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Over the past decade, cardiovascular magnetic resonance imaging (MRI) has emerged as the gold standard for the evaluation of ventricular systolic function, as well as for evaluation and tissue characterization in ischemic and nonischemic cardiomyopathy.1 Cardiovascular MRI is reproducible, having a high spatial resolution, a relatively high temporal resolution, and no geometric assumption. Consequential to advances in both hardware and software, the imaging time is now considerably shorter than ever before.
Recently, the introduction of delayed-enhancement (DE) MRI provided physicians with a simple technique for visualizing myocardial scarring and fibrosis with an accuracy and resolution unmatched by other current noninvasive imaging techniques (Fig. 1). Furthermore, DE-MRI does not necessitate the use of pharmacologic stress or ionizing radiation. Various researchers have demonstrated that the extent of DE predicts myocardial functional recovery after revascularization, thereby providing cardiologists and cardiovascular surgeons with a valuable tool in selecting appropriate patients for revascularization. Our group recently demonstrated that after adjustment for important traditional prognosticators, such as ejection fraction and age, the presence and the degree of DE (the higher the degree, the worse) is an independent predictor of all-cause death in patients with and without coronary artery disease.2 Future prospective studies will be required to determine whether DE-MRI can be used as a novel risk-stratification tool for patients with either ischemic or nonischemic cardiomyopathy.
Single-photon-emission computed tomography (SPECT) and positron-emission tomography (PET) are widely used in the clinical assessment of myocardial perfusion and ischemia. In evaluating myocardial perfusion, cardiovascular MRI has the advantage of offering a relatively high in-plane spatial resolution (2–3 × 2–3 mm) that allows physicians to distinguish between subendocardial and transmural perfusion defects (Fig. 2). The recently reported multicenter, multivendor MR-IMPACT trial (Magnetic Resonance Imaging for Myocardial Perfusion Assessment in Coronary Artery Disease) showed that at experienced centers (using a gadolinium dose of 0.1 mmol/kg), cardiovascular MRI performs favorably in comparison with SPECT.3 Because cardiovascular MRI can provide additional ventricular functional and myocardial viability information in the same session, this approach is an attractive “one-stop–service” technique in the evaluation of coronary artery disease.
The past decade has seen a remarkable advance in multislice computed tomography (MSCT), which has evolved from a single-source to a dual-source technique. With the latest 320-slice MSCT, physicians can scan the entire heart in a single heartbeat. Coronary artery calcification (CAC) can be quantified by MSCT. Because CAC indicates the presence of atherosclerosis, even in asymptomatic patients, and predicts future cardiovascular events,4 the evaluation of CAC can identify patients who are at increased risk and can provide further risk stratification (in addition to the Framingham risk score). Multiple studies have consistently shown that MSCT has a high specificity and negative predictive value in the evaluation of coronary artery stenosis, thereby providing an important tool for ruling out obstructive coronary artery disease. However, the presence of anatomic stenosis does not necessarily imply significant functional stenosis. This fact was well illustrated by Meijboom and coworkers5 in a study that compared MSCT with intracoronary fractional-flow-reserve (FFR) analysis. Using an FFR of <0.75 to define a significant stenosis, the researchers found that the sensitivity, specificity, and diagnostic accuracy of quantitative MSCT were 50%, 75%, and 71%, respectively. The presence of intermediate lesions on MSCT frequently necessitates further functional testing. Nevertheless, multiple studies have shown that appropriately selected patients—those who presented at the emergency department and underwent MSCT that showed no obstructive disease—could safely be discharged, which reduced hospital length of stay and costs.
Recent studies have shown that prognostic information can also be obtained from MSCT. Like invasive angiography, MSCT can indicate the extent of underlying arterial stenosis, as well as the number of vessels involved.6 These data are predictive of all-cause death, in addition to cumulative cardiac events. Using state-of-the-art scanners, investigators have also begun to explore, with encouraging results, the role of MSCT in the assessment of myocardial perfusion and myocardial viability.
Address for reprints: Benjamin Y.C. Cheong, MD, Advanced Cardiovascular Imaging, Department of Radiology, MC 2–270, Texas Heart Institute at St. Luke's Episcopal Hospital, 6720 Bertner Ave., Houston, TX 77030
Presented at the 9th Texas Update in Cardiovascular Advancements; Houston, Texas; 4–5 December 2009
Program Director: James T. Willerson, MD