of image data, and
Image display

Computed Tomography
Gantry and Table
A circular device that house the;
 The X-ray tube
The Detector Array
Data Acquisition System
The Generator

Computed Tomography
Gantry and Table continue…
The table is a flat or slightly curved platform that the patient lies on
during the scan.
The table is responsible for positioning the patient with the gantry
The patient couch on the table must be constructed of low Z-material,
such as carbon fiber to not interfere with x-ray beam transmission
and patient imaging.

Computed Tomography
X-ray Tube
They have an anode heat storage
capacity of 4-5 MHU (million heat
unit) or more.
CT x-ray tube use a rotating anode to
increase heat dissipation

COMPUTED TOMOGRAPHY
Detector
The detectors in CT function as image receptors.
It measures the amount of radiation transmitted
through the body and converts the measurement into
an electrical signal.
The two basic detector types used in CT are scintillation
(solid state) and ionization (xenon gas) detectors
Detector
Rings

Computed Tomography
Data Acquisition System
X-ray photons come on the detector.
The detector detects the intensity in form of current.
The current is converted into voltage.
The analog signal is converted into digital form.
This signal can now be processed and reconstructed in the computer
Detector
Current to
Voltage
Convertor
Pre
Amplifier
Analog to
Digital
Convertor
Computer

Quality Assurance
Quality assurance (QA) is a program used by management to maintain
optimal diagnostic image quality with minimum hazard and distress to
patients.
The program includes;
Periodic quality control tests,
Administrative Procedure
Corrective action and
Training

QA/QC Test In CT
Field Uniformity Test
Data Analysis
Daily Test Objective
Equipment Warm-up Test To ensure equipment is working properly
CT Number for Water To ensure consistency for CT calibrated number for water
Field Uniformity Test To evaluate the scan plane uniformity

QA/QC Test In CT
Monthly Test Objective
CT Light Alignment Test To ensure that the internal and external alignment lights are properly aligned
with the tomographic plane and the couch
SPR Accuracy To ensure that the SPR image accurately indicates the patient position
CT Number Accuracy, Image
Noise, Uniformity And
Image Artifacts
To ensure a) CT number accuracy; b) Noise levels of CT images being within the
tolerances with respect to their reference values; c) Uniformity of CT number
and image noise across the FOV; d) Minimal image artefacts
Image Display and Printing To confirm that the image displays are reproducing all of the grey scale
information in the image accurately and that the printed images are a true
replica of the image display
Low Contrast Resolution
Test
To determines the capability of the scanner to discriminate low contrast objects
High Contrast Spatial
Resolution
To determines the high contrast spatial frequency limits of the CT scanner under
various conditions
Scan Increment Accuracy To determines the deviation of indicated versus actual scan increment

QA/QC Test In CT
Annual Test Objective
Visual Inspection and
Programme Review
1. To ensure that the CT scanner and adjacent areas are safe and have the necessary
radiation protection supplies
2. To ensure that CT QC test are being conducted at appropriate time periods and
corrective actions are taken when necessary
X-ray Generator If the patient dose is excessively high, then kV and HVL should be investigated to
determine the cause of high dose
Radiation Dose 1. To Compare the determined CVOL (CTDVOL) with the manufacturer’s specification.
2. To determine the CVOL (CTDIVOL) and CT (DLP) values for selected protocols
representing the main examinations clinically performed at the facility
3. To Review and update the CVOL (CTDIVOL) and CT (DLP) values for selected
protocols representing the main examinations clinically performed at the facility
X-ray Beam Width To determine the accuracy of collimator settings
Spatial Resolution To ensure that the spatial resolution of a reconstructed image complies with
manufacture standards

QA/QC Test In CT
Software
Spatial/geometry accuracy tests
oCorrect data transfer
Image Registration
Image reconstruction
oTests should verify that the software accurately reconstructs known
phantoms

QA/QC CT Test Phantom
Line Pair High Contrast Phantom Siemens Phantom
CT number regions in RMI
ACR accreditation phantom
RMI Model 464
Head and body dosimetry
phantoms

Conclusion
The QA program is designed to improve accuracy of patient
treatments and efficiency of the treatment planning process
while keeping dose ALARA
QA program should evolve and adapt as the device used for
CT simulation process change

References
Quality Assurance Programme for Computed Tomography; Diagnostic and
Therapy Application, International Atomic Energy Agency IAEA, Human Health
Series No. 19, 2012, ISBN 978–92–0–128910–0
Quality assurance workbook for radiographers & radiological technologists, World
Health Organization, 2001, ISBN 9241546425
American Association of Physicists in Medicine. Quality Assurance for Computed-
Tomography Simulators and the Computed Tomography- Simulation Process:
Report of the AAPM Radiation Therapy Committee Task Group No. 66.,2003.
Quality Control Recommendations for Diagnostic Radiography Conference of
Radiation Control Programme Directors Inc. CRCPD, Volume 2, 2001

References
American College of Radiology, Computed Tomography Quality Control Manual,
2012
Smith Steven W., The Scientist and Engineer’s Guide to Digital Signal Processing,
1997-1998
Phillip W. Ballinger, Eugene D. Frank, volume 3: Merrill's Atlas of Radiographic
Positions and Radiologic Procedures, Edition 10, ISBN (Set) 0-323-01604-9
Jerrold T. Bushberg, J. Anthony Seibert, Edwin M. Leidholdt Jr., John N. Boone,
The Essential Physic of Medical Imaging, second edition, ISBN 0-683-30118-7
Kak A.C., Slaney M., Principles of Computed Tomographic Imaging. SIAM, 1987.
Flohr T.G., Schaller S., Stierstorfer K., et al., "Multi-Detector Row CT Systems and
Image-Reconstruction Techniques," Radiology, June 2005.

The End ???..... I Don’t Think So!!!

Quality Assurance Programme in Computed Tomography

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