SAN FRANCISCO — "You'd better remove your watch," says Dr. Michael C. Weiner cheerfully as a visitor enters his laboratory in the basement of the Veterans Administration Medical Center here. "And leave behind your credit cards. The magnetic field can ruin them, too."
Under its protective canopy, the source of this potential mischief dominates the lab. With its tunnel-like openings at each end, the large pickup-truck-size contraption vaguely resembles a CT (computed tomography) scanner. And like such high-tech X-ray machines, Weiner's monster almost swallows up the patient during an examination.
Both are diagnostic devices, capable of revealing many of the body's secrets. But there's an important difference. Once the patient--or at least the bulk of him or her--is slid into Weiner's machine, he's exposed not to X-rays but to a powerful magnetic field many thousands of times stronger than the Earth's.
While such a strong dose of magnetism may be hard on non-quartz watches or credit cards (to say nothing of pacemakers and other electro-mechanical devices), it ordinarily poses no threat whatsoever to people, Weiner says. Indeed, it may do them a lot of good.
Without biopsies or other intrusive procedures, the technique lets doctors tell how the patient's body is working down to the level of the chemistry of the cells. For the first time, metabolic processes can be studied non-invasively almost as they occur. "You don't have to resort to a scalpel, needle or radiation," Weiner says.
This medical marvel goes by the name of magnetic resonance spectroscopy (MRS). Although not generally available yet, it is being actively explored for clinical use by half a dozen medical research teams across the United States, including Weiner's unit, which is also affiliated with the nearby UC San Francisco. "The goal," he says, "is to develop MRS as a major new tool in the diagnosis and treatment of disease."
Dr. William Bradley, head of the magnetic resonance program lab at the Huntington Medical Research Institutes in Pasadena, adds, "There's at least a 50-50 chance we'll be doing clinically useful things with MRS within three years."
While MRS provides data readings of the chemistry of small, specific areas of the body, its close kin, magnetic resonance imaging (MRI), produces actual detailed images of the interior of the body. Both techniques operate through a novel use of magnetic fields and radio waves that in effect turn the body's atoms into little radio transmitters that broadcast clues to its inner workings.
Since its introduction less than a decade ago, MRI has grown dramatically. About 1,200 magnetic resonance scanners, each costing $1 million or more, are in use in the United States, about a quarter of them in California. Bradley's team leads the state, having done about 15,000 scans in the past five years.
Nowhere was the field's growth more evident than at the recent annual meeting here of the Society of Magnetic Resonance in Medicine. Only 8 years old, the Berkeley-based society attracted more than 2,500 physicians and scientists from a score of countries. They heard more than 1,200 scientific papers and saw manufacturers such as General Electric, Siemans, Philips and Diasonics display a dazzling array of new equipment as they compete for the $1-billion-a-year scanner market.
Both imaging and spectroscopy depend on a physical phenomenon called nuclear magnetic resonance (NMR) discovered in the 1930s. Physicists found that atomic nuclei--the centers of atoms--absorbed or emitted tiny amounts of energy if they were excited by rapidly changing magnetic fields.
In the 1940s, physicists Felix Bloch at Stanford and Edward Purcell at Harvard showed independently that these telltale signals, called spectra, could be used like fingerprints to identify atoms or molecules. In 1952, the two researchers shared the Nobel Prize in physics for their pioneering work.
NMR spectroscopy soon found a home in chemistry where it was put to work identifying and analyzing a wide variety of materials. It was also of interest to medical researchers because the magnetic fields could be used to study living tissue without destroying it.
But the next big step was not possible until two developments took place. Scientists could not create images without high-speed computers, capable of processing and assembling the flood of signals from a subject. They also needed powerful magnets to produce strong, sustained magnetic fields.
By 1974 scientists at the University of Aberdeen in Scotland displayed the first magnetic resonance image of a living creature, a cross-section view of a mouse. They used emissions from the nuclei of hydrogen atoms, the simplest element, consisting of single protons.
