TH-E-L100J-07: Comparison of Mammographic Percent Density and Volumetric Percent Density Determined From Ultrasound Tomography Images

Purpose: Previous ultrasoundtomography work conducted by our group showed a direct correlation between measuredsound speed and physical density in vitro, and increased in vivosound speed with increasing mammographic density, a known risk factor for breast cancer. Building on these empirical results, we investigated the use of volumetric ultrasound percent density (USPD) for breast density estimation. Method and Materials: A breast phantom comprised of fat inclusions embedded in fibroglandular tissue was scanned four times with both ultrasoundtomography and CT. The coronal transmission tomograms and corresponding CTimages were analyzed using a semi‐automatic segmentation routine. Next, a cohort of ∼100 patients was imaged encompassing the entire breast volume (50–75 tomograms/patient). USPD was determined by segmenting high sound speed areas from each slice using a k‐means clustering routine, integrating these results over the entire breast, and dividing by total breast area. USPD was evaluated using two mammographic density measures: (1) qualitative, as determined by a radiologist's visual assessment using BI‐RADS Criteria and (2) quantitative, via digitization and semi‐automatic segmentation of craniocaudal and medio‐lateral oblique mammograms.Results: The integrated areas of the phantom's fat inclusions were compared using both transmission ultrasound and CT for four repeated scans. The average variability for inclusion segmentation was ∼2% and ∼10%, respectively, and a close correlation was observed in the integrated areas between the two modalities. A strong positive association between BI‐RADS category and USPD was demonstrated. Furthermore, comparing USPD to calculated mammographic density yielded moderate to strong positive associations (Pearson r = 0.76–0.84) for MLO and CC views, respectively. Conclusion: These results support the hypothesis that utilizing USPD as an analogue to mammographic breast density is feasible. USPD has the potential to provide a non‐ionizing, whole‐breast analysis of breast density, which may better elucidate the relationship between breast density and breast cancer risk.