Dedicated breast MR boosts accuracy

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Use of a dedicated 1.5T breast MR system may overcome shortcomings of conventional breast MR such as lack of specificity and relatively high false positive and recall rates, according to a study published online Aug. 24 in Radiology. The improved negative predictive value of these systems also may reduce further testing and costs and may obviate biopsy in some cases.

Although breast MR is highly sensitive for breast cancer, it has been hampered by false negatives, particularly in cases of ductal carcinoma in situ (DCIS) and lobular carcinoma, as well as false positives that can lead to additional testing and biopsy.

Bruce J. Hillman, MD, of the American College of Radiology's Image Metrix in Philadelphia, and colleagues hypothesized that a dedicated 1.5T breast MR system with improved spatial and contrast resolution would provide improved morphologic characterization, which would reduce false-positive and false-negative findings compared with conventional whole-body MR systems.

The researchers completed a retrospective analysis of 347 consecutive screening and 587 diagnostic dedicated breast MR exams acquired from April 2006 to December 2007 in women aged 25 to 89 years old at four sites. Results were compared with ground truth (biopsy for cancer and one-year follow up with negative results for negative findings).

The sensitivity for dedicated breast MR was 92 percent, and specificity was 88.1 percent. Negative predictive value was 98.9 percent for all cases. The false-positive rate was 11.2 percent for all cases, and 4.9 percent among screening cases. Hillman and colleagues noted that these metrics outperform historical metrics for conventional breast MR.

“Investigators in many MR studies report a lower diagnostic capability for in situ carcinoma, which is most often depicted as nonmasslike enhancement,” wrote Hillman and his colleagues. “Low-grade DCIS is often missed at breast MR imaging; however, in our study, six of 23 of DCIS cases were low grade and five of 23 cases were intermediate grade.”

The higher negative predictive value of dedicated breast MR vs. whole-body MR could obviate biopsy in some cases, continued the researchers. They also emphasized the increased patient care costs stemming from the low specificity of conventional breast MR, as results could spur redundant testing and unnecessary biopsies. Hillman et al attributed the reduced false-positive rate to “a better ability to discern benign enhancement from truly malignant enhancement as a result of better spatial and contrast resolution in the dedicated system.”

Ultimately, the use of a dedicated breast MR is associated with low risk of patient harm for both screening and diagnostic patients, owing to its low rates of false-positive and false-negative findings, according to the researchers.