doi: 10.1161/CIRCIMAGING.108.814574
Editorials |
Noninvasive Coronary Imaging
The Contest Between Magnetic Resonance and Computed Tomographic Coronary Angiography
From the Departments of Cardiology and Radiology, Erasmus Medical Center, Rotterdam, The Netherlands.
Correspondence to Pim J. de Feyter, MD, Departments of Cardiology and Radiology, Erasmus Medical Center, Room Hs 207, PO Box 2040, 3000 CA Rotterdam, The Netherlands. E-mail p.j.defeyter{at}erasmusmc.nl
Key Words: imaging • magnetic resonance imaging • tomography • noninvasive imaging
Noninvasive coronary imaging is often considered the Holy Grail among cardiologists and radiologists interested in the diagnosis and treatment of coronary atherosclerosis.1–3 That noninvasive coronary imaging would aid in establishing new prevention and treatment strategies in a wide range of clinical scenarios, ranging from early subclinical diagnosis of atherosclerosis in asymptomatic individuals to evaluation and monitoring of coronary stenoses in symptomatic patients with new onset of symptoms or with known coronary artery disease. Remarkable engineering accomplishments have made it possible to visualize the coronary arteries although they are small, tortuous, and do not run in a single plane. Cardiac and respiratory motion makes it difficult to "freeze" the heart to create a sharp coronary image. Two noninvasive diagnostic modalities have emerged, magnetic resonance coronary angiography (MR-CA) and computed tomographic coronary angiography (CT-CA), that allow visualization of the coronary arteries. Each technique has its own advantages and disadvantages (Table 1), and comparison of both contemporary techniques is the obvious way to establish which would be preferable in current clinical practice.
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Earlier studies compared 3-dimensional, navigator-gated, free-breathing MR-CA with CT-CA. In a small study of 27 patients, Gerber et al4 demonstrated that MR-CA had a higher diagnostic accuracy than 4-slice CT-CA in the evaluation of coronary stenoses, although both techniques had comparably high negative predictive values, which made them suitable to rule out significant coronary artery disease. In a follow-up study, the same group of investigators compared 3-dimensional, navigator-gated, free-breathing MR-CA with 16-slice CT-CA in 52 patients.5 Using visual assessment of coronary stenoses severity, they demonstrated that the diagnostic accuracy was similar for the 2 techniques. Using a similar study design in a larger cohort of 108 patients, however, Dewey et al6 demonstrated that 16-slice CT-CA compared favorably with MR-CA (Table 2).
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However, since the Dewey et al6 study, CT technology has further developed, and a 40/64-slice CT scanner was introduced for clinical use; therefore, it seemed timely to once again compare both techniques. In this issue of Circulation: Cardiovascular Imaging, Pouleur et al7 evaluated 77 consecutive symptomatic patients undergoing both free-breathing, whole-heart MR-CA imaging and 40/64-slice CT-CA imaging (Table 2). They demonstrated that the diagnostic performance of CT-CA was better than that of MR-CA because CT-CA was more robust and able to evaluate a higher number of coronary segments with a higher accuracy than was MR-CA. The authors of both studies, Dewey et al6 and Pouleur et al, 7 are to be commended for the high quality and integrity of analyses used in their respective studies. Earlier studies evaluating the diagnostic accuracy of either CT-CA or MR-CA have often excluded nonevaluable patients or nonevaluable coronary segments from the calculation of sensitivity and specificity of a noninvasive test compared with invasive CA. This approach results in reporting "unrealistic" high diagnostic accuracies. This is opposite to the studies by Dewey et al6 and Pouleur et al7, who both used an "intention-to-diagnose" analysis, which included evaluation of all patients and coronary segments; nonevaluable patients or coronary segments were not excluded but were graded as a positive CT outcome. This provides a reliable, clinically realistic outlook of the diagnostic performance of MR-CA and CT-CA.
The Pouleur et al7 study demonstrated that both techniques were reliable to rule out the presence of a significant coronary stenosis. Although not perfect, CT-CA performed better in the detection of coronary stenoses than did MR-CA. The diagnostic performances of MR-CA and 64-slice CT-CA were in line with the performances in other studies using contemporary MR-CA or 64-slice CT-CA techniques.8–11 The study by Pouleur et al7 also showed that neither technique is ready to fully replace conventional CA, a finding that is also in line with earlier studies.
In conclusion, both MR-CA and CT-CA are still imperfect. Initially, MR-CA was somewhat superior to CT-CA. But significant improvements in CT hardware and software, from a 4-slice to a 64-slice (or even higher) scanner, have been more rapid than improvements in MR techniques and, today, the contest regarding the diagnostic accuracy between the 2 noninvasive imaging modalities has been settled in favor of CT-CA. However, the fact that CT-CA is associated with inherent radiation exposure and contrast use, both of which may induce a small but nonnegligible risk of cancer mortality or renal insufficiency, will be a strong incentive to further develop MR-CA to the same (or even higher) level of diagnostic performance than CT-CA. This will then provide a true "harm-free" noninvasive coronary imaging modality that allows low-threshold repeat investigations to detect and monitor the often-unpredictable progression of coronary atherosclerosis. This may facilitate more effective intervention programs to reduce the occurrence of sudden death or nonfatal myocardial infarction, which now occurs as a first manifestation of coronary artery disease in 40% to 60% of otherwise "healthy" individuals. Let us hope that the contest between MR-CA and CT-CA continues and results in the rapid development of more robust and reliable CT or MR diagnostic modalities that allow more accurate detection and tissue characterization of the coronary plaques.
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Footnotes |
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The opinions expressed in this article are not necessarily those of the editors or of the American Heart Association.
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