New digital mammograms more accurately detect breast cancer than a standard mammogram for a significant group of women. That's the conclusion of a large government study that appears today in the online edition of the New England Journal of Medicine.

Digital mammograms capture images on a computer instead of the film used in traditional mammograms. The digital exam, albeit more expensive, can pick up more shades of contrast than film does. But until now, studies have shown that digital mammograms aren't more effective than the older form.

The four-year study monitored nearly 43,000 women with no signs of breast cancer. They had both traditional and digital mammograms and were tracked to see if they later got breast cancer. Then researchers looked back at the two types of mammograms to gauge their accuracy. The study found that overall, digital and traditional mammograms were similarly accurate in diagnosing cancer. Yet for certain groups of women—those younger than 50, women with dense breasts, and women who still get menstrual periods or are on the verge of menopause (those who have had a period within a year of the exam)—the digital mammograms are between 14 and 27 percent more accurate. The rates of false positive results were similar between the two tests.

About 65 percent of women in the study fit into one of those categories, though that proportion may vary in the general population. (Ask your doctor if your previous mammogram determined that you have dense breasts.) For these women, digital mammograms may be worth seeking out, though currently only 8 percent of mammography units have digital systems. Ask your doctor if one is available in your community. Even if you are in one of the affected groups, it's much more important to go ahead with a scheduled mammogram than to hold off until you can find a digital one, says the National Cancer Institute, which sponsored the trial. And if you've had a mammogram in the past year, there's no need to schedule an additional, digital mammogram before your next regularly scheduled test.

The study wasn't designed to see if digital mammography would actually save women's lives. But the NCI says that regular mammography has been shown to reduce the risk of death from breast cancer by 18 to 30 percent, so there is reason to believe that for the women helped by digital mammography, the benefit will be at least as good and possibly better. In addition, notes Emily Conant, chief of breast imaging at the University of Pennsylvania Medical Center and an author of the study, the kinds of tumors found by digital mammography and missed by film were the more serious, invasive type.

It's important to note, she adds, that some cancers were missed by both kinds of mammography. "It tells us yet again that mammography is not perfect," she says. "We are taking an established technique...and making it better." In the future, she says, women's screening recommendations will most likely be customized by age, breast density, genetic risk, and other factors.

The digital tests, while more expensive for healthcare providers, have additional benefits: They make it easier to store, share, and transmit mammography records.

Find out more: Go to the U.S. News guide on breast cancer to get in-depth information about symptoms, tests, treatment, and prevention.