EDITORIAL COMMENT
Integrating Multidetector Computed Tomography Into Clinical PracticeComputed Tomography Scanning Shows its Metal*
Basil S. Lewis, MD, FRCP, FACC* and
David A. Halon, MB ChB, FACC
Department of Cardiovascular Medicine, Lady Davis Carmel Medical Center, and the Ruth and Bruce Rappaport School of Medicine, Technion-Israel Institute of Technology, Haifa, Israel.
* Reprint requests and correspondence: Dr. Basil S. Lewis, Department of Cardiovascular Medicine, The Heart Hospital at Lady Davis Carmel Medical Center, 7 Michal Street, Haifa 34362, Israel. (Email: lewis{at}tx.technion.ac.il).
Selective coronary angiography (1) opened the era of in vivo visualization of the coronary arteries. It allowed new insights into the pathophysiology of coronary syndromes and made it possible to perform myocardial revascularization using bypass surgery and percutaneous coronary intervention (PCI). Almost 50 years later, advances in technology have opened another new era, this time an era of noninvasive cardiac imaging. Specifically, multidetector computed tomography (MDCT) is capable of providing high-quality almost-instant noninvasive coronary angiography, with high diagnostic accuracy for the assessment of coronary stenoses (2–10) and the identification and characterization of coronary plaques (11,12).
Until recently, MDCT has been of limited value in the assessment and follow-up of the revascularized patient. In the post-PCI patient, blooming artifact from the metallic stent produces a "napkin-ring appearance" on MDCT (Fig. 1) and may obscure some 30% of the stent luminal dimension, making the diagnosis of in-stent restenosis quite difficult (13). Indeed, stented segments—the most important part of the coronary tree requiring assessment in the post-PCI patient—were simply omitted in most reports validating the cardiac use of MDCT. In the post-bypass patient, a relatively large volume of contrast medium and longer breath hold time are necessary to image the area from clavicle to diaphragm and to include the origin of internal mammary arteries as well as proximal and distal graft anastomoses and distal native segments. The blooming artifact introduced by metal clips may again prevent accurate definition of graft segments, whereas beam hardening can produce dark areas adjacent to clips that may simulate stenoses, especially at points of anastomosis. In both the bypass patient and the stent patient, native vessel calcification may be extensive, thus further reducing diagnostic accuracy.
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Figure 1 Three-Dimensional Volume Rendering Reconstruction
Reconstruction (A) of the left anterior descending (LAD) and circumflex (Cx) coronary arteries. The stent (arrow) has a napkin ring appearance because of the blooming artifact produced by the metal struts. (B) The 2-dimensional reconstruction (long and short axis, inset) shows a blooming artifact, which complicates the diagnosis of in-stent restenosis.
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New-generation MDCT scanners have allowed us to begin to examine patients with implanted coronary stents (14) and to assess patients with coronary bypass grafts (15). In this issue of the Journal, 2 papers describe the role of 64-slice MDCT scanning in revascularized patients. Ehara et al. (16) report the use of MDCT for diagnosing in-stent restenosis. Using 2 dataset reconstructions based on a soft and a sharp image formulation, the investigators produced high-definition images of stents and of contrast-poor regions at sites of intimal proliferation partially obscuring the arterial lumen. Sensitivity, specificity, positive predictive values (PPV) and negative predictive values (NPV) for assessable stents (compared with invasive angiography) were 91%, 93%, 77%, and 98%. Two lesions were missed by MDCT, and 6 were overestimated to be in-stent restenosis. Although these data move us one step further in the assessment of stented segments, the stents in their study were relatively large (60% were  3.5 mm) and therefore more easily assessed, there was no patient with a "stent in stent" for previous restenosis, patients with renal failure (often with more calcified arteries) were necessarily excluded, and 12% of stents that were considered nonassessable and analyzed as restenosis in a secondary analysis would have to be taken into account in the real-world clinical setting. The binary restenosis rate of 19% in stented segments (majority were bare stents) would be lower with drug-eluting stents (DES), and the rather low 77% PPV for assessable segments was lower still for DES patients. On the other hand, the real clinical utility of MDCT may be the ability to rule out restenosis in the post-PCI patient; this certainly is feasible given the high NPV, which should be even higher in the presence of a lower rate of restenosis.
In a complementary paper, Meyer et al. (17) report the high accuracy of 64-slice MDCT for assessing coronary bypass grafts in an unselected symptomatic patient population. On a per-patient analysis in the 97% evaluable patients, MDCT diagnosed graft stenosis with high sensitivity (100%), specificity of 92%, PPV of 93%, and NPV of 100%, but including the nonevaluable patients for an intention-to-diagnose analysis, the resulting values were lower, and this would be the case in real-world patients. Good results were obtained for both arterial and venous grafts, albeit with lower sensitivity (93% vs. 99%) and lower PPV (86% vs. 96%) for arterial grafts, which are usually of smaller caliber. In 9 grafts, image quality was insufficient because of motion artifact (8 grafts) or numerous metallic clips (1 patient). What the investigators did not study, however, were the proximal and distal native segments, which may have clinical relevance as a cause of symptoms, especially in patients in whom bypass conduits are abnormal or occluded. Feasibility of assessment of the distal anastomosis has been variously reported for 74% (18) to 94% and 99% of grafts (15,19). Distal to the anastomosis, the coronary vessel may be relatively small and more difficult to assess. Feasibility of native vessel PCI after graft occlusion may depend on the distinction between high-grade and chronic total occlusion of the proximal vessel, a differentiation that may be difficult with MDCT.
What then is the current role of MDCT in the post-revascularization patient? Should every patient undergo MDCT angiography routinely after revascularization? Should this be repeated at regular intervals? Should we study only symptomatic patients and/or those with abnormal exercise or radionuclide imaging test results? Although only the last of these strategies seems to be appropriate at the present time, an increasing number of patients now undergo MDCT and the physician needs to integrate the findings into the overall clinical picture. When possible, MDCT findings should be compared with previous invasively obtained information. We have used MDCT in post-revascularization patients presenting to the emergency department, where MDCT-based patient triage allowed us to avoid hospital admission in a number of cases and to adjust clinical decision making regarding need for a repeat invasive strategy (20). In patients with an equivocal or nondiagnostic treadmill test result, MDCT allowed us to refine the selection of patients who require invasive angiography (21). Also, MDCT is useful in post-bypass patients scheduled for repeat invasive angiography, when prior information regarding graft patency or occlusion allows a shorter invasive procedure, particularly in patients with a complex surgical history. The MDCT images transmitted to the monitoring screens of the invasive laboratory already assist in interventional planning in a number of medical centers.
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Where Are We Heading?
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The MDCT technology is advancing rapidly, and dual-source (22) and other new technologies, such as 256-slice scanning (23), promise to simplify the test quite remarkably while improving diagnostic accuracy. Novel computer processing aims at automatic analysis of the coronary vasculature and coronary plaques. Other noninvasive modalities, such as magnetic resonance imaging (MRI), allow for high-quality images of cardiac anatomy and vascular plaque (24) and real-time MRI has been suggested as a guide for cardiac interventional procedures (25). The world of cardiac imaging is still evolving, but it is clear that the possibilities regarding diagnosis and management in the post-revascularization patient have improved considerably, and we are ready to integrate the new noninvasive imaging modalities into clinical practice.
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Footnotes
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* Editorials published in the Journal of the American College of Cardiology reflect the views of the authors and do not necessarily represent the views of JACC or the American College of Cardiology. 
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References
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1. Sones FMJ, Shirey EK. Cine coronary arteriography Mod Concepts Cardiovasc Dis 1962;31:735-738.[Medline]2. Nikolaou K, Flohr T, Knez A, et al. Advances in cardiac CT imaging: 64-slice scanner Int J Cardiovasc Imaging 2004;20:535-540.[CrossRef][Web of Science][Medline] 3. Achenbach S, Daniel WG. Computed tomography of the coronary arteries: more than meets the (angiographic) eye J Am Coll Cardiol 2005;46:155-157.[Free Full Text] 4. Raff GL, Gallagher MJ, O’Neill WW, Goldstein JA. Diagnostic accuracy of noninvasive coronary angiography using 64-slice spiral computed tomography J Am Coll Cardiol 2005;46:552-557.[Abstract/Free Full Text] 5. Mollet NR, Cademartiri F, van Mieghem CA, et al. High-resolution spiral computed tomography coronary angiography in patients referred for diagnostic conventional coronary angiography Circulation 2005;112:2318-2323. 6. Pugliese F, Mollet NR, Runza G, et al. Diagnostic accuracy of non-invasive 64-slice CT coronary angiography in patients with stable angina pectoris Eur Radiol 2006;16:575-582.[CrossRef][Web of Science][Medline] 7. Schuijf JD, Pundziute G, Jukema JW, et al. Diagnostic accuracy of 64-slice multislice computed tomography in the noninvasive evaluation of significant coronary artery disease Am J Cardiol 2006;98:145-148.[CrossRef][Web of Science][Medline] 8. Gertz SD, Cherukuri P, Bodmann BG, et al. Usefulness of multidetector computed tomography for noninvasive evaluation of coronary arteries in asymptomatic patients Am J Cardiol 2006;97:287-293.[CrossRef][Web of Science][Medline] 9. Ropers D, Rixe J, Anders K, et al. Usefulness of multidetector row spiral computed tomography with 64- x 0.6-mm collimation and 330-ms rotation for the noninvasive detection of significant coronary artery stenoses Am J Cardiol 2006;97:343-348.[CrossRef][Web of Science][Medline] 10. Muhlenbruch G, Seyfarth T, Soo CS, Pregalathan N, Mahnken AH. Diagnostic value of 64-slice multi-detector row cardiac CTA in symptomatic patients Eur Radiol 2006Sep 29;[E-pub ahead of print]. 11. Hoffmann U, Moselewski F, Nieman K, et al. Noninvasive assessment of plaque morphology and composition in culprit and stable lesions in acute coronary syndrome and stable lesions in stable angina by multidetector computed tomography J Am Coll Cardiol 2006;47:1655-1662.[Abstract/Free Full Text] 12. Pohle K, Achenbach S, Macneill B, et al. Characterization of non-calcified coronary atherosclerotic plaque by multi-detector row CT: comparison to IVUS Atherosclerosis 2007;190:174-180.[CrossRef][Web of Science][Medline] 13. Halon DA, Gaspar T, Peled N, et al. Assessment of luminal diameter of coronary stents using a novel 40 slice multidetector CT scanner Circulation 2004;110(Suppl):III563. 14. Gaspar T, Halon DA, Lewis BS, et al. Diagnosis of coronary in-stent restenosis with multi-detector row computed tomography J Am Coll Cardiol 2005;46:1573-1579.[Abstract/Free Full Text] 15. Pache G, Saueressig U, Frydrychowicz A, et al. Initial experience with 64-slice cardiac CT: non-invasive visualization of coronary artery bypass grafts Eur Heart J 2006;27:976-980.[Abstract/Free Full Text] 16. Ehara M, Kawai M, Surmely J-F, et al. Diagnostic accuracy of coronary in-stent restenosis using 64-slice computed tomography: comparison with invasive coronary angiography J Am Coll Cardiol 2007;49:951-959.[Abstract/Free Full Text] 17. Meyer TS, Martinoff S, Hadamitzky M, et al. Improved noninvasive assessment of coronary artery bypass grafts with 64-slice computed tomographic angiography in an unselected patient population J Am Coll Cardiol 2007;49:946-950.[Abstract/Free Full Text] 18. Schlosser T, Konorza T, Hunold P, Kuhl H, Schmermund A, Barkhausen J. Noninvasive visualization of coronary artery bypass grafts using 16-detector row computed tomography J Am Coll Cardiol 2004;44:1224-1229.[Abstract/Free Full Text] 19. Dewey M, Lembcke A, Enzweiler C, Hamm B, Rogalla P. Isotropic half-millimeter angiography of coronary artery bypass grafts with 16-slice computed tomography Ann Thorac Surg 2004;77:800-804.[Abstract/Free Full Text] 20. Rubinshtein R, Halon DA, Gaspar T, et al. 64 slice cardiac CT is a valuable new tool for triage and management of patients presenting to the emergency room with chest pain of uncertain etiology Circulation 2005;112(Suppl):II680. 21. Rubinshtein R, Halon DA, Gaspar T, et al. Usefulness of 64-slice multi detector computed tomography to improve diagnostic yield in patients with chest pain and negative or non-diagnostic exercise treadmill tests Am J Cardiol 2007In press. 22. Achenbach S, Ropers D, Kuettner A, et al. Contrast-enhanced coronary artery visualization by dual-source computed tomography—initial experience Eur J Radiol 2006;57:331-335.[CrossRef][Web of Science][Medline] 23. Funabashi N, Yoshida K, Tadokoro H, et al. Cardiovascular circulation and hepatic perfusion of pigs in 4-dimensional films evaluated by 256-slice cone-beam computed tomography Circ J 2005;69:585-589.[CrossRef][Web of Science][Medline] 24. Fuster V, Kim RJ. Frontiers in cardiovascular magnetic resonance Circulation 2005;112:135-144. 25. Lederman RJ. Cardiovascular interventional magnetic resonance imaging Circulation 2005;112:3009-3017.
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