The noble gas xenon, polarized by a laser and then inhaled by a rat, lights up the lungs and heart as seen in front (first row) and top views. Differences in the concentrations of xenon in blood (A and D), tissue (B and E), and gas (C and F) offer

Head Full of Xenon?

ATLANTA--Known to comic book aficionados as a potent superhero, xenon--in real life, a mild-mannered noble gas--may soon turn its super powers to medicine. Physicists have used xenon to generate images of blood flow through heart, lung, and brain tissue in rats. The research, presented here yesterday at a meeting of the American Physical Society, could be a promising alternative way to diagnose human disease via high-resolution magnetic resonance imaging (MRI).

Xenon, an inert gas, is valued by doctors for its anesthetic properties. In 1994, a team led by chemist Mitch Albert of the State University of New York, Stony Brook, showed that xenon can also light up air flow in the lungs, which eludes standard MRI techniques. The team "hyperpolarized" xenon atoms with a laser beam, aligning their spins to enhance their responses to a magnetic probe. In this way, inhaled xenon allows MRI to scan air-filled cavities. Another group found last year that xenon and the noble gas helium can produce clear signals in magnetic fields far weaker than those used in today's bulky MRI machines (ScienceNOW, 22 October 1998).

Now, researchers have found that xenon can trace how gases traverse the barriers between blood and tissue and between tissue and air. Biophysical chemist Scott Swanson of the University of Michigan, Ann Arbor, and his colleagues injected tiny doses of hyperpolarized xenon into the lungs of a rat immobilized in an MRI probe. Xenon atoms stay polarized in the body for up to 30 seconds, long enough for the gas to be absorbed into the bloodstream and circulate into the tissues of blood-rich organs. Subtle differences in the shapes of the polarized atoms within each medium--air, blood, and tissue--let the team image the patterns of blood coursing through the rat's hearts, lungs, and brains. "This could be very useful to pinpoint blockages in normal blood and air flow," such as in emphysema and fibrosis, Swanson says. Those features appear hazy using current technologies.

Probing the workings of the brain and other organs with xenon has "tremendous potential," says atomic physicist Gordon Cates of Princeton University in New Jersey. "Noble gases can give us much greater resolution than the functional MRI methods used today," he says. The U.S. Food and Drug Administration still must approve xenon for use in clinical MRI trials, Cates notes. He thinks that won't pose a problem, because patients already inhale xenon to enhance brain scans using tomography, another imaging technique.