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Invited Commentary |
Department of Radiology, New York Methodist Hospital, Brooklyn, New York
There is an unnamed South American country where the tongue-in-cheek national motto is, "It is the country of the future and always will be." Clearly, there is an analogy between this aphorism and the future of cardiac MR imaging. Great strides in the development of appropriate software, cardiac and respiratory gating, high-speed gradients, and powerful magnets have resulted in the rapid image acquisition and seamless cine techniques necessary for high temporal resolution to image the beating heart. As a result of these advances, cardiac MR imaging should be competitive with other noninvasive techniques for evaluation of cardiac anatomy and function. Characterization of ventricular contraction abnormalities, determination of global and segmental ejection fraction, and grading of the severity of valvular stenosis and regurgitation can be performed. Filling defects within the cardiac chambers, such as thrombi or tumors, can be identified and characterized with high sensitivity. In addition, with the recent development of tagging techniques, detailed evaluation of cardiac motion can be achieved. Perhaps MR imaging has been most useful in the identification and postsurgical follow-up of congenital heart disease in both children and adults.
Despite these advantages, cardiac MR imaging is seldom ordered, with certain exceptions, and remains a distant third choice for noninvasive cardiac imaging after echocardiography and radionuclide imaging. In part, this lack of interest is due to important limitations of MR imaging in the evaluation of cardiovascular disease. The inability of MR imaging to demonstrate calcium and the challenge of complex cardiac motion limit the role of MR imaging for the detailed demonstration of coronary artery anatomy and disease. On the other hand, ultrafast CT and echocardiography, two competing modalities for diagnosis of heart disease, have similar disadvantages in the demonstration of distal coronary artery anatomy.
Other reasons for the slow development of cardiac MR imaging are many and include the control of the equipment by radiologists rather than the ordering cardiologists, the lack of professional manpower with expertise in cardiac imaging, the competition from neurologic and musculoskeletal studies for the limited amount of patient time available on MR imaging machines, the relative inability of the equipment to accept cardiac support equipment in the MR imaging suite, and a widespread lack of knowledge about what MR imaging can accomplish.
The preceding article by Dr Boxt goes a long way toward demystifying cardiac imaging. Dr Boxt has given us a primer for performing basic cardiac MR imaging. His goal is simple: to provide the reader with a step-by-step approach to produce a satisfactory MR imaging study. He certainly achieves this goal. He does not emphasize clinical scenarios in which MR imaging is clearly superior to other techniques for the diagnosis of cardiac disease, such as arrhythmogenic right ventricular dysplasia, which is best diagnosed with MR imaging and is not well diagnosed with other modalities. The problem of visualizing the coronary arteries needs to be addressed with careful efficacy studies to see whether any noninvasive procedure has the ability to satisfactorily demonstrate the coronary arteries when compared with angiography. The goal of the cardiac radiologist is to develop a "one-stop shopping" approach to cardiac MR imaging. To accomplish this goal, protocols need to be kept simple and the equipment should allow one to proceed through the computer menu quickly and without difficulty.
What are the advantages of MR imaging over its major competitors, CT (both ultrafast and conventional spiral) and, of course, echocardiography? MR imaging is readily available, although the appropriate cardiac imaging software is not, and as in echocardiography there is no ionizing radiation. Another major advantage of MR imaging over examination with ultrasound is the ability to visualize anatomic detail beyond the heart, including the great vessels, the lungs, and other supporting structures, and to image the right ventricle, which is difficult to evaluate with any modality but is best demonstrated with MR imaging.
The disadvantages of MR imaging include the inability to demonstrate calcium, and motion artifacts present more of a problem than in ultrafast CT or certainly echocardiography, a real-time technique that has no problem with motion. The future of MR imaging for the diagnosis of cardiovascular disease remains unclear, but contributions such as Dr Boxt's how-to manual will help bring this diagnostic option closer to the forefront of cardiac diagnosis.
Department of Radiology, Beth Israel Medical Center, New York, New York
I am grateful for this opportunity to respond to the kind comments of Dr Steiner. I do not wish to rebut his observations but rather would like to amplify several of his important points.
I agree with Dr Steiner that MR imaging has significant advantages for the evaluation of patients with congenital or acquired cardiovascular disease. I accepted the invitation to write the article because I think there is a great gap between the value of cardiac MR imaging and the ability of radiologists to perform it and interpret the results. I believe that the variance between claims of usefulness and the experience of many radiologists has discouraged the performance of cardiac MR imaging and impeded the growth of this important technology. This gap exists because of two very important reasons. First, the usefulness and value of cardiac MR imaging have been tremendously oversold. There is no question that the technique can provide images of exquisite contrast and spatial resolution and, when coupled with high temporal resolution acquisitions, can be used to visualize a host of congenital and acquired cardiovascular abnormalities. However, equation of great images obtained at a few large centers with mainstream clinical usefulness is hazardous. The ability to demonstrate wall motion abnormalities or defects in the interatrial septum, for example, does not make MR imaging the procedure of choice for demonstrating such abnormalities. The other issue concerning cardiac MR imaging is that examinations do take longer to perform, the images are subject to more artifacts, and the results may be difficult to interpret. In other words, the gap between expectations and reality is broad because expectations are inflated and the ability to produce meaningful data is limited. So long as radiologists have difficulty achieving the high-quality examinations they and referring physicians expect, they will shy away from performing them, which will impede their ability to improve and maintain examination quality.
My article is designed to close this gap by instructing radiologists who perform noncardiac MR imaging in the planning and performance of cardiac examinations. My hope is to identify, in a step-by-step manner, the issues involved in cardiac examination and describe a means of addressing and solving the problems inherent in such examinations. I hope to extrapolate from my experience; improved examination performance would breed improved confidence, and improved confidence would simultaneously deflate exaggerated expectations and expand the clinical usefulness of such examinations, thus encouraging requests for their performance.
I avoid discussing the relative merits of MR imaging versus other imaging modalities for the diagnosis of cardiovascular disease as well as the relative value of MR imaging itself for diagnosis of specific cardiovascular abnormalities. I do this partly because many such issues are controversial but mostly because the premise of the article is to provide a primer for MR imaging rather than an argument for its performance. The article is intended to provide the radiologist, when faced with a patient with cardiovascular disease, with a guide for help in the planning and performance of an examination and interpretation of the results to solve specific clinical problems. As Dr Steiner points out, the choice of examination technique is often out of the radiologist's hands. The value of this article should be to improve performance of cardiac MR imaging and interpretation of the results. Such improvement would encourage the integration of the radiologist into the process of examination choice. Blanket statements concerning the efficacy or value of MR imaging have raised expectations and limited growth in examination performance.
As my article conveys, I am a strong exponent of the more widespread performance of cardiac MR imaging. However, I believe that the basis for increased performance is better planning and performance of cardiac MR imaging rather than increased publicity for its performance. Cardiac MR imaging is no longer a technology looking for an application. The issue is not whether commercially available imagers can provide important diagnostic information. Older imagers have always been able to provide good images. Rather, the issue is how we can help radiologists improve the quality of their cardiac MR imaging examinations so that expectations are met. Whether MR imaging becomes the forefront of cardiac diagnosis depends on the skill and judgment of the radiologists who perform these examinations. In an era of increasing diagnostic choice and decreasing reimbursement, the future of cardiac MR imaging depends significantly on the ability of radiologists to acquire the skills to perform diagnostic studies and solve clinical problems and do so quickly and safely.
Related Article
RadioGraphics 1999 19: 1009-1025.
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