Making the Body Transparent

By Claudia Wallis

The mysteries of illness are revealed as never before

The throbbing of the brain to the beat of the heart, the coursing of blood through a maze of vessels, the dance of molecules in a working muscle, the stealthy growth of a tumor. For generations doctors have hunted for ways to see through skin and bone and into the whirring processes of life. The discovery of the X ray in 1895 by Wilhelm Roentgen opened the first window into the living body and inaugurated a new age in medicine. But anyone who has ever glanced at an X-ray film can perceive its Limitations. The picture gives little sense of depth, and while bones show up crisply enough, many of the softer tissues of the body are fuzzy shadows in shades of gray.

Ten years ago, doctors began to see more detail with a new kind of X-ray machine that uses a computer to construct clear, cross-sectional views of the body. The CAT scanner (for Computerized Axial Tomography) revolutionized radiology. But now that virtually every large hospital in the country has invested in one, at about a million dollars apiece, another revolution is under way: Nuclear Magnetic Resonance, or NMR. Currently being studied for approval by the Food and Drug Administration, the new technology is in experimental use at about half a dozen top U.S. medical centers as well as several overseas.

NMR exposes the internal landscape as never before. "Its development," says British Radiologist Brian Worthington of the University of Nottingham, "is as significant as the development of the X-ray machine one hundred years ago." Unlike CAT and other forms of X ray, NMR can "see" with clarity through the thickest of bones. Thus, without painful injections of contrast material, it can reveal damage from a stroke buried deep beneath the skull, find tiny spinal cord injuries, and make it possible to differentiate the gray and white matter of the brain. "For the soft tissue of the body," says Worthington, "NMR comes close to being the perfect imaging technique."

The revelations offered by NMR go beyond anatomical topography. Not only can doctors see internal organs, they can actually monitor certain processes occurring within them: blood moving through an artery, an arthritis-inflamed knee shrinking in response to steroid treatment, the reaction of a malignant tumor to therapy. "NMR opens up the whole wonderful world of in vivo chemistry," exclaims Neuroradiologist Sadek Hilal, who is testing the new technique at New York City's Presbyterian Hospital.

What makes NMR'S revelations even more remarkable is that they are produced without the ionizing radiation of X rays. In significant doses, X radiation can damage cells and may be a factor in causing cancer; it may be particularly dangerous to the rapidly dividing cells of children and pregnant women. NMR, by contrast, appears to be harmless. "We can look at the developing brain of an infant easily and safely," says Dr. Robert Steiner of London's Hammersmith Hospital.

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."

Even more dramatic applications may become available as NMR technology improves. Powerful new magnets, chilled with liquid helium to -270DEG C, not only enhance the images based on hydrogen nuclei, the most prevalent element in the body and the easiest to trace, but also make it possible to pick up nuclear magnetic signals from phosphorus, sodium, fluorine and certain carbon atoms. Doctors are especially excited about the prospect of working with phosphorus, since the energy for all of life's activities comes from chemical reactions involving this element. At the University of Pennsylvania, Dr. Britton Chance has been using phosphorus NMR to diagnose muscular disorders and to study the use of energy in working muscles. His cryogenic magnet is large enough to accommodate only a leg. But, he says, "we are on the verge of sticking the whole body into such magnets. Then we will be able to look at the heart or brain after stroke or injury, not only to see precisely where the damage has occurred but to assess the biochemical capability of the tissue to recover." Such information would greatly aid doctors in choosing a course of treatment.

Versatile though it is, "NMR is not going to replace everything," says Dr. Graeme Bydder of Hammersmith Hospital. "I believe it will have less importance in the abdomen and pelvis because existing techniques, including ultrasound, are very good." Nor is it as good as X ray in depicting fine detail of the bones. Whether the radiation-free technique can reliably detect breast cancer is not yet known, but results with current equipment have been disappointing.

There are also a few practical drawbacks to NMR. Its powerful magnetic field poses a potential hazard to patients with pacemakers and artificial joints and other implants containing metal. NMR costs about 50% more than a CAT: as high as $ 1.5 million for some of the simpler devices, and possibly double that for the strongest cryogenic models. Overhead costs are high too because of the need to house the machine in a huge, metal-free area that is sealed from such outside electromagnetic influences as FM and CB radio. The Cleveland Clinic plans to invest $3 million in a special NMR building.

Still, about 25 U.S. medical centers have NMR machines, on order and, according to General Electric, one of a dozen NMR manufacturers, there will be 150 in place by the end of 1984. Predicts Dr. Theodore Tristan, past president of the Radiological Society of North America: "We're going to see that every large hospital, as its CAT unit wears out, will want to replace it with an NMR system." The challenge then will be to learn how to exploit the tremendous potential of the new techniques. Admits Worthington: "We're just not clever enough yet to appreciate it all."

With reporting by Magda Krance, Mary Carpenter This file is automatically generated by a robot program, so viewer discretion is required.