Do Women with Low Breast Density Have Regionally High Breast Density?

Average volumetric breast density has been found to be associated with interval cancers. The association is believed to be partly due to mammographic masking. We asked if regional density may be a more sensitive descriptor of masking than average density. In this work, we propose a new method to identify high density regions based on calibrating pixel-level volumetric breast density to Breast Imaging Reporting and Data System (BI-RADS) Version 4 categories. Local breast density was measured using the single-energy X-ray absorptiometry (SXA) technique. In 583 women undergoing screening mammography, we found percent fibroglandular volume ranges that corresponded to each BI-RADS category: 0-4.9 % (BI-RADS 1), 5.0-18.2 % (BI-RADS 2), 18.3-48.9 % (BI-RADS 3) and 49.0-100 % (BI-RADS 4). Women with an average BI-RADS 1 category had 21840 pixels (0.014 mm) breast area considered high density (category 4) compared to 186469 pixels (0.014 mm) in women with average BI-RADS 4 category. We conclude that some women with low breast density still have regions of high density that may mask breast cancers. These scores and localized density colorized maps may better help radiologists in the decision to utilize secondary adjuvant screening than whole breast BI-RADs scores.