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Dr. Sharp replies To the Editor: Beattie and colleagues have described their experience with a 1.0 Tesla (T) extremity magnetic resonance imaging (MRI) machine and quote articles by others. In my editorial I purposely did not review the experience with the 1.0 T machine. Experience with this machine is extremely limited and the issues of tradeoff with the more expensive, standard 1.5 T, or even more powerful equipment, are not yet well defined. Those with experience with the 1.0 T machine report that the image quality approaches that of a 1.5 T device. Further, as Beattie, et al note, short-tau inversion recovery (STIR) images can be obtained with the lower field equipment. This early experience is encouraging and may mean that sufficient quality of the images produced will make it possible for rheumatologists and orthopedists to take advantage of the greater comfort and convenience of an "office" MRI. However, the cost advantage when comparing 0.2 T versus 1.5 T to 1.0 T versus 1.5 T is greatly decreased, although not completely abolished. It should be noted that 1.0 T is said to be the highest power that can be used in a configuration that will accommodate inserting a single extremity. Because the 1.0 T equipment has been marketed only recently, it is not clear that the ultimate cost of the machine can be predicted or, for that matter, whether there will be sufficient demand to sustain a market for this product. However, the current price is not attractive for the solo practitioner or small groups. It seems likely that only institutions that can use the 1.0 T machine as supplementary equipment to accommodate patients who have difficulty when imaged in the standard MRI machine, because of active arthritis, physical deformity, or claustrophobia, will find it attractive in the early stages of its availability. Only time will tell whether it will take 5, 10, or 20 or more physicians in a single group who have large numbers of patients who would benefit from the advantages of an extremity machine to make the instrument economically attractive. Beattie and colleagues are to be commended for pioneering this effort, but it will take many more studies comparing the 1.0 T to the 1.5 T equipment to be able to accurately evaluate the difference in quality of image and whether image quality difference ever compromises information needed for decision-making and if so, how often. Even with the higher powered magnet in the new equipment the question is still, what are the tradeoffs and do any of them compromise patient care? JOHN T. SHARP, MD, Affiliate Professor of Medicine (Rheumatology), University of Washington, Seattle, Washington 98110, USA. Address reprint requests to Dr. Sharp. E-mail: johntsharp@comcast.net
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