Medicine: Making the Body Transparent

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In place of radiation, NMR uses magnetic forces, 3,000 to 25,000 times the strength of the earth's own field, to wrest information from the body's molecules. Physicists and chemists have appreciated this use of magnetism for more than three decades. In fact, American Physicists Felix Bloch and Edward Purcell won a 1952 Nobel Prize for showing how NMR techniques could be used to probe atomic nuclei.

The heart of the NMR device is a giant, doughnut-shaped magnet, large enough to enclose the patient's body, and strong enough to stop a watch within ten feet. A field that powerful has an equally dramatic effect on certain atoms in the body.

The nuclei of hydrogen, phosphorus and other elements with an odd number of protons or neutrons are themselves like tiny magnets; when placed within an NMR field, they line up like soldiers on command. To produce an image, the NMR machine emits a radio pulse that creates a second field at right angles to the first. The soldiers respond by doing a simultaneous quarter-turn toward the second power source. When the pulse is turned off, they flip back to the original position. This sequence produces a detectable electromagnetic signal. Each type of tissue in the body has a characteristic signal intensity and duration. Fed into a computer in the NMR system, the data create vivid, cross-sectional images of the body.

NMR is still in its infancy, but even the pictures available today can provide unprecedented insights. "In three out of 35 patients, NMR found brain tumors that CAT missed," says Thomas Brady, director of clinical NMR at Massachusetts General Hospital. "It has proved nearly 100% accurate in showing multiple-sclerosis lesions, while CAT has had a success rate that ranges from 5% to 35%."

At the Cleveland Clinic, Radiology Chief Edward Buonocore reports "superb" results with NMR imaging of the chest. Distinctions between lung tumors and normal tissue are clearer with the new technology, he says. "Any patient who has had his chest opened because a blood vessel was mistaken for a tumor would see the importance of this."

NMR pioneers also praise its power to depict blood and blood vessels. "It will provide the ability to see plaque buildup in arteries around the heart," predicts Thomas Budinger of the University of California at Berkeley. "Imagine studying coronary-artery disease throughout a person's lifetime without radiation and without injecting contrast material."