The Future of Cardiac MRI

Abstract

Cardiac magnetic resonance imaging (MRI) is the newest noninvasive imaging technique to be used for the evaluation of patients with ischemic heart disease (1–3). MRI can be used to study myocardial viability, myocardial ischemia, cardiac function and metabolism, and coronary artery anatomy and flow (4). The recent scientific and clinical advances have been such that several small medical societies have started to focus almost exclusively on cardiovascular MRI (5). Each year the North American Society for Cardiac Imaging (www.nasci.org), the Society for Cardiovascular Magnetic Resonance (www.scmr.org), the Council on Cardiovascular Radiology of the American Heart Association and the International Society of Magnetic Resonance in Medicine organize multiple educational events to instruct imagers and practitioners (mostly radiologists and cardiologists) about the potential value of cardiac MRI for patients with ischemic heart disease. In 1999 the Committee for Cardiovascular Imaging, a joint effort of the American College of Radiology, the Radiological Society of North America, the American Roentgen Ray Society, and the American Board of Radiology, was created to address this renewed interest from the radiology community in cardiovascular imaging. One of the first actions of the committee was to create new courses on cardiovascular imaging which are being offered four times a year throughout the United States, with the first one held in June 23–25, 2000, in Chicago (www.acr.org). Recent dramatic improvements in the technology (i.e., newer and better cardiac MRI pulse sequences) and the efforts to teach the performance of coronary magnetic resonance angiography (MRA) to more end-users (radiologists and cardiologists) are both important. For a variety of reasons most practitioners and imagers are often reluctant to utilize cardiac MRI in the routine workup of patients with ischemic heart disease. In general, these physicians lack exposure to and training in cardiac MRI. Furthermore, these examinations are technically difficult and there is the need for cardiac gating which lengthens the duration of the MR study setup time. Large clinical studies which may prove the utility of MRI for ischemic heart disease are only now being performed or planned. But most important perhaps, as pointed out by Higgins (4), a key component of the MR evaluation of ischemic heart disease, namely coronary MRA, has not yet reached a sufficient level of technical maturity. Unfortunately, cardiac MRI technology is evolving so fast that most clinical trials cannot be completed before a technique becomes obsolete, thus creating the perception that the technology is not mature. Coronary MRA is one of the best examples of such recent technological evolutions in cardiac MRI. The early coronary MRA techniques appeared very promising (6), but because they acquired only one image per breathhold, were limited to 2-D acquisitions and required operator skills. These techniques never gained widespread use (7–9). Improved coronary MRA techniques employing navigator echoes, also referred to as “second-generation coronary MRA techniques,” followed, and allowed freebreathing and increased spatial resolution followed (10–13). Later, third-generation techniques allowed the acquisition of a 3-D volume within one breathhold (14). Hybrid techniques offer the greatest hope for fast and efficient coronary MRA with adequate spatial and temporal resolution (15–17). Although these newer coronary MRA techniques are nearly as easy to employ as a conventional computed tomography (CT) scanner, the average practitioner is not comfortable with this constant change and evolution in MR techniques. The use of cardiac MRI for the direct evaluation of myocardial viability and myocardial ischemia has seen a similar dramatic evolution. Cardiac MRI has become such a vast field that it is impossible to make general statements about its future, except to say that its importance will keep increasing. Cardiac anatomy, function and myocardial viability evaluation are all very important applications, and will one day be part of the “one-stop” noninvasive comprehensive cardiac MRI examination (2,18). In this chapter we will limit our comments about the future of cardiac MRI to those that relate to coronary vessels.