Changing the Image; April 1995; Scientific American Magazine; by Schneider; 1 Page(s)

Few would quibble with the value of screening for breast cancer, but even at its current level of maturity and appreciation, the art of x-ray mammography still shows a glaring flaw. It often fails to detect malignancies. In women younger than 50 years, for example, it misses existing cancers nearly half the time. So some medical researchers are cautiously contemplating screening for breast tumors with magnetic resonance imaging (MRI), a technique that probes the human body with a combination of magnetic fields and radio waves.

Certain women stand to benefit most from MRI: their breasts contain more fibrous or glandular material and less fat than is typical, and this constitution makes their breast tissues prone to scatter or severely attenuate x-rays. For these women (perhaps 40 percent of the female population), mammography renders images that are little more than a cloudy blur that prevents physicians from readily seeing the subtle architectural distortions indicative of cancer. Although some breast cancers signal their presence through the fog by creating microcalcifications that, like bone, leave bright spots on x-ray negatives, many malignancies do not contain these tiny radiographic beacons. Hence, for a woman with "dense" breasts, a doctor's normally assuring statement that no evidence of cancer appears on her mammogram has little weight.