But the potential benefits of the new technology remain up for debate, since it arrives as the value of mammography screening is being questioned. Critics say it prevents only a small number of breast cancer deaths but increases the number of women treated for early non-aggressive cancers that might otherwise have gone undetected and never would have spread. Some cancer specialists, though, have passionately argued against deterring women from breast cancer screening since science can’t determine which cancers might become deadly.

Adding breast tomosynthesis to standard mammography improves the accuracy of a radiologist’s diagnosis by about 7 percent with fewer false positive findings, according to a new study conducted by Massachusetts General Hospital researchers and others that was published last month in the journal Radiology. “It’s becoming clearer that this is the future,” said study leader Dr. Elizabeth Rafferty, head of breast imaging at Mass. General. “It’s a rare test that allows you to increase true positives and decrease false positives.”

For the past eight years, Rafferty has been testing the effectiveness of 3-D mammograms — with funding from Bedford-based Hologic — helping the company gain approval from the US Food and Drug Administration in February 2011 for the first and only breast tomosynthesis device on the market. Mass. General now offers the screening to two-thirds of women who come in for their annual mammograms.

Breast tomosynthesis is performed just like a mammogram — with the breast flattened between two plates like a pancake — except the X-ray camera rotates to snap 15 images from all angles. Software designed for the machine synthesizes the images to create a 3-D rendering of the breast that radiologists can examine layer by layer, instead of examining the bird’s eye view from the traditional 2-D X-ray.

About 30 percent fewer women are called back for a repeat imaging test, resulting from a vague or suspicious finding, when they get 3-D imaging along with a traditional mammogram, according to Rafferty. Previously, about 8 percent of women who were screened for breast cancer at Mass. General had to come in for additional screening, which has declined to less than 6 percent with the addition of 3-D mammography. What’s more, Rafferty said, “our cancer detection rate has gone up by roughly 20 percent.”

Women currently need to have both a standard mammogram and a 3-D image — to get a flat picture of the entire breast as well as a contoured view of various layers — which exposes them to twice as much radiation but is still within the FDA’s acceptable safety range. An FDA expert panel voted in October to approve an add-on to the latest Hologic machines that would re-create a 2-D image using just one X-ray scan.

Massachusetts General Hospital Imaging has acquired 10 of the 3-D imaging machines for its breast center on the main campus and affiliated radiology centers in Waltham, Chelmsford, Danvers, and Worcester. A handful of community hospitals such as Newton-Wellesley and Lowell General have also recently begun to offer the 3-D screening.

Other area teaching hospitals, however, have been slower to adopt the technology, and only about 300 medical institutions nationwide have purchased the device, according to Hologic. That may be related to the cost — $760,000 for the machine and software — and the lack of an insurance code to bill for the additional imaging, which costs $50 per patient beyond standard mammography. Insurers must cover standard mammograms without any copayments.

Some hospitals, including Mass. General, don’t charge women for the extra cost of the screening, while others have been able to get reimbursed by billing under a miscellaneous code. Women, though, sometimes get stuck with a bill for $50 after they’ve had the screening.