What Digital Can Do

When you finally get your mammogram, chances are, you won't be paying too much attention to the equipment. But there's a quiet revolution going on in the technology of mammography, as analog systems make way for various digital techniques. The promise of digital mammography is that it will give doctors a more detailed picture of breast tissue--and thus improve on their ability to pick out tiny abnormalities. Physicians are beginning to appreciate the added control the technology offers but agree that the procedure is not quite ready to replace film mammography--the gold standard. This view is likely to guide the Institute of Medicine's recommendations on the value of digital mammography and 17 other screening methods, expected to be released this week.

Screening for breast tumors is a bit like searching for a penny in a sandstorm. Radiologists look for specks of calcium no bigger than a grain of sand; in a certain pattern, the specks could indicate a tumor. The dense tissue of the breast, particularly in younger women, makes it difficult to isolate these spots on fixed X-ray film, so it's not surprising that doctors reading mammograms pick up only about 85% of the tumors that are there.

Digital mammography improves these odds by giving radiologists electronic eyes. The picture is taken the same way--by sending X rays through breast tissue compressed between two small plastic plates. But instead of transferring the X-ray image to film, digital mammograms translate the picture into bits of information that are stored on a computer. The radiologist can then manipulate the image by zooming in on problem areas or adjusting the contrast in bleak, featureless regions to single out suspicious growths.

At least that's the promise. It's still too early to tell whether digital mammograms are better at actually detecting tumors. So far, only one type of machine has been approved by the Food and Drug Administration, and only one study, published this month, has compared the two techniques head to head. The study, which compared the mammograms of 7,000 women screened using both technologies, showed no difference in the ability of digital and film images to pick up cancerous growths.

There are other benefits to going digital, however. The same study showed that because radiologists could adjust the images, they needed fewer retakes, sparing women the discomfort (and extra radiation) of a repeat mammogram. Also, digital systems upgrade more easily to accommodate future innovations, such as software filters that will allow doctors to "subtract" out healthy tissue and show only tiny tumors. "There are a lot of exciting possibilities down the road," says Dr. Etta Pisano of the University of North Carolina at Chapel Hill, who will be heading up a large study comparing analog and digital mammography later this year. "The technology is still in its infancy."