For decades, breast imaging has pivoted around one gold-standard technology—mammography. Although it is the standard in breast cancer detection, mammography is far from perfect. “Mammography is saving lives. The breast cancer mortality rate is down 25 percent since 1990, primarily because of early detection,” says Daniel Kopans, MD, director of breast imaging at Massachusetts General Hospital (MGH) in Boston. But the downsides to mammography are significant. The false-negative rate hovers in the 20 percent range; false-positives sit at 12 percent, and a radiologist cannot distinguish malignant and benign breast tissue by viewing a mammogram. Consequently, researchers are pursuing a number of avenues to improve the breast cancer detection process via mammography.
One technology close to the verge of reality is expected to address mammography’s shortcomings: breast tomosynthesis. GE Healthcare, Siemens Medical Solutions and Hologic, Inc. are developing breast tomosynthesis systems, and it’s likely that at least one vendor will receive Food and Drug Administration (FDA) approval in the next year, Kopans notes. As researchers demonstrate the promise of breast tomosynthesis, Health Imaging & IT offers a primer on the technology to help sites prep for the next wave of breast imaging technology.
A new view
Digital tomosynthesis acquires multiple projections of a compressed breast from different angles. Images are reconstructed and can be viewed individually or dynamically. The new and improved images address many of the problems associated with conventional mammography.
“Part of the problem with mammographic images is that the breast gets in the way,” says Kopans. That is, breast tissue can obscure malignancies. In some mammographic images, normal tissue can appear suspicious, setting off a chain of additional imaging and patient anxiety. False-positives cost money, impact workflow and frustrate patients and physicians. “Tomosynthesis eliminates problems caused by the superimposition of normal structures,” Kopans says. Tissue isn’t sandwiched; it can be viewed layer by layer, much like the slices of a multidetector CT or MRI study.
The ability to view tissue layer by layer translates into important benefits, says Liane Philpotts, MD, chief of breast imaging at Yale New Haven Hospital in New Haven, Conn. Most importantly, the ability to view individual layers is expected to reduce the callback rate because the radiologist’s view of any suspicious area is not obscured by breast tissue. In addition, radiologists should be able to detect more cancers, specifically those obscured (and missed) by overlapping tissue. Earlier detection is another strong possibility. “It is likely that radiologists will find more smaller cancers than they would with conventional mammograms,” says Philpotts.
Over the last few years, Kopans and his colleagues at MGH have imaged 3,500 women with breast tomosynthesis and compared the findings to 2D mammography. The callback rate is reduced by 30 to 40 percent with tomosynthesis, mainly because tomosynthesis eliminates superimposition of the breast. Breast tomosynthesis also delivers image quality improvements. “Radiologists can see the margins of abnormalities with greater clarity,” says Kopans. Because cancers tend to be ill-defined masses and may have spiculations, clearer margins can help radiologists differentiate benign and malignant findings. Finally, tomosynthesis’ slices allows radiologists to see the exact location of an abnormality. “Breast tomosynthesis will be a great improvement over 2D mammography,” sums Kopans.
Breast tomosynthesis in practice
It’s fair to say that many radiologists’ heads are still swimming after adjusting (or considering the shift) from analog to digital mammography. Is tomosynthesis another major paradigm shift? Is it affordable? What does it mean for workflow?
It appears likely that tomosynthesis will be an easier—and could be a relatively affordable—transition. “Tomosynthesis images look like mammograms, but allow radiologists to scroll through the breast tissue. It’s similar to breast MRI,” says Philpotts. Because most radiologists have grown accustomed to 3D views in other modalities, the learning curve should be relatively short.
The workflow impact of breast tomosynthesis remains unclear. It takes Kopans about 40 seconds to review a breast tomosynthesis study, about the same amount of time as a mammogram. Philpotts provides a longer rough estimate, placing