There's a well-established medical technology that many physicians believe could help catch undiagnosed breast tumors in one-third to one-half of women -- yet it's not being used routinely. It's ultrasound imaging, a longtime fixture of obstetricians' offices. Some doctors use ultrasound along with traditional x-ray mammography in breast exams, but the majority have been waiting for clearer evidence of its benefits. And that's exactly what a key clinical trial now under way in the United States could provide.

At least half of women under 50 and about a third of older women have naturally dense breast tissue, making it harder to distinguish between healthy tissue and questionable masses in mammograms. Ultrasound can get around that problem because the different types of tissue reflect sound waves differently, says Wendie Berg, the leader of the trial and an independent breast-imaging consultant in Lutherville, MD. "Ultrasound is widely available and relatively inexpensive," she says. "It's reasonable to consider it for routine screening."