Computed Tomography Principles, Design, Artifacts, and Recent Advances

562 Pages·2009·126 MB·English

by  Jiang Hsieh

Bellingham, Washington USA
Library of Congress Cataloging-in-Publication Data

Hsieh, Jiang.
Computed tomography : principles, design, artifacts, and recent advances / Jiang Hsieh.
-- 2nd ed.
p. ; cm.
Includes bibliographical references and index.
ISBN 978-0-8194-7533-6
1. Tomography. I. SPIE (Society) II. Title.
[DNLM: 1. Tomography, X-Ray Computed. 2. Tomography Scanners, X-Ray
Computed--trends. 3. Tomography, X-Ray Computed--instrumentation. 4. Tomography,
X-Ray Computed--trends. WN 206 H873c 2009]
RC78.7.T6H757 2009
616.07'572--dc22
2009004797

Published by

SPIE
P.O. Box 10
Bellingham, Washington 98227-0010 USA
Phone: [phone]
Fax: [phone]
Email: [email protected]
Web: http://spie.org

and

John Wiley & Sons, Inc.
111 River Street
Hoboken, New Jersey 07030
Phone: [phone]
Fax: [phone]
ISBN: 9780470563533

Copyright © 2009 Society of Photo-Optical Instrumentation Engineers

All rights reserved. No part of this publication may be reproduced or distributed in any
form or by any means without written permission of the publisher.

The content of this book reflects the work and thought of the author(s).
Every effort has been made to publish reliable and accurate information herein, but the
publisher is not responsible for the validity of the information or for any outcomes
resulting from reliance thereon.

Printed in the United States of America.
Contents

Preface xi

Nomenclature and Abbreviations xiii

1 Introduction 1
1.1 Conventional X-ray Tomography 2
1.2 History of Computed Tomography 7
1.3 Different Generations of CT Scanners 14
1.4 Problems 19
References 19

2 Preliminaries 23
2.1 Mathematics Fundamentals 23
2.1.1 Fourier transform and convolution 23
2.1.2 Random variables 27
2.1.3 Linear algebra 30
2.2 Fundamentals of X-ray Physics 33
2.2.1 Production of x rays 33
2.2.2 Interaction of x rays with matter 36
2.3 Measurement of Line Integrals and Data Conditioning 42
2.4 Sampling Geometry and Sinogram 46
2.5 Problems 48
References 52

3 Image Reconstruction 55
3.1 Introduction 55
3.2 Several Approaches to Image Reconstruction 57
3.3 The Fourier Slice Theorem 61
3.4 The Filtered Backprojection Algorithm 65
3.4.1 Derivation of the filtered back-projection
formula 68
3.4.2 Computer implementation 71
3.4.3 Targeted reconstruction 85
3.5 Fan-Beam Reconstruction 88
3.5.1 Reconstruction formula for equiangular
sampling 89
v
vi Contents
3.5.2 Reconstruction formula for equal-spaced
sampling 95
3.5.3 Fan-beam to parallel-beam rebinning 97
3.6 Iterative Reconstruction 101
3.6.1 Mathematics verses reality 102
3.6.2 The general approach to iterative
reconstruction 103
3.6.3 Modeling of the scanner’s optics and physics 105
3.6.4 Updating strategy 109
3.7 Problems 112
References 114

4 Image Presentation 119
4.1 CT Image Display 119
4.2 Volume Visualization 123
4.2.1 Multiplanar reformation 123
4.2.2 MIP, minMIP, and volume rendering 128
4.2.3 Surface rendering 136
4.3 Impact of Visualization Tools 137
4.4 Problems 140
References 142

5 Key Performance Parameters of the CT Scanner 143
5.1 High-Contrast Spatial Resolution 143
5.1.1 In-plane resolution 144
5.1.2 Slice sensitivity profile 150
5.2 Low-Contrast Resolution 154
5.3 Temporal Resolution 160
5.4 CT Number Accuracy and Noise 167
5.5 Performance of the Scanogram 172
5.6 Problems 174
References 176

6 Major Components of the CT Scanner 179
6.1 System Overview 179
6.2 The X-ray Tube and High-Voltage Generator 180
6.3 The X-ray Detector and Data-Acquisition Electronics 190
6.4 The Gantry and Slip Ring 197
6.5 Collimation and Filtration 199
6.6 The Reconstruction Engine 202
6.7 Problems 203
References 205
Contents vii
7 Image Artifacts: Appearances, Causes, and Corrections 207
7.1 What Is an Image Artifact? 207
7.2 Different Appearances of Image Artifacts 209
7.3 Artifacts Related to System Design 214
7.3.1 Aliasing 214
7.3.2 Partial volume 226
7.3.3 Scatter 231
7.3.4 Noise-induced streaks 235
7.4 Artifacts Related to X-ray Tubes 239
7.4.1 Off-focal radiation 239
7.4.2 Tube arcing 242
7.4.3 Tube rotor wobble 244
7.5 Detector-induced Artifacts 244
7.5.1 Offset, gain, nonlinearity, and radiation
damage 244
7.5.2 Primary speed and afterglow 248
7.5.3 Detector response uniformity 253
7.6 Patient-induced Artifacts 258
7.6.1 Patient motion 258
7.6.2 Beam hardening 270
7.6.3 Metal artifacts 280
7.6.4 Incomplete projections 283
7.7 Operator-induced Artifacts 288
7.8 Problems 291
References 295

8 Computer Simulation and Analysis 301
8.1 What Is Computer Simulation? 301
8.2 Simulation Overview 303
8.3 Simulation of Optics 305
8.4 Computer Simulation of Physics-related Performance 316
8.5 Problems 323
References 324

9 Helical or Spiral CT 327
9.1 Introduction 327
9.1.1 Clinical needs 327
9.1.2 Enabling technology 331
9.2 Terminology and Reconstruction 332
9.2.1 Helical pitch 332
9.2.2 Basic reconstruction approaches 333
9.2.3 Selection of the interpolation algorithm and
reconstruction plane 339
9.2.4 Helical fan-to-parallel rebinning 343
9.3 Slice Sensitivity Profile and Noise 348
viii Contents
9.4 Helically Related Image Artifacts 355
9.4.1 High-pitch helical artifacts 355
9.4.2 Noise-induced artifacts 360
9.4.3 System-misalignment-induced artifacts 364
9.4.4 Helical artifacts caused by object slope 368
9.5 Problems 371
References 372

10 Multislice CT 375
10.1 The Need for Multislice CT 375
10.2 Detector Configurations of Multislice CT 378
10.3 Nonhelical Mode of Reconstruction 385
10.4 Multislice Helical Reconstruction 396
10.4.1 Selection of interpolation samples 398
10.4.2 Selection of region of reconstruction 402
10.4.3 Reconstruction algorithms with 3D
backprojection 405
10.5 Multislice Artifacts 410
10.5.1 General description 410
10.5.2 Multislice CT cone-beam effects 411
10.5.3 Interpolation-related image artifacts 413
10.5.4 Noise-induced multislice artifacts 416
10.5.5 Tilt artifacts in multislice helical CT 416
10.5.6 Distortion in step-and-shoot mode SSP 419
10.5.7 Artifacts due to geometric alignment 420
10.5.8 Comparison of multislice and single-slice
helical CT 422
10.6 Problems 422
References 425

11 X-ray Radiation and Dose-Reduction Techniques 433
11.1 Biological Effects of X-ray Radiation 434
11.2 Measurement of X-ray dose 436
11.2.1 Terminology and the measurement
standard 436
11.2.2 Other measurement units and methods 442
11.2.3 Issues with the current CTDI 443
11.3 Methodologies for Dose Reduction 445
11.3.1 Tube-current modulation 446
11.3.2 Umbra-penumbra and overbeam issues 448
11.3.3 Physiological gating 451
11.3.4 Organ-specific dose reduction 454
11.3.5 Protocol optimization and impact of the
operator 456
11.3.6 Postprocessing techniques 461
Contents ix
11.3.7 Advanced reconstruction 462
11.4 Problems 463
References 465

12 Advanced CT Applications 469
12.1 Introduction 469
12.2 Cardiac Imaging 471
12.2.1 Coronary artery calcification (CAC) 472
12.2.2 Coronary artery imaging (CAI) 476
12.2.2.1 Data acquisition and
reconstruction 478
12.2.2.2 Temporal resolution improvement 485
12.2.2.3 Spatial resolution improvement 492
12.2.2.4 Dose and coverage 493
12.3 CT Fluoroscopy 497
12.4 CT Perfusion 503
12.5 Screening and Quantitative CT 512
12.5.1 Lung cancer screening 512
12.5.2 Quantitative CT 516
12.5.3 CT colonography 519
12.6 Dual-Energy CT 522
12.7 Problems 532
References 534

Glossary 545

Index 551
Preface

Since the release of the first edition of this book in 2003, x-ray computed
tomography (CT) has experienced tremendous growth thanks to technological
advances and new clinical discoveries. Few could have predicted the speed and
magnitude of the progress, and even fewer could have predicted the diverse
nature of the technological advancement. The second edition of this book
attempts to capture these advances and reflect on their clinical impact.
The second edition provides significant changes and additions in several
areas. The first major addition is a new chapter on radiation dose. In the last few
years, significant attention has been paid to this subject by academic researchers,
radiologists, the general public, and the news media. An increased awareness of
the impact of radiation dose on human health has led to the gradual adoption of
the “as low as reasonably achievable” (ALARA) principle, the implementation of
American College of Radiology (ACR) accreditation and other dose reference
levels, and the development of many advanced dose-saving features for CT
scanners. The new Chapter 11 briefly describes some of the known biological
effects of radiation dose, then presents different dose definitions and
measurements, and concludes with an illustration of various dose-reduction
techniques.
At the time the first edition was published, the term “multislice” CT was an
accurate description of state-of-the-art scanners. Sixteen-slice scanners had just
been introduced commercially, and their clinical utilities and advantages had just
begun to be discovered. Since then, the “slice war” has continued, and now 64-,
128-, 256-, and 320-slice scanners are the new state of the art. These scanners
can be easily labeled as “cone-beam” CT. They require not only a detector with
wider coverage, but also other technologies such as new calibration techniques
and reconstruction algorithms. Chapter 10 has been significantly expanded to
discuss the technologies associated with these scanners and the new image
artifacts created by them.
Since the first edition, CT advancement has not been limited to the technology.
Advances also have been made in many areas of clinical applications, including the
rapid development of cardiac CT imaging and new applications inspired by the
reintroduction of dual-energy CT. Chapter 12 presents these advances and the
fundamental physics and technologies behind them.
Image artifacts have accompanied x-ray CT ever since its birth over 30 years
ago. Some artifacts are caused by the characteristics of the physics involved,
some are caused by technological limitations, some are created by new
xi