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"Standard mammography is one of the most difficult radiographic exams tointerpret," said David J. Getty, Ph.D., division scientist at BBN Technologiesof Cambridge, Mass. "In a two-dimensional image of the breast, subtle lesionsmay be masked by underlying or overlying normal tissue and thus be missed, andnormal tissue scattered at different depths can align to mimic a lesion,leading to false-positive detections."
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Stereoscopic digital mammography consists of two digital x-ray images ofthe breast acquired from two different points of view separated by about eightdegrees. When the images are viewed on a stereo display workstation, theradiologist is able to see the internal structure of the breast in threedimensions. In the ongoing clinical trial, researchers use a full-fielddigital mammography unit modified to take stereo pairs of images. Theworkstation enables the mammographer to fuse the stereo image pair and to viewthe breast in depth.
"Stereo viewing is the only way to see the structure within the breastvolume in true depth," said Dr. Getty, who has been working on the developmentof the technology over the past 12 years.
As of July 2007, 1,093 patients at elevated risk for developing breastcancer were enrolled in the trial. Each patient received a full-field,standard digital mammography screening examination and a full-field,stereoscopic digital exam, which were then read independently by differentradiologists.
A total of 259 suspicious findings were detected by the combinedmammography procedures and were referred for additional diagnostic testing,including biopsy when indicated. Of those, 109 were determined to be truelesions. Standard mammography missed 40 of the 109 lesions while thestereoscopic exam failed to detect 24.
"Our early results suggest that stereo digital mammography couldcontribute to the earlier detection of cancer," Dr. Getty said. "A smallpercentage of the additional lesions missed by standard mammography butdetected by stereoscopic mammography will turn out to be cancerous."
Of the 259 findings, 150 were false positives, meaning further testingrevealed that no abnormality was present. Standard mammography yielded103 false positives; stereo mammography yielded 53.
"In our study, stereo digital mammography reduced false positives by49 percent," said Dr. Getty. "This could have a significant impact by cuttingin half the number of women who are needlessly recalled for additionaldiagnostic work-ups, resulting in a large savings in cost and patientanxiety."
By the end of the clinical trial this December, a total of 1,500 women atelevated risk of developing breast cancer will have received both the stereoand standard digital mammography screening exams.
According to Dr. Getty, offering wide-scale stereoscopic digitalmammography would entail minor changes to digital mammography equipment andsoftware.
Co-authors of the paper are C.J. D'Orsi, M.D., R.M. Pickett, Ph.D., M.S.Newell, M.D., K.R. Gundry, M.D., S.F. Roberson, M.D., S.R. Bates, M.D., et al.
Dr. Getty is employed by BBN Technologies. BBN Technologies and PlanarSystems developed the stereo display workstation used in the trial.
Note: Copies of RSNA 2007 news releases and electronic images will beavailable online at RSNA.org/press07 beginning Monday, Nov. 26.
RSNA is an association of more than 41,000 radiologists, radiationoncolo