Stereo mammography results impress, but hurdles remain
There still is work to be done, but researchers have concluded an initial clinical trial involving a new stereoscopic digital mammography system that eventually could help radiologists identify more breast cancers with fewer false-positive results.
The system, which was developed by Cambridge, MA-based BBN Technologies and Beaverton, OR-based Planar Systems, acquires two digital images of the breast that are separated by about 8 degrees. A visual system then fuses the images so that the mammographer can view a three-dimensional image from his or her workstation. The approach offers several advantages, but researchers are particularly excited about the system's improved detection power and accuracy.
"The most important finding from the clinical trial was that the false-positive rate could be cut by almost half" over traditional full-field digital mammography (FFDM), explains David Getty, PhD, a division scientist at BBN Technologies who has been working on the system for a dozen years. Getty can't be more specific about the results of the trial because it is not yet clear where and when that data will be published, but he says the results are in line with preliminary data that were unveiled in Chicago at the annual meeting of the Radiological Society of North America in November 2007.
At that time, Getty reported that of 1,093 patients at elevated risk for breast cancer who had undergone both a FFDM exam and a full-field stereoscopic digital exam, 259 suspicious breast lesions were found. Further diagnostic testing showed that 109 were true lesions. However, where FFDM missed 40 of those lesions, the stereoscopic exam missed only 24.
Decrease in false positives
Researchers have shown a 43% decrease in false-positive results with this technique, explains Carl D'Orsi, MD, FACR, the lead investigator of the study and the director of breast imaging at Emory University School of Medicine in Atlanta. "The radiologists were very positive about using the technology and, anecdotally, said it took a shorter time to read [the images] than standard mammography."
Next on Getty's agenda is a study to determine if stereo mammography can yield the same robust results at half the radiation dose.
"In the clinical trial that was just completed, each of the two images comprising a stereo pair was captured at a standard full dose. As a result, the woman getting a mammogram would be getting twice the radiation dose compared to a standard mammogram," says Getty. "We have good reason to believe that we can cut the dose by half for the stereo images, which would result in a total dose to the patient that would be the same as a standard mammogram, and that we won't lose any accuracy in doing that." Getty is in discussions with Fujifilm Medical Systems in Stamford, CT, about beginning this research in the near future.
No regulatory hurdles expected
On the plus side, Getty is not anticipating any significant regulatory hurdles with the system because regulators with the Food and Drug Administration (FDA) have indicated that because the Planar monitors used in the stereo display apparatus already are approved for mammography, agency clearance should necessitate only a variance to that approval.
A bigger hurdle to getting the stereo system into imaging centers may well be hardware limitations. Only a few existing mammography units can be retrofitted with the stereo capability. "The property that the mammography unit has to have to make it possible is independent movement of the X-ray tube from the compression table," explains Getty. While the Senographe mammography unit, developed by GE Healthcare (Waukesha, WI) has this capability, very few of the other FFDM units do, he notes.
Stereo works with DBT
Getty points out, however, that all of the major mammography unit manufacturers are developing digital breast tomosynthesis (DBT) units, which could all easily be adapted to stereo mammography as well since they have independent movement of the X-ray tube and the compression table. In fact, Getty envisions stereo mammography potentially being used in concert with DBT. For example, stereo mammography could be used as a first-line screening exam. If findings needed to be further explored, DBT then could focus in the specific areas of concern that were delineated by stereo mammography.
Such an approach potentially could alleviate one drawback to digital tomosynthesis which is that because it takes multiple images or slices from different angles, interpreting the exam is time consuming. Getty suggests that stereo mammography not only could screen out women who do not need DBT, but it also could narrow down the amount of breast tissue that the radiologist needs to explore with DBT.
"Stereo mammography is perfectly suited to the DBT unit because just as you move the X-ray tube to do DBT, you can also move it just to take the stereo pair [of images]," adds Getty. At press time, the FDA had not yet approved use of a DBT unit for breast cancer screening, but industry experts are anticipating approval of at least one unit soon.
There still is work to be done, but researchers have concluded an initial clinical trial involving a new stereoscopic digital mammography system that eventually could help radiologists identify more breast cancers with fewer false-positive results.You have reached your article limit for the month. Subscribe now to access this article plus other member-only content.
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