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Technique zaps and maps lungs, heart.

No two parts of the body conduct electricity in exactly the same way. Researchers have now taken advantage of those differences to create an inexpensive imaging technique called adaptive current tomography (ACT). In ACT, the image's color or contrast varies with the tissue's resistance to electrical current.

Developed by mathematicians, engineers and biologists at Rensselaer Polytechnic Institute in Troy, N.Y., this technology relies on mathematical magic. A complex algorithm derives each image from data gathered by 32 electrodes placed in a circle around a patient's chest, says biomedical engineer Jonathan C. Newell, who coordinates the project.

Each electrode sends and receives tiny currents to and from all the other electrodes. Rather than travel straight across the body to opposite electrodes, says Newell, a current will follow the path of least resistance -- snaking around bone, for instance. All these currents emitted from the electrodes create a complex array of data, he says.

For imaging, the computer program first uses the voltages picked up by each electrode to calculate the resistance of the adjoining tissue, Newell explains. It then skips over the outermost layer of tissue and reconstructs the resistance of the next layer, repeating the procedure until it has mapped the whole cross section.

Though lacking fine resolution, the blurry images may still prove useful. "We expect [ACT] can be used for monitoring for water in the lungs," says Newell. This potentially dangerous buildup, called pulmonary edema, often escapes early detection. However, even a little water will alter the resistance of the lungs enough for ACT to sense a problem, says Newell. This fall, he plans to have physicians evaluate this potential application in people who have undergone surgery.

A tissue's resistance decreases 2 percent for every Celsius degree of increase in its temperature, so the new technique may be useful as a remote thermometer in certain cancer treatments, Newell adds.
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Title Annotation:adaptive current tomography
Publication:Science News
Article Type:Brief Article
Date:Jul 11, 1992
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