MDCT and 3D Workstations

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3 MDCT and 3D Workstations

4 Scott A. Lipson, MD Associate Director of Imaging, Long Beach Memorial Medical Center, Long Beach, California MDCT and 3D Workstations A Practical How-To Guide and Teaching File With 101 Figures in 379 Parts, 175 in Full Color

5 Scott A. Lipson, MD Associate Director of Imaging Long Beach Memorial Medical Center Long Beach, CA Library of Congress Control Number: ISBN 10: ISBN 13: Printed on acid-free paper Springer Science+Business Media, Inc. All rights reserved. This work may not be translated or copied in whole or in part without the written permission of the publisher (Springer Science+Business Media, Inc., 233 Spring Street, New York, NY 10013, USA), except for brief excerpts in connection with reviews or scholarly analysis. Use in connection with any form of information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed is forbidden. The use in this publication of trade names, trademarks, service marks, and similar terms, even if they are not identified as such, is not to be taken as an expression of opinion as to whether or not they are subject to proprietary rights. While the advice and information in this book are believed to be true and accurate at the date of going to press, neither the authors nor the editors nor the publisher can accept any legal responsibility for any errors or omissions that may be made. The publisher makes no warranty, express or implied, with respect to the material contained herein. Printed in China. (BS/EVB) springeronline.com

6 To Nancy and Shelly and the memory of my father, Sheldon, who has been a constant source of inspiration throughout my life

7 Preface Multidetector CT (MDCT) is much more than an incremental improvement over the previous technology. When compared with computed tomography (CT) imaging performed just 4 or 5 years ago, it is essentially a new modality. MDCT has significantly changed how I practice radiology and has reinvigorated my love for imaging. The images produced are not only clinically diagnostic, but they have an aesthetic beauty that is both accessible and enticing to radiologists, clinicians, and even patients. The purpose of writing this book is twofold. The first section brings together into one source all the practical information needed to successfully set up a MDCT practice, operate the scanners and 3D workstations, manage workflow, and consistently produce high-quality diagnostic images. The second section is a teaching file of volumetric cases. This is not intended to be a comprehensive collection of teaching material, but rather a showcase for the varied capabilities of current scanners and workstations. Each case is selected to demonstrate how the technology can improve the process of making a clinical diagnosis and then effectively relaying this information to other physicians in a format that is easy to understand. I hope that readers of this book will not only get a better understanding of MDCT and 3D workstations, but also a better appreciation of the art of radiology expressed by the images. Scott A. Lipson, MD vii

8 Acknowledgments I owe a debt of gratitude to Chris Gordon and her team of excellent CT technologists at Long Beach Memorial Medical Center. Without their hard work, dedication, and friendship, this book would not have been possible. I want to acknowledge the invaluable contribution of Dr. John Renner, the director of radiology at Long Beach Memorial. It was his vision that enabled Long Beach Memorial to be one of the very first hospitals in the United States to own and operate a 16-detector multidetector CT (MDCT). I also thank the administration at Long Beach, particularly Richard Decarlo and Terry Ashby for their support of this project. I am also indebted to my friends and collaborators from Toshiba America Medical Systems: Mike MacLeod, Bryan Westerman, Doug Ryan, and Jeff Hall, and from Vital Images, Vikas Narula. They have assisted and supported me over the years and have all contributed their expertise to this book in different ways. Finally, I would like to thank the following radiologists who contributed images or case discussions used in this book: Dr. Ruben Sebben, Dr. Hirofumi Anno, Dr. Albert de Roos, Dr. Stanley Laucks, Jr., and Dr. Alisa Watanabe. ix

9 Contents Preface Acknowledgments vii ix Part I How-to Guide to MDCT and 3D Workstations Chapter 1 Introduction Chapter 2 MDCT Data Acquisition Chapter 3 Delivery of Contrast Media for MDCT Chapter 4 Image Reconstruction and Review Chapter 5 3D Workstations: Basic Principles and Pitfalls Chapter 6 Guide to Clinical Workstation Use Chapter 7 Efficient CT Workflow Part II Volumetric Imaging Teaching File Chapter 8 Vascular Imaging Chapter 9 Pediatric Imaging Chapter 10 Trauma Imaging Chapter 11 Body Imaging xi

10 xii Contents Chapter 12 Cardiac Imaging Chapter 13 Orthopedic Imaging Chapter 14 Neuroimaging Appendix Sample CT Protocols Index

11 Part I How-to Guide to MDCT and 3D Workstations

12 Chapter 1 Introduction Just a few years ago three-dimensional (3D) imaging with computed tomography (CT) was a tool used primarily at a few select academic centers, often by specially trained technologists working in a dedicated 3D imaging lab. This situation has changed rapidly, however, and with the proliferation of multidetector CT (MDCT) scanners and advanced workstations, CT angiography (CTA) and volumetric imaging are now routine practice in community hospitals and imaging centers all over the world. This transition has been extremely rapid and for many radiologists quite difficult. Advances in CT and workstation technology have moved much faster than physician training and education. The equipment needed to perform volumetric imaging is straightforward. An MDCT scanner is essential, as is a 3D workstation. The images and cases that are used in this article were primarily acquired on a 16-slice MDCT (Aquilion 16, Toshiba Medical Systems, Japan), but the concepts and principles are applicable with minor modifications to 4-slice MDCT, as well as to the new generation of 32-, 40-, and 64-slice scanners. Acquiring the proper hardware is essential, but it is just the first step in the process. With the new equipment must also come a new philosophic approach to CT imaging. Volumetric imaging requires a paradigm shift in how radiologists acquire and review CT data. It is easy with MDCT to become overwhelmed by the amount of information that is available. Data sets now routinely number from several hundred to thousands of images. A coordinated and thoughtful approach is needed to handle this information. The goal is to provide higher quality imaging and to translate this into more accurate radiologic diagnosis and better patient care than ever before. The dilemma is how to accomplish all this without sacrificing work efficiency. To achieve these goals, radiologists must adapt how they review and think about CT data. Axial CT images remain important, but they are just one tool among many for case review. As radiologists become more comfortable with volumetric data, they rely less on any one imaging plane or reconstruction algorithm. Radiologists can choose the most appropriate imaging plane or planes for a given examination to review 3

13 4 Part I: How-to Guide to MDCT and 3D Workstations the data. Advanced picture archives and communication systems (PACS) and 3D workstations allow for volumetric image review that seamlessly integrates multiplanar data with the capability for volume rendered reconstructions and other advanced tools. The concept of slices becomes outdated. Volumetric data sets affect not only how we review the data but the type of examinations we perform with CT and how we scan the patients. The most dramatic impact is in the area of CTA. CT angiography is rapidly replacing diagnostic catheter angiography throughout the body (and perhaps soon even in the heart). The purely diagnostic catheter angiogram may soon become a rarity, gone the way of the exploratory laparotomy. Performing and processing CTA images has become dramatically easier as workstation technology has improved. Done correctly, it is an extremely powerful and accurate tool for evaluating the vascular tree. Many of those who use CTA routinely believe that in many cases it is truly the gold standard, replacing the catheter angiogram. Having said that, I must also admit that CTA is often not as easy as it looks. It requires careful attention to detail and a full knowledge of the strengths and weakness of different reconstruction techniques. Many significant pitfalls can lead an inexperienced user to make clinically important errors. The benefits of volumetric imaging are not limited to CTA, however. Every facet of CT imaging can be improved dramatically. For example, for musculoskeletal imaging, volumetric data sets from a single acquisition can be reconstructed in any conventional or oblique plane with no loss of resolution. Patient positioning is no longer of major importance, and the need to obtain direct coronal or sagittal scans no longer exists. Simple surface rendering techniques coupled with basic segmentation can provide a tremendous amount of information very quickly. For trauma patients, this has been an amazing revolution. With a single data acquisition, multiple examinations can be rapidly generated and interpreted. The goal of this book is to help guide radiologists, students, and technologists through the often complex and difficult areas of CT data acquisition, protocols, image reconstruction and review, and efficient workflow. Descriptions of how to effectively use 3D workstations to interpret and process images are also given, and practical examples for different types of cases are provided. The teaching file is designed to show interesting cases that illustrate how the technology can be used on a daily basis to improve diagnosis, patient care, and communication among radiologists, referring doctors, and patients.

14 Chapter 2 MDCT Data Acquisition Volumetric imaging requires routine acquisition of high-resolution data sets. The principles apply not just to cases such as CTA, but can be used for virtually every study performed. One major difference between single-slice CT and MDCT is a fundamental separation between how data are acquired and how they are reviewed. With single-slice CT there is frequently little difference between the slice thickness images are acquired at and the thickness in which they are reviewed. Volumetric MDCT depends on acquiring very thin section data sets that are used to generate thicker axial slices as well as multiplanar and volume images. Review of the very thin section axial images is less efficient and usually unnecessary, but the information remains available for those instances where it is needed. The goal of volumetric imaging with MDCT should be to acquire data sets with isotropic (or near-isotropic) voxels whenever possible. An isotropic voxel is a cube, measuring the same in the x, y, and z planes. A typical single-slice voxel has a dimension much longer in the z-axis than the x- or y-axis. This leads to adequate resolution in the plane of acquisition (usually axial) but poor-quality images for multiplanar reconstructions (MPRs) and 3D reconstructions. Isotropic voxels allow for true 3D imaging. No matter how the data set is projected, there is no significant loss in resolution. The size of the field of view (FOV) affects voxel size and, therefore, spatial resolution. With a standard CT imaging matrix of pixels and a FOV of 25cm, the pixel size in the x and y dimensions is approximately 0.5mm (Figure 2.1). Therefore, to achieve an isotropic voxel the z-axis resolution would need to be 0.5mm also. With a larger FOV such as 50cm, the in-plane pixel size increases to 1.0mm and an isotropic voxel would only require 1-mm slice thickness. This fact can be incorporated into protocol design. The FOV chosen should always be as small as possible to accommodate the anatomy of interest. Corresponding slice thickness should also be used to maximize resolution, given limitations in anatomic coverage needed or scan duration. 5

15 6 Part I: How-to Guide to MDCT and 3D Workstations Figure 2.1. Isotropic voxels at two different fields of view (FOV). With a large FOV (50cm) and a matrix, isotropic voxels are achieved with 1-mm slice thickness. With a smaller FOV (25 cm), 0.5-mm slice thickness is needed to achieve isotropic voxels. MDCT Scan Protocols Multidetector CT scanners offer a dizzying number of protocol options. Some of the major scan acquisition variables that the user must consider include scan mode (sequence vs. helical), slice number and thickness, helical pitch, FOV, rotation time, radiation dose parameters, and coverage needed (scan length). Once the data have been acquired, there are an equally large number of variables to consider in how the data are reconstructed and presented for viewing. These variables, such as reconstruction thickness and algorithm, and multiplanar reconstructions, are discussed separately. It is important to remember with MDCT that there is a fundamental difference in how the images are acquired and how they are viewed.