False positives decline with breast tomosynthesis

December 19, 2005

Digital breast tomosynthesis promises to dramatically reduce the rate of false-positive mammograms, potentially sparing women from unnecessary follow-up tests and biopsies, according to a study presented at the RSNA meeting.

Digital breast tomosynthesis promises to dramatically reduce the rate of false-positive mammograms, potentially sparing women from unnecessary follow-up tests and biopsies, according to a study presented at the RSNA meeting.

Conventional mammography superimposes layers of breast tissue in a 2D image, a key drawback. This superimposed tissue can hide cancers, yet it can also give the false appearance of cancer, leading to needless recalls and biopsies. DBT is a 3D technique that removes the effect of superimposed tissue.

In a study of 98 patients with abnormal mammograms, DBT as a screening follow-up tool was equivalent or superior to diagnostic mammography in 88% of cases, said Dr. Steven Poplack, an associate professor of diagnostic radiology at Dartmouth Hitchcock Medical Center.

The study group had a total of 112 screening abnormalities. If tomosynthesis had been used as an adjunct to mammographic screening, the recall rate could have been cut by 40%, Poplack said. He was cautiously optimistic in releasing the results, given that the study findings need to be validated in larger trials.

"On the basis of this small study, tomosynthesis is equivalent or superior (to mammography) for diagnosis. It will offer recall reduction and better reflects the reality of the breast, translating into a more accurate diagnosis," he said.

Acquisition time for DBT was 20 seconds and reconstruction time was one minute. Two views were taken in most cases.

Tomosynthesis was superior to diagnostic mammography in 35% of cases, equivalent in 54%, and inferior in 12%. Many of the cases in which tomosynthesis was deemed inferior involved calcifications, and quality may have been affected by the lengthy acquisition time and motion artifact, Poplack said.

Of the total number of potential abnormalities, five were cancers. Three cancers were detected by both mammography and tomosynthesis, and two cases were occult for both techniques.

At the same RSNA session, University of Pennsylvania researchers demonstrated potential for a new technique called contrast-enhanced DBT.

Research shows that neoangiogenesis is essential for breast tumor growth. Due to the nature of vascular networks in a breast tumor, enhancement of breast cancers is different from benign breast tissue.

To date, vascular characteristics of breast cancer have been extensively demonstrated with gadolinium-enhanced breast MR. Drawbacks of MR for this purpose include poor specificity and high expense.

Contrast-enhanced digital mammography has also demonstrated vascular aspects of breast cancer biology, as malignant lesion conspicuity increases with intravenous contrast administration, said Dr Sara Chen, who presented the group's results.

"Work with contrast-enhanced digital breast mammography is promising, but it relies on projection mammographic views, which are inherently limited as they are 2D images of a 3D anatomic structure. Superimposition of nonadjacent overlying breast tissue may unfavorably impact lesion conspicuity, even with lesion contrast administration," Chen said.

DBT reduces the effect of superimposed tissue, making lesions more apparent.

"If tomosynthesis and contrast-enhanced digital mammography could be combined into a single technique, the benefits of both might potentially be integrated," Chen said.

The group performed a pilot study, using modified commercial equipment, to test this theory. The pilot involved 13 women with breast lesions that were BI-RADS category 4 or 5. All patients underwent multimodality breast imaging, including contrast-enhanced DBT. As researchers expected, lesions became more apparent with the combination of digital mammography and tomosynthesis.

"Our initial experience found contrast-enhanced DBT to be a clinically feasible technique that provides us with vascular information about breast lesions qualitatively concordant with that of breast MR. As such, it [the technique] may have potential to visualize vascular characteristics of breast lesions," Chen said.

The group now plans to optimize technical factors, mainly to address problems with motion artifact. Researchers are also developing a dedicated system for contrast-enhanced DBT.

For more online information, visit Diagnostic Imaging's RSNA Webcast.