A recently developed 3-D imaging technique called stereoscopic digital mammography enables physicians to better visualize abnormal breast tissue
--by Joann Jovinelly
For decades, two-dimensional mammography X-rays defined the way in which physicians detected abnormal legions in breast tissue. Now, a new technology called stereoscopic digital mammography (SDM) holds significant promise to not only make earlier detection of cancer cells possible, but to help radiologists and doctors see legions that would otherwise be masked.
The usefulness of SDM technology lies in its ability to provide doctors with 3-D images that duplicate the natural ways in which the human eye can see. The benefits of such imaging are two-fold: the technique increases accuracy and early detection, and it decreases the number of false positives, saving many women from being called back for follow-up testing, as well as the fear and worry that often accompanies those procedures, including ultrasound testing and tissue biopsy.
“Our eyes see the world from two slightly different perspectives,” says Carl J. D’Orsi, M.D., head of the Department of Radiology and Imaging Sciences at Emory University in Atlanta, one of a few places in the United States where SDM technology is already in place and where research that compared both types of imaging was conducted.
In that study, which appears in this month’s issue of Radiology, SDM imaging was more than three percent more accurate than older 2-D imaging methods; SDM detection rates were 91.2 percent accurate, compared to 87.8 percent for traditional mammograms.
“Standard mammography is widely considered to be one of the most difficult exams to read because legions may be disguised by normal tissue,” D’Orsi says. “At the same time, false-positives can also occur because of the two-dimensional images provided by the existing technology.”
D'Orsi found that it really is all about your perspective.
“In this [SDM] technique, the X-ray tube functions as the eyeball, with two different images providing slightly different views of the internal structure of the breast,” D’Orsi continues. “We found that the stereoscopic technique could significantly decrease the need for calling women back for additional exams.”
D’Orsi and his research team compared SDM imaging to regular 2-D mammograms in 779 patients at elevated risk for developing breast cancer because of personal or family history.
Patients received both tests on a single day and both were evaluated independently. After one year, image findings were compared to follow-up imaging tests and/or biopsy results, noting the near three percent increase in accuracy with SDM.
“In this study we used a high-risk population to get an adequate number of cancers, and we acquired each of the images comprising the stereo pairs with a full standard X-ray dose,” explains D’Orsi. “Now that we know the technique is worthwhile, we’re repeating the study in the general population with a dose comparable to routine screening mammography.”
Stereo mammography techniques, now confined to just a handful of imaging centers around the United States, may eventually be a prevailing technology that increases the early detection of breast cancer cells. As well, SDM imaging will provide more complete visual information to keep physicians from playing it safe by calling women back for repeated, unnecessary image tests.
Dr. David Bluemke, Director of Radiology at the National Institutes of Health Clinical Center and professor of Radiology at Johns Hopkins University, calls SDM imaging a “great advancement” in the field of radiology, but one that falls short. “True 3-D tomographic imaging of the breast is ultimately needed [for the best accuracy],” he explains.
A 2007 study by David J. Getty, Ph.D., that was presented at the Radiological Society of North America also noted the positive results of SDM imaging. More than 1,000 patients with elevated breast cancer risk were screened using both types of mammograms. Out of 259 suspicious findings, 109 were eventually found to be cancerous. In that study, standard mammography tests missed 40 of the 109 cancers, while SDM failed to detect just 24.