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Sixteen-Section Multi–Detector Row CT Scanners
Guest Editorial
Sixteen-Section Multi–Detector Row CT Scanners: This Changes Everything1 Reuben Mezrich, MD, PhD
I don’t think it is much of an exaggeration to say that the new generation of multi– detector row computed tomographic (CT) scanners—the 16-section scanners— changes everything. It’s not just that they are fast; although speed may be important for obtaining high-quality images of the chest or abdomen, it doesn’t add much quality in imaging of the brain or spine or other body parts that don’t move much. It’s not that they provide high resolution, because in fact the axial resolution is no better than that provided by even the single-section CT scanners introduced quite a few years ago. What makes these new scanners so different is that for the first time the image voxels are isotropic; the image resolution can be as good in the sagittal and coronal planes as it is in the axial plane. Unlike the situation with single-section or even four-section multi– detector row scanners, with 16-section scanners there is no preferred plane for image reconstruction. The fact that the images may have been acquired in the axial plane is irrelevant. All planes have equal resolution, and the viewer can choose the plane that best shows the anatomy. One of the advantages of magnetic resonance imaging over CT was that it was possible to acquire images in arbitrary planes, but that advantage was realized only when one knew, a priori, which plane would be best. With the new 16-section multi– detector row CT scanners, one can decide after the fact which plane is optimal—axial, sagittal, coronal, or oblique—and vary it at will. This means that CT studies are no longer a collection of axial sections to be viewed one section at a time, but now are three-dimen-
Acad Radiol 2003; 10:351–352 1 From the Department of Radiology, University of Maryland School of Medicine, 22 S Greene St, Baltimore, MD 21201. Received and accepted January 2, 2003. Address correspondence to the author.
©
AUR, 2003
sional volumes that can be manipulated and displayed in whatever fashion best suits the diagnostic problem. The fact that these scanners perform at high speed is an enormous bonus. Artifacts due to respiratory and peristaltic motion are reduced or eliminated, while cardiac synchronization becomes simpler and more accurate. These features open up entirely new applications for CT, perhaps the most important of which are in cardiology. With submillimeter isotropic resolution, it should be possible to detect critical lesions even in the distal portions of the coronary arteries. With fewer artifacts due to volume averaging, it might even be possible to see “vulnerable plaques” (cholesterol-filled lesions in the walls of the coronary and carotid arteries that are thought to be the cause of most heart attacks and strokes) (1–5). With the ability to synchronize cardiac motion and to reformat volumes in any plane for viewing from any angle, it will be easy to display cine loops of two-, three-, and four-chamber views showing ventricular wall motion and cardiac function in exquisite detail and with precise accuracy. It will be possible, in short, to achieve the holy grail of cardiac imaging—the one-stop cardiac study that could change the way acute or chronic heart disease is diagnosed and followed up. One can imagine, for example, CT scanning being the first and perhaps the only test performed on the patient presenting at the emergency room with chest pain. At one swoop, acute myocardial infarction, pulmonary embolus, aortic dissection, pneumothorax, or even pneumonia can be diagnosed or excluded in a matter of minutes and the patient either sent home or on to treatment, with full confidence that appropriate and cost-effective care has been given. Along with these opportunities come many challenges, some technical and some social. Acquisition of high-quality images will require an understanding of the technology and physics behind CT operation that extends well beyond what was necessary for operating prior genera-
351
MEZRICH
tions of CT equipment. The article by Flohr et al (6) in this issue of Academic Radiology provides much of the material needed for that understanding, in a very clear and intelligent manner. The determinants of image resolution and image contrast are explained. The differences between four-section and 16-section images are outlined, and the effectiveness of high-resolution imaging in minimizing the inaccuracies produced by volume averaging is well described. Methods for cardiac synchronization are explained and illustrated. This article is important reading for all who want to take full advantage of this new imaging technology. However, the resulting high-resolution images will be for naught if the tools to manipulate the data are not available or not properly used. It is physically impossible to review studies with thousands of sections if those studies are recorded on film; if a commitment to acquire and use sophisticated workstations has not been made, then it makes no sense to acquire a multi– detector row CT scanner. Furthermore, in my opinion, it is not enough to rely on a technologist to manipulate the images, even in a specialized central facility with advanced three-dimensional rendering capabilities. The person interpreting the data should be a radiologist who is familiar with, and experienced in using, the sophisticated three-dimensional workstation. A volume of data—which is what the new CT scanners create—is different from a collection of images. It is not something static to be reviewed but rather a dynamic thing to be manipulated and maneuvered to best show the information. This process is not unlike that described by Michelangelo, who said that the statues he sculpted were embedded in the block of unworked marble, and he just chipped away the exterior to reveal their structure. The radiologist working with this new CT technology will need two things: the tools to manipulate the data, and the will to learn how to use those tools. This last—the will to learn—is one of the important social challenges presented by the new technology. An equally important social challenge will occur in the interaction between radiologists and their clinical colleagues. A tool that can so dramatically change patient work-up obviously will affect how, or even whether, clinicians do their jobs. Some clinicians will applaud the
352
Academic Radiology, Vol 10, No 4, April 2003
benefits to patient care and react by referring more patients to radiologists. Others will appreciate the benefits of the new CT technology and will decide to learn to use it themselves. Who provides the new CT studies will be determined by the service and value added. It will not be enough for radiologists to describe the anatomy, because clinicians will be able to see it for themselves. The provider of radiologic services must be able to detect abnormality (or its absence), determine the nature of the finding, and suggest further tests or procedures that might benefit the patient. It will not be useful to fight for control by political means or to assume referrals will continue because they always have. It will be better to maintain control by virtue of the value added to the service. The providers of these new services must truly act as consultants to the referring physicians and as resources for the patients, not just as quality-control administrators. If the providers are to be radiologists, then radiologists must be willing to participate in patient care and to offer opinions that will affect patient care. Their participation must add value and be relevant. This will challenge some and encourage others. It will necessitate changes in how we educate our residents and ourselves. It will mean less isolation and more collaboration. It will mean moving radiologists from the back of the line in patient care to the front of the line. It must be so, because this new generation of machines changes everything. REFERENCES 1. Fayad ZA, Fuster V. Clinical imaging of the high-risk or vulnerable atherosclerotic plaque. Circ Res 2001; 89:305–316. 2. Taylor AJ. Atherosclerosis imaging to detect and monitor cardiovascular risk. Am J Cardiol 2002; 90:8L–11L. 3. McConnell MV. Imaging techniques to predict cardiovascular risk. Curr Cardiol Rep 2000; 2:300 –307. 4. Hatsukami TS, Ross R, Polissar NL, Yuan C. Visualization of fibrous cap thickness and rupture in human atherosclerotic carotid plaque in vivo with high-resolution magnetic resonance imaging. Circulation 2000; 102:959 –964. 5. Fayad ZA, Fuster V, Nikolaou K, Becker C. Computed tomography and magnetic resonance imaging for noninvasive coronary angiography and plaque imaging: current and potential future concepts. Circulation 2002; 106:2026 –2034. 6. Flohr TG, Schoepf UJ, Kuettner A, et al. Advances in cardiac multi-section CT imaging with 16-section CT systems. Acad Radiol 2003; 10: 386 – 401.
Sixteen-Section Multi–Detector Row CT Scanners: This Changes Everything1 Reuben Mezrich, MD, PhD
I don’t think it is much of an exaggeration to say that the new generation of multi– detector row computed tomographic (CT) scanners—the 16-section scanners— changes everything. It’s not just that they are fast; although speed may be important for obtaining high-quality images of the chest or abdomen, it doesn’t add much quality in imaging of the brain or spine or other body parts that don’t move much. It’s not that they provide high resolution, because in fact the axial resolution is no better than that provided by even the single-section CT scanners introduced quite a few years ago. What makes these new scanners so different is that for the first time the image voxels are isotropic; the image resolution can be as good in the sagittal and coronal planes as it is in the axial plane. Unlike the situation with single-section or even four-section multi– detector row scanners, with 16-section scanners there is no preferred plane for image reconstruction. The fact that the images may have been acquired in the axial plane is irrelevant. All planes have equal resolution, and the viewer can choose the plane that best shows the anatomy. One of the advantages of magnetic resonance imaging over CT was that it was possible to acquire images in arbitrary planes, but that advantage was realized only when one knew, a priori, which plane would be best. With the new 16-section multi– detector row CT scanners, one can decide after the fact which plane is optimal—axial, sagittal, coronal, or oblique—and vary it at will. This means that CT studies are no longer a collection of axial sections to be viewed one section at a time, but now are three-dimen-
Acad Radiol 2003; 10:351–352 1 From the Department of Radiology, University of Maryland School of Medicine, 22 S Greene St, Baltimore, MD 21201. Received and accepted January 2, 2003. Address correspondence to the author.
©
AUR, 2003
sional volumes that can be manipulated and displayed in whatever fashion best suits the diagnostic problem. The fact that these scanners perform at high speed is an enormous bonus. Artifacts due to respiratory and peristaltic motion are reduced or eliminated, while cardiac synchronization becomes simpler and more accurate. These features open up entirely new applications for CT, perhaps the most important of which are in cardiology. With submillimeter isotropic resolution, it should be possible to detect critical lesions even in the distal portions of the coronary arteries. With fewer artifacts due to volume averaging, it might even be possible to see “vulnerable plaques” (cholesterol-filled lesions in the walls of the coronary and carotid arteries that are thought to be the cause of most heart attacks and strokes) (1–5). With the ability to synchronize cardiac motion and to reformat volumes in any plane for viewing from any angle, it will be easy to display cine loops of two-, three-, and four-chamber views showing ventricular wall motion and cardiac function in exquisite detail and with precise accuracy. It will be possible, in short, to achieve the holy grail of cardiac imaging—the one-stop cardiac study that could change the way acute or chronic heart disease is diagnosed and followed up. One can imagine, for example, CT scanning being the first and perhaps the only test performed on the patient presenting at the emergency room with chest pain. At one swoop, acute myocardial infarction, pulmonary embolus, aortic dissection, pneumothorax, or even pneumonia can be diagnosed or excluded in a matter of minutes and the patient either sent home or on to treatment, with full confidence that appropriate and cost-effective care has been given. Along with these opportunities come many challenges, some technical and some social. Acquisition of high-quality images will require an understanding of the technology and physics behind CT operation that extends well beyond what was necessary for operating prior genera-
351
MEZRICH
tions of CT equipment. The article by Flohr et al (6) in this issue of Academic Radiology provides much of the material needed for that understanding, in a very clear and intelligent manner. The determinants of image resolution and image contrast are explained. The differences between four-section and 16-section images are outlined, and the effectiveness of high-resolution imaging in minimizing the inaccuracies produced by volume averaging is well described. Methods for cardiac synchronization are explained and illustrated. This article is important reading for all who want to take full advantage of this new imaging technology. However, the resulting high-resolution images will be for naught if the tools to manipulate the data are not available or not properly used. It is physically impossible to review studies with thousands of sections if those studies are recorded on film; if a commitment to acquire and use sophisticated workstations has not been made, then it makes no sense to acquire a multi– detector row CT scanner. Furthermore, in my opinion, it is not enough to rely on a technologist to manipulate the images, even in a specialized central facility with advanced three-dimensional rendering capabilities. The person interpreting the data should be a radiologist who is familiar with, and experienced in using, the sophisticated three-dimensional workstation. A volume of data—which is what the new CT scanners create—is different from a collection of images. It is not something static to be reviewed but rather a dynamic thing to be manipulated and maneuvered to best show the information. This process is not unlike that described by Michelangelo, who said that the statues he sculpted were embedded in the block of unworked marble, and he just chipped away the exterior to reveal their structure. The radiologist working with this new CT technology will need two things: the tools to manipulate the data, and the will to learn how to use those tools. This last—the will to learn—is one of the important social challenges presented by the new technology. An equally important social challenge will occur in the interaction between radiologists and their clinical colleagues. A tool that can so dramatically change patient work-up obviously will affect how, or even whether, clinicians do their jobs. Some clinicians will applaud the
352
Academic Radiology, Vol 10, No 4, April 2003
benefits to patient care and react by referring more patients to radiologists. Others will appreciate the benefits of the new CT technology and will decide to learn to use it themselves. Who provides the new CT studies will be determined by the service and value added. It will not be enough for radiologists to describe the anatomy, because clinicians will be able to see it for themselves. The provider of radiologic services must be able to detect abnormality (or its absence), determine the nature of the finding, and suggest further tests or procedures that might benefit the patient. It will not be useful to fight for control by political means or to assume referrals will continue because they always have. It will be better to maintain control by virtue of the value added to the service. The providers of these new services must truly act as consultants to the referring physicians and as resources for the patients, not just as quality-control administrators. If the providers are to be radiologists, then radiologists must be willing to participate in patient care and to offer opinions that will affect patient care. Their participation must add value and be relevant. This will challenge some and encourage others. It will necessitate changes in how we educate our residents and ourselves. It will mean less isolation and more collaboration. It will mean moving radiologists from the back of the line in patient care to the front of the line. It must be so, because this new generation of machines changes everything. REFERENCES 1. Fayad ZA, Fuster V. Clinical imaging of the high-risk or vulnerable atherosclerotic plaque. Circ Res 2001; 89:305–316. 2. Taylor AJ. Atherosclerosis imaging to detect and monitor cardiovascular risk. Am J Cardiol 2002; 90:8L–11L. 3. McConnell MV. Imaging techniques to predict cardiovascular risk. Curr Cardiol Rep 2000; 2:300 –307. 4. Hatsukami TS, Ross R, Polissar NL, Yuan C. Visualization of fibrous cap thickness and rupture in human atherosclerotic carotid plaque in vivo with high-resolution magnetic resonance imaging. Circulation 2000; 102:959 –964. 5. Fayad ZA, Fuster V, Nikolaou K, Becker C. Computed tomography and magnetic resonance imaging for noninvasive coronary angiography and plaque imaging: current and potential future concepts. Circulation 2002; 106:2026 –2034. 6. Flohr TG, Schoepf UJ, Kuettner A, et al. Advances in cardiac multi-section CT imaging with 16-section CT systems. Acad Radiol 2003; 10: 386 – 401.