macromolecules all provide possible ways that MRI can exploit variations in water in the body—even in very nearby and only slightly different tissue targets—to produce better pictures.

As Bradley described the intricacies of MRI, he clarified which particular tissues and conditions in the body yield the best MRI pictures. From a strictly clinical perspective, many tissues and processes are ideal candidates for MRI, though some are not. He and his colleagues touched on the reasons for some of these limitations but also suggested how the expanding horizons of MRI research are encompassing more and more clinical diagnostic situations. As more sophisticated methods of scanning, more discerning contrast agents, and altogether new techniques are refined, the potential clinical scope of MRI will expand.

In the world of modern clinical medicine, however, practitioners face a number of practical considerations. The machinery and staff for a comprehensive MRI center cost millions of dollars a year and patently must be supported by larger institutions or hospitals, many of which have not installed MRI centers. Clinical and cost considerations aside, some patients are not suitable candidates for MRI because they cannot tolerate the conditions of the procedure, physically or psychologically. Usually the patient must climb into a large tunnel, hold still for 10 or 15 minutes, and perhaps remain for two or three times that long for several series of images. The noise and isolation of the machines have also presented problems for patients. Thus MRI is but one of a number of approaches to imaging the body. X-ray procedures continue to be refined, sonogram imaging has many applications, angiography and arthrography give doctors a direct approach to the problem area, and there may always be certain situations where the MRI procedure is categorically impossible. And yet, if cost and other practical impediments can be overcome, the future value of MRI to diagnosis is almost without limit. As Bradley described it, MRI "really has become the most powerful diagnostic tool in clinical medicine since the discovery of the x ray."

Powerful, and also sophisticated. The science of radiology, following the discovery by Roentgen in 1895 of x rays, created a formal branch of medicine devoted exclusively to diagnosis. Medicine, of course, has for millennia involved its practitioners in the process of ascertaining what it was they were undertaking to treat. Said Hippocrates: "The capacity to diagnose is the most important part of the medical art." But not until the 20th century did that part become so distinct as to involve separate, specialized doctors and technicians whose relationship with the patient was conducted primarily through the imaging machinery. This development has continued as other

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