WASHINGTON - (AP) Remember peeking through a View-Master? Scientists are using the same concept behind the classic kids' toy to try to see mammograms in 3-D.

The goal: A better way to check for breast cancer in women with breasts too dense for today's mammograms to give a clear picture.

Radiologists donning 3-D glasses isn't the only potential aid. The Mayo Clinic in Rochester, Minn., is testing a new kind of breast camera that might challenge the images of those far pricer MRI exams now reserved for the most high-risk women, but at a fraction of the price.

Both technologies still are experimental. But the research is being watched closely because the need is so great: Half of women younger than 50 and a third of women over 50 are estimated to have dense breasts.

In addition to a harder time viewing any brewing tumors, women with dense breasts have a higher risk of getting breast cancer, too.

Only a mammogram can tell if your breasts are made up more of dense or easier-to-examine fatty tissue. But if a doctor warns that you have dense breasts, there's little good advice on how to get a better cancer check today.

"It's a major issue in the field now, more and more, how to address the imaging needs of women with significant breast density," says American Cancer Society screening specialist Robert Smith. "We and women and everyone else is kind of left wondering what would be best under what circumstances."

But, "we can do better than we're doing," predicts Dr. Mary S. Newell, assistant breast-imaging chief at Emory University in Atlanta, who is testing the 3-D approach.

Mammograms are X-ray exams that hunt denser spots in normal breast tissue, shadows that might signal a tumor. Regular mammograms starting at age 40 help reduce deaths from breast cancer by finding tumors when they're smaller and more treatable.

They're far from perfect, however, and dense breasts may be the X-rays' biggest hurdle.

Some doctors already give women with dense breasts an ultrasound exam -- the same sound-wave test used to view a developing fetus -- in addition to a mammogram. A handful of studies conclude ultrasound improves cancer detection but it remains controversial. Other women seek MRIs, which detect blood-flow changes that could signal cancer. But they're not recommended solely for dense breasts, partly because of their $1,000-plus price. Both options trigger a lot of false alarms by spotting suspicious areas that turn out to be fine.

Enter the new technologies:

• Mammograms are two-dimensional, flat pictures of a surface that's simply not flat. When technicians literally smush women's breasts into the mammography unit, they're trying to spread the tissue out so less is hidden from the X-ray. "Stereo mammograms" allow radiologists to see those X-ray images in 3-D, so that a small spot on the bottom might not be hidden by normal tissue laying over it.

We have depth perception because each eye gets a slightly different view, allowing your brain to construct a 3-D view when it overlays the two, explains Dr. Newell at Emory. That's the concept behind stereoscopes, gadgets that help people see pictures in 3-D like the old cartoons of a View-Master.

Stereo mammograms, being developed by Cambridge, Mass.-based BBN Technologies, work essentially the same way. Separate X-rays are taken at slightly different angles. Then radiologists wear glasses that make each eye see a separate image on special monitors. The brain "reads" that as a single, 3-D view.

In a soon-to-be-published study, Emory radiologists gave nearly 1,500 women at increased risk of breast cancer both a mammogram and a stereo mammogram. Different radiologists analyzed each test. When researchers put together the results, the stereo mammograms increased detection of cancer by 23 percent, Newell says. Another plus, it decreased false-alarms by 46 percent.

• The Mayo Clinic's so-called molecular breast imaging, or MBI, takes a different approach -- detecting how tumorous tissue acts instead of how it looks.

Doctors inject women with a drug known as a radioactive tracer, one cardiologists have used in heart stress tests for years. It tends to briefly collect in breast tumors, lighting up for viewing when Mayo switches on a small gamma camera.

The exam can be done in the same visit, even the same room, as a mammogram, while MRIs require injecting a different drug and spending an hour inside a doughnut-shaped magnetized machine, notes Mayo radiology fellow Carrie Beth Hruska.

Mayo researchers compared the records of 48 high-risk women who got both an experimental MBI and, within a month, a regular MRI. The faster MBI detected almost as many cancers -- 51 tumors in 30 patients -- as did the proven MRIs, which found 53 cancers in 31 patients, Hruska told a Defense Department breast cancer conference last week.

Stay tuned: Mayo just finished a study of 2,000 women comparing the gamma-camera technique to standard mammograms, and Hruska says additional government-funded studies at other hospitals will begin later this year.