Digital Radiography. Selected Topics

Digital Radiography Selected Topics

DIGITAL RADIOGRAPHY Selected Topics Editorial Advisory Board: PETER R. ALMOND, Ph.D. University of Louisville School of Medicine Louisville, Kentucky JOHN S. CLIFTON, M.Sc. Department of Medical Physics University College Hospital London, England J. F. FOWLER, Ph.D. Director, Gray Laboratory Mount Vernon Hospital Northwood, Middlesex, England JAMES G. KEREIAKES, Ph.D. Department of Radiology University of Cincinnati College of Medicine Cincinnati, Ohio JACK S. KROHMER, Ph.D. Georgetown, Texas CHRISTOPHER H. MARSHALL, Ph.D. N.Y.U. Medical Center New York, New York COLIN G. ORTON, Ph.D. Department of Radiation Oncology Wayne State University School of Medicine Harper-Grace Hospitals Detroit, Michigan

Digital Radiography Selected Topics Edited by James G. Kereiakes Stephen R. Thomas University of Cincinnati Col/ege of Medicine Cincinnati, Ohio and Colin G. Orton Wayne State University School of Medicine Harper-Grace Hospitals Detroit, Michigan Plenum Press New York and London

Digital radiography. Library of Congress Cataloging in Publication Data Includes bibliographies and index. 1. Radiography, Medical-Digital techniques. 2. Diagnostic imaging - Data processing. 3. Image processing-digital techniques. I. Kereiakes, James G., 1924-. II. Thomas, Stephen R. III. Orton, Colin G. [DNLM: 1. Radiology-instrumentation. 2. Radiography-methods. WN 200 D5745) RC78.7.D35D54 1986 616.07'57 86-3259 ISBN-13: 978-1-4684-5070-5 001: 1 0.1007/978-1-4684-5068-2 e-isbn-13: 978-1-4684-5068-2 1986 Plenum Press, New York A Division of Plenum Publishing Corporation 233 Spring Street, New York, N.Y. 10013 Softcover reprint of the hardcover 1 st edition 1986 All rights reserved No part of this book may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, microfilming, recording, or otherwise, without written permission from the Publisher

To our wives Helen, Ingrid, and Barbara for their continuing support and encouragement

Contributors R. E. Alvarez DigiRad Corporation, Palo Alto, California 94303 B. A. Arnold Image Analysis, Inc., Irvine, California 92714, and Department of Radiological Sciences, UCLA Medical School, Los Angeles, California 90024 R. Brennecke Medical Clinic, Johannes Gutenberg University, D-6500 Mainz, Federal Republic of Germany w. L. Henry Department of Medicine (Cardiology), University of California, Irvine, California 92716 J. G. Kereiakes Department of Radiology, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267 R. A. Kruger Department of Radiology, University of Utah College of Medicine, Salt Lake City, Utah 84132 A. V. Lando Department of Radiological Sciences, University of California, Irvine, California 92716 L. A. Lehmann DigiRad Corporation, Palo Alto, California 94303 O. Nalcioglu Department of Radiological Sciences, University of California, Irvine, California 92716 S. J. Riederer Department of Radiology, Duke University Medical Center, Durham, North Carolina 27710 W. W. Roeck Department of Radiological Sciences, University of California, Irvine, California 92716 J. A. Seibert Department of Radiology, University of California, Davis, California 95817 vii

viii CONTRIBUTORS s. R. Thomas Department of Radiology, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267 J. M. Tobis Department of Medicine (Cardiology), University of California, Irvine, California 92716

Preface Digital radiography is a general term describing any projection radiological system in which the image exists in digital form at some stage between acquisition and viewing. In an earlier form, radiographic films were digitized in an attempt to enhance and redisplay information of interest. The field has evolved to its current state, in which X-ray signals are detected electronically, converted to digital form, and processed prior to being recorded and displayed. A primary goal of digital radiography is the removal of interfering effects from secondary structures in an image, so that clinically significant details can be displayed with enhanced visibility. The achievement of this goal involves many parameters, including contrast agents, subtraction techniques, processing techniques, filtering techniques, system noise, and quantitative aspects. It is the purpose of this book to present material by noted individuals in the field covering several of the above topics. The authors acknowledge the secretarial and editorial assistance of Mrs. Helen Taylor and the editorial assistance of Mrs. Ruth McDevitt. James G. Kereiakes Stephen R. Thomas Cincinnati, Ohio Colin G. Orton Detroit, Michigan ix

Contents 1. DIGITAL RADIOGRAPHY: OVERVIEW B. A. Arnold, 1. G. Kereiakes, and S. R. Thomas 1. Introduction......... 2. Point-Scanned Detector Systems 3. Line-Scanned Detector Systems 4. Area Detector Systems 4.1. Stimulable Phosphors 4.2. Selenium Detectors. 4.3. Digital Video Systems 5. Comparison of X-Ray Imaging Systems 6. Summary References.... 1 3 4 5 5 6 7 8 10 10 2. IMAGE PROCESSORS FOR DIGITAL ANGIOGRAPHY: ALGORITHMS AND ARCHITECTURES R. Brennecke 1. Introduction...................... 13 2. Algorithms for Handling and Processing of Digitized Angiograms 14 2.1. Image Data Compression... 14 2.2. Image Enhancement by Digital Subtraction..... 15 2.3. Image Enhancement and Extraction by Digital Filtering of Pixeldensograms. 16 2.4. Image Analysis 17 2.5. Algorithm Structures. 17 2.5.1. Point Operations 17 2.5.2. Filtering of Pixeldensograms 17 2.5.3. Two-Dimensional Processing 18 2.6. Data Structure......... 18 3. Processor Architectures for Digital Angiography 20 3.1. General-Purpose Computer with Video Interface 20 3.2. Special-Purpose Processors for Real-Time Subtraction 21 xi

xii 3.3. Special Computer Systems for Digital Angiography 3.4. Experimental Systems for Digital Angiography 4. Conclusions and Discussion References.... CONTENTS 23 27 30 31 3. TEMPORAL INTEGRATION PROCESSING TECHNIQUES s. 1. Riederer 1. Introduction........... 2. Theory.... 2.1. The Conventional DSA Reference 2.2. Temporal Integration 2.3. Matched Filtering 3. Implementation 4. Applications..... 4.1. SNR Improvement 4.2. X-Ray Exposure Reduction. 4.3. Contrast Dose Reduction 4.4. Hybrid Subtraction SNR Recovery 5. Discussion References.... 35 36 36 36 37 41 44 44 46 49 51 52 53 4. NOISE ANAL YSIS IN DIGITAL RADIOGRAPHY B. A. Arnold 1. Introduction. 2. Sources of Noise in Digital Systems 3. Conspicuity and Image Subtraction 4. Theoretical Analysis.... 4.1. Detail SNR........ 4.2. Detectability Threshold and Image Gray Levels 4.3. Contrast-Detail Relationship for Threshold Detectability 4.4. Detector Quantum Efficiency...... 4.5. Minimum Patient Exposure for Detection. 4.6. Sample Calculations for Digital Angiography 4.7. Summary of Theoretical Analysis 5. Experimental Measurements of Noise 5.1. SNR.... 5.2. Scattered Radiation and Detail SNR 5.3. Wiener Power Spectra...... 5.4. Phantom Tests of Iodine Detectability 6. Summary References.... 55 57 61 63 63 65 66 67 67 68 71 71 71 74 75 78 80 80

CONTENTS xiii 5. QUANTITATIVE ASPECTS OF IMAGE INTENSIFIER-TELEVISION-BASED DIGITAL X-RA Y IMAGING O. Nalcioglu, W. W. Roeck, 1. A. Seibert, A. V. Lando, 1. M. Tobis, and W. L. Henry 1. Introduction......... 2. System Description...... 2. J. X-Ray Generator and Tube. 2.2. Object..... 2.3. Image Intensifier..... 2.4. Television Camera.... 2.5. Analog-to-Digital Converter 2.6. Image Acquisition Memory. 2.7. Measurement of System Response 2.7.1. TV Camera Response 2.7.2. II-TV Response... 2.8. System Spatial Resolution... 3. Characterization of Physical Degradation Factors 3. J. Beam Hardening 3.2. X-Ray Scatter............ 3.3. Veiling Glare............ 4. Effect of Degradation Factors on Videodensitometric Volume Measurements...... 4.1. Absolute Volume Measurements... 4.2. Relative Volume Measurements. 5. Techniques for Reduction of Degradation Factors. 5. J. Veiling Glare............. 5.1.1. Deconvolution of Lead Disk Images 5.1.2. Effects of Glare Deconvolution on Volume Measurements 5.2. X-Ray Scatter. 5.3. Beam Hardening.. 6. Applications...... 6.1. Relative Volume Measurements 6.1.1. Measurement of Ventricular Ejection Fraction 6.1.2. Stenosis Measurement.. 6.2. Absolute Volume Measurements 7. Summary References 83 84 85 86 86 87 88 90 90 90 91 92 92 93 95 98 100 102 106 107 107 III 113 114 117 120 121 122 124 126 130 131 6. RECURSIVE FILTERING TECHNIQUES APPLIED TO DIGITAL SUBTRACTION ANGIOGRAPHY R. A. Kruger 1. Introduction...... 2. Temporal Filtering Theory 133 134

xiv 3. Noncardiac Clinical Results Using Recursive Filtering 4. Cardiac Applications References.... CONTENTS 139 140 142 7. ENERGY-SELECTIVE RADIOGRAPHY: A REVIEW L. A. Lehmann and R. E. Alvarez 1. Introduction........... 145 2. Apparatus for Energy-Selective Imaging 147 3. Decomposition of the Attenuation Coefficient 151 3.1. Intuitive Limits to Dimensionality... 153 3.2. The Singular Value Decomposition... 154 4. Conditions for Calculating Complete Energy-Dependent Information 157 4.1. Vector Space Descriptions of Mixtures and Line Integrals 157 4.2. Calculation of Line Integrals in Conventional Radiographic Systems............... 158 4.3. Complete Information Extraction in Energy-Selective Systems. 159 5. Applications of Energy-Selective Imaging 162 5.1. Synthesized Monoenergetic Images 162 5.2. Selective Material Images.... 163 5.3. Generalized Projection Signal Processing 168 5.4. Computation for Energy-Selective Imaging 169 6. Analysis of Conspicuity and Noise...... 173 6.1. Statistics of Basis Coefficient Estimation 173 6.2. Basis Noise and the System's Physical Properties. 176 6.3. Noise Optimal Generalized Projections. 177 6.4. Comparison of Noise in Conventional and Energy-Selective Systems 181 6.5. Conspicuity Enhancement 183 7. Conclusion 186 References... 187 INDEX........................... 189