SPECIFICATION AND ACCEPTANCE TESTING OF …

AAPM REPORT NO. 39

SPECIFICATION AND ACCEPTANCE TESTING OF COMPUTED

TOMOGRAPHY SCANNERS

Published for the

American Association of Physicists in Medicine

i

by the American Institute of Physics

AAPM REPORT NO. 39

SPECIFICATION AND ACCEPTANCE TESTING OF COMPUTED TOMOGRAPHY SCANNERS

Report of Task Group 2 Diagnostic X-Ray Imaging Committee

AAPM Members Pei-Jan Paul Lin (Task Group Co-Chairman) Thomas J. Beck (Task Group Co-Chairman)

Caridad Borras Gerald Cohen Robert A. Jucius Robert J. Kriz Edward L. Nickoloff Lawrence N. Rothenberg Keith J. Strauss Theodore Villafana

Additional Contributors Robert K. Cacak Joel E. Gray

Thomas N. Hangartner R. Edward Hendrick Raymond P. Rossi

May 1993

Published for the American Association of Physicists in Medicine

by the American Institute of Physics

DISCLAIMER: This publication is based on sources and information believed to be reliable, but the AAPM and the editors disclaim any warranty or liability based on or relating to the contents of this publication.

The AAPM does not endorse any products, manufacturers or suppliers. Nothing in this publication should be interpreted as implying such endorsement.

Further copies of this report may be obtained from: American Association of Physicists in Medicine 335 East 45th Street New York, NY 10017

International Standard Book Number: 1-56396-230-6 International Standard Serial Number: 0271-7344

?1993 by the American Association of Physicists in Medicine

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means (electronic, mechanical, photocopying, recording, or otherwise) without the prior written permission of the publisher.

Published by the American Institute of Physics, Inc. 335 East 45th Street, New York, NY 10017

Printed in the United States of America

Preface

The Computed Tomography (CT) Scanner Task Group was formed to provide a reference document of suggested procedures for acceptance testing of CT systems for clinical medical physicists. The AAPM first addressed performance testing of CT systems with the publication of AAPM Report No. 1, "Phantoms for Performance Evaluation and Quality Assurance of CT Scanners". Since publication of Report No. 1 in 1977, CT system designs have evolved and research has improved our understanding of principles and limitations of CT systems. These changes in technology and our understanding of them prompted the formation of this task group.

This report is intended to be a source of acceptance testing procedures, as well as an educational tool for those medical physicists whose primary responsibilities lie in areas other than diagnostic imaging. In addition to acceptance testing procedures, the related issues of specification writing and radiation shielding design are also discussed.

Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .iii I.Introduction.................................................................1

A. THE BID REQUEST . . . . . . . . . . . . . . . . . . ........................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 B. EVALUATINGNEEDSOFTHEUSER........................................................................................2 C. EQUIPMENT SELECTION...............................................................................................................3 D. SPECIFICATION WRITING ..................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 II. Shielding Design........................................................................................4 III. Performance Evaluation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9

A. PERFORMANCE OF ELECTROMECHANICAL COMPONENTS ....................... . . . . . . . . . . . . . . .13 1. Scan Localization Light Accuracy ............................. ..14 2. Alignment of Table to Gantry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 3. Table/Gantry Tilt .................. . . . . . . . . . . . . .15 4. Slice Localization From Radiographic (Scout) Image . . . . . . .17 5. Table Incrementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...18 6. Collimation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 a. Radiation Profile Width . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 b. Sensitivity Profile Width................................................................20 7. The X-ray Generator..............................................................23

B. IMAGE QUALITY.......................................................................................26 1. Random Uncertainties in Pixel Value...........................................26 2 . Systematic Uncertainties in Pixel Value . . . . . . . . . . . . . . . . . . . . . . ..3 1 a. Image Artifacts . . . . . . . . . . . . . . . . . . .34 1) Geometric Artifacts.......................................................34 a) Aliasing.................................................................34 b) Edge Gradient Streaks .............................................34 c) Geometric Misalignment....................................................35 d) Motion Artifacts......................................................35 2) Reconstruction Algorithm Effects ..........................................35 a) Point Spread Effect..................................................35 b) Edge Enhancement Artifacts . . . . . . . . . . . . . . . . . . . . . . 35 3) Attenuation Measurement Errors . . . . . . . . . . . . . . . . . . . . . . 36 a) Detector or Source Variations . . . . . . . . . . . . . . . . . . . . 36 b) Nonlinear Attenuation Errors . . . . . . . . . . . . . . . . . . . . . 36 b. Measurement of Systematic Pixel Error . . . . . . . . . . . . . . . . . . . 37 1) Field Uniformity........................................................ 37 2) Considerations in Quantitative CT................................ .........39 3. Spatial Frequency Limits...........................................................41 a. High Contrast Spatial Frequency Limits . . . . . . . . . . . . . . . . . .41 1) Measuring Resolution With A Resolution Pattern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 2) Modulation Transfer Function Measurement.......44

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