There's also concern by researchers that the combo technology exposes women to more radiation than from 2-D alone. Currently, women can get a 3-D mammogram only in combination with the standard 2-D kind until there's more evidence that 3-D is as effective as traditional mammograms for detecting cancer.

Monsees believes the technology could eventually reduce the number of "false positives"— women who get called back for more screening because of questionable results with their standard mammogram — but it's too early to tell yet. Currently, about 10 percent of the 40 million women getting screening mammograms annually get a callback.

Diagnostic radiologist Carol Lee, M.D., of Memorial Sloan-Kettering Cancer Center in New York, agrees that 3-D mammography could reduce the number of callbacks, but "in effect you're doing two studies on every woman" and all of them are getting at least double the dose of radiation "in an effort to benefit a small number of women," she says. A new method that could combine the technologies but reduce radiation exposure by half is under development.

There's also the matter of cost. Those 3-D images — which can range from no extra charge at some facilities to more than $100 at others — are generally not covered by Medicare or private insurance. Aetna, for example, considers 3-D mammograms "experimental and investigational because of insufficient evidence of its effectiveness." And United HealthCare says that they are "unproven for the screening and diagnosis of breast cancer."

Yet many radiology centers promote the 3-D mammogram in gee-whiz terms, declaring it "a state-of-the-art technology," "a tremendous advance in our ability to detect breast cancer on mammography," "the latest breakthrough in mammography" or a "revolutionary screening tool."

That sort of aggressive promotion may be necessary because the machine costs around $700,000 plus annual service fees. The extra amount patients pay help doctors recoup that expense.

There's also the question of whether the new technology is more beneficial to younger women with dense breast tissue, where tumors may be harder to spot, than to older women. Generally after menopause a woman's breast tissue becomes less dense.

Radiologists can determine breast density when they examine a mammogram. "Women with dense breast tissue have a slightly but not dramatically increased risk of breast cancer," says diagnostic radiologist Constance Lehman, M.D., professor of radiology at the University of Washington in Seattle, who will be involved in a clinical trial of 3-D mammograms starting this year.

"If I were asked if I wanted 3-D, my first question would be, 'What's my breast density?' " she says. Your doctor or radiologist will be able to tell you if you have dense breast tissue.

You may want to ante up the extra money if you have dense breasts, a family history of breast cancer, or a gene mutation that ups your risk of developing breast cancer. But don't be hard on yourself if you choose to pass up 3-D. Until we know if 3-D mammography lives up to expectations, the most important thing is to stay on schedule with the trusty 2-D kind, still the gold standard for spotting breast cancer.

Nissa Simon frequently writes about health and science.

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