X-rays and magnetic resonance imaging are powerful tools in medicine, but neither tells doctors everything they want to know. To get a better picture of the structural effects and chemical details of various diseases, researchers are adapting a technology long used by satellites to study the ground below.

It's called "multispectral imaging," and it uses a camera and certain wavelengths of visible and infrared light to take pictures of moles and other surface structures. It can even photograph  internal structures like the brain, say, or a tumor, because some wavelengths can penetrate the body without harming it. By choosing wavelengths tuned to different constituents of biological tissues, such as water and fat, researchers can pick up otherwise invisible details, much as satellites can "see" the heat of a dense urban area using the right wavelengths of infrared light.

Engineers at several universities-many with funding from the National Institutes of Health-are working to develop these imaging tools for medical applications. Because they can operate in real time, multispectral imagers could, for example, help guide doctors during surgery. Alexander Gorbach, a research scientist at NIH's Clinical Center in Bethesda, MD, is building a system to help neurosurgeons distinguish between cancerous and normal tissue in a brain exposed for surgery-based on the fact that light bounces off the enlarged nuclei of cancer cells differently than it does off normal cells' nuclei. The imager could help brain surgeons know precisely where to cut.

The technology could also help doctors get medical data without putting patients under the knife. "That's one of the advantages, that you don't have to remove tissue to get information," says Michael Feld, director of MIT's Laser Biomedical Research Center. Feld is working on a system to determine the calcium content of plaques in arteries, which could tell heart specialists if they're likely to cause problems. Gathering such chemical clues is possible because each type of molecule reflects and absorbs light in a particular pattern.