Objective: To determine the accuracy of ultrasonic (US) assessment of breast density vs mammography, and its interobserver reliability.
Methods: One hundred consecutive adult women were scanned using a high-frequency ultrasound transducer in the upper outer quadrant of a single breast. Breast density was recorded as one of four categories: < 25%, 25–50%, 50–75%, and > 75% by two radiologists. Digital mammography was performed on the same day and density was assigned to one of four breast imaging-reporting and data system (BI-RADS) categories by a third radiologist. Cohen's Kappa was used to compute inter-rater reliability for US assessment and intermodality agreement among mammographic and US density.
Results: The most frequent mammographic density group was ACR B (43%). US density category B had the highest frequency of readings (49% and 51% readings of radiologists 1 and 2, respectively). Excellent interobserver agreement was seen for the measurements of US density; k = 0.968 [95% confidence interval (CI): 0.925–1]. Substantial intermodality agreement was seen for both radiologists 1 and 2; k = 0.675 (95% CI: 0.552–0.798) and 0.673 (95% CI: 0.551–0.796) respectively (p < 0.001). The US overestimated breast density in 14.5%, while underestimation was seen in 6.5% of cases.
Conclusion: The US provides accurate and reproducible estimates of breast density. This enables personalized screening, particularly in young women and high-density breasts.
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