Coronary MR angiography.

Atherosclerosis, specifically coronary artery disease, is the most common cause of adult mortality in the Western Hemisphere. Cardiac imaging represents an enormous percentage of all diagnostic imaging procedures. In 1993, an estimated US $1.67 billion (or 32% of all costs for imaging) was spent in the United States by Medicare (Part B) for reimbursement of the 10 most common imaging procedures that are all primarily cardiovascular in nature. 84 Atherosclerosis remains an elusive, progressive, and devastating disease, despite the enormous investment of research dollars by government and industry. Invasive selective coronary angiography has long been and is still the gold standard for defining the site and severity of stenotic lesions in the coronary arteries. The functional significance of lesions can be determined with myocardial perfusion tests with and without stress using either nuclear cardiology, echocardiography, or most recently MR imaging. In the more recent literature, the importance of the mechanisms involved in plaque formation and rupture as well as thrombus formation has been emphasized. Plaque histology and plaque stability are and should be critical factors in predicting the importance of a small plaque or a coronary lesion for future events. Nevertheless, in the day-to-day practice of cardiology, the traditional criteria of lesion stenosis and physiologic significance of lesion severity (coronary flow reserve) are still routinely used. Thus, for the day-to-day clinical practice of cardiology, there remains the need to image the coronary vessel's lumen and to exclude the presence of significant coronary lesions. Today, conventional x-ray coronary angiography is used almost exclusively for the direct visualization of the coronary lumen. Intravascular ultrasound has recently provided an alternative but is still very invasive. 110 Noninvasive alternatives, such as echocardiography (for infants and some pediatric patients), electron-beam CT (EBCT) angiography, and MR angiography, are being evaluated. EBCT angiography offers a good solution, although it requires the use of x-ray radiation and the injection of a potentially harmful iodinated contrast agent. 2,3,4,21,107,141,153,154,157 Coronary MR angiography is less invasive; can be used in a wider patient population (e.g., those with renal failure); but is excluded in others (e.g., patients with pacemakers, and so forth). Efforts are being made to teach the performance of coronary MR angiography to the point where it can be used in many clinical settings with existing commercial MR scanners and pulse sequences. 36 The use of cardiac MR imaging in general has received a lot of attention recently and several medical societies (such as the North American Society for Cardiac Imaging and the Society for Cardiovascular Magnetic Resonance) and other groups now organize educational symposia to increase the numbers of users who can perform these studies. 142 Recent dramatic improvements in the technology (i.e., newer and better cardiac MR imaging pulse sequences) and this new trend to teach the performance of coronary MR angiography to more end-users (radiologists and cardiologists) are both important. This article reflects on these new trends in this subfield of cardiac MR imaging. The future role of coronary MR angiography was discussed 1 year ago in the American Journal of Roentgenology by Lee Rogers, Editor-in-Chief. 143 Dr. Rogers pointed out that coronary artery imaging is still difficult and technically demanding, but not impossible. Neither MR imaging nor EBCT have sufficiently solved their inherent problems to make noninvasive coronary artery imaging a clinical reality. But whenever a noninvasive procedure (even if not perfect) replaces an invasive one, the number of examinations has the potential of increasing dramatically. There is thus an enormous potential market for noninvasive coronary MR angiography. The manufacturers and users are extremely interested in this market. Potential turf battles between radiologists and cardiologists may erupt given the potential for new revenues. One should also not forget that in the work-up of patients with coronary artery disease the total atherosclerotic burden in the aorta, carotid, and femoral arteries is a good predictor of coronary artery disease. A good correlation has been shown between the severity of atherosclerotic disease in one arterial bed and involvement of the other vessels. 82 This also opens the potential for more involvement by imagers in noninvasive screening for ischemic heart disease beyond the already established involvement in coronary calcium screening. Measuring the intimal-medial wall thickness in the carotid arteries and the femoral arteries can be easily performed by most radiology practices using ultrasound and could also become an important parameter, besides the more traditional screening factors, for the early prediction of coronary artery disease. It is extremely important that we as radiologists keep ourselves well trained and informed of the latest advances in this subfield of cardiac MR imaging so that we can continue to participate in the performance of these cardiac MR imaging studies. But, in order to do this, we need to be knowledgeable about the coronary MR angiographic sequences available today on commercial MR imaging scanners. Radiologists need to be prepared to work with cardiologists on these new applications. In this article, we describe most of the coronary MR angiographic techniques that have been developed and tested in preclinical trials. We do, however, direct the radiologist who is not yet a specialist in cardiac MR imaging and coronary MR angiography to those MR imaging techniques that in our view seem most likely to provide good results in the hands of the majority of users.