Breast tomosynthesis hits workflow, dose obstacles

January 1, 2007

News that two views are better than one with the emerging and promising technology of breast tomosynthesis raises questions about the technique's practicality and cost-effectiveness as a screening tool.

News that two views are better than one with the emerging and promising technology of breast tomosynthesis raises questions about the technique's practicality and cost-effectiveness as a screening tool.

Tomosynthesis is a 3D digital mammographic technique that has been in development since the 1960s. In breast imaging, it minimizes the effects of overlapping tissue, possibly helping to improve sensitivity and specificity relative to conventional mammography.

Researchers at Massachusetts General Hospital in Boston, where the technique originated, released a new study at the RSNA meeting stressing the importance of imaging the breast in both the craniocaudal and mediolateral oblique positions when performing tomosynthesis.

Some tomosynthesis devices involve 10 to 15 separate image acquisitions along an arc, and one model acquires continuously along the arc. The technology has been touted as a technique that acquires information from one view or direction.

It now appears that two separate views, or two arcs, are needed. The tube is positioned lateral to medial and then moved to the craniocaudal direction. This would double the acquisition time and the number of images, as well as make interpretation more time-consuming and require a higher dose.

"The need for two projections does complicate the situation. We will have to look carefully at costs and benefits," said Dr. Daniel Kopans, a professor of radiology at MGH, during a tomosynthesis session at the RSNA meeting.

The MGH study involved 34 women scheduled to undergo biopsy. MLO and CC views were obtained with a Hologic tomosynthesis system at a total dose roughly equivalent to a standard mammogram.

The researchers compared visibility of 34 lesions on the different acquisitions. Both views enabled equally good visualization of 22 lesions. Four lesions were more visible on the MLO view, however, and five were more visible on the CC view. Three lesions were visible only on the CC view, and all of these proved to be malignant.

Researchers at Duke University Medical Center in Durham, NC, which has one of the first installations of the Siemens Medical Systems tomosynthesis prototype, also see the necessity for two views, according to Joseph Lo, Ph.D., an assistant professor of radiology.

"Investigators assumed we could get away with a single scan. As such, we have been willing to use double the dose for the single tomosynthesis view. If we need to do two tomosynthesis views, then we need to think carefully about cutting the dose in half or performing some kind of hybrid scan. For example, we could do a tomosynthesis CC and a mammography MLO, or vice versa," he said.

Some groups are already using the same dose for (two-view) tomosynthesis and mammography, but there is a need to ensure this doesn't result in decreased clinical performance.

At the RSNA meeting, Lo presented positive results with the tomosynthesis prototype in imaging masses in 144 patients.

Researchers assessed sensitivity for lesion detection in 271 breasts. There were 30 lesions, including eight cancers. Mammography picked up 21 of 30 lesions, achieving a 70% sensitivity rate, while tomosynthesis identified 27 lesions, achieving a 90% sensitivity rate.

Tomosynthesis achieved this high sensitivity with a lower callback rate relative to conventional mammography (10% versus 15%), according to Lo.