Ultrasound Tomography Evaluation of Breast Density

Objectives Ultrasound tomography (UST) is an emerging whole-breast 3-dimensional imaging technique that obtains quantitative tomograms of speed of sound of the entire breast. The imaged parameter is the speed of sound which is used as a surrogate measure of density at each voxel and holds promise as a method to evaluate breast density without ionizing radiation. This study evaluated the technique of UST and compared whole-breast volume averaged speed of sound (VASS) with MR percent water content from noncontrast magnetic resonance imaging (MRI). Materials and Methods Forty-three healthy female volunteers (median age, 40 years; range, 29-59 years) underwent bilateral breast UST and MRI using a 2-point Dixon technique. Reproducibility of VASS was evaluated using Bland-Altman analysis. Volume averaged speed of sound and MR percent water were evaluated and compared using Pearson correlation coefficient. Results The mean standard deviation VASS measurement was 1463 +/- 29 m s(-1) (range, 1434-1542 m s(-1)). There was high similarity between right (1464 +/- 30 m s(-1)) and left (1462 +/- 28 m s(-1)) breasts (P = 0.113) (intraclass correlation coefficient, 0.98). Mean MR percent water content was 35.7% +/- 14.7% (range, 13.2%-75.3%), with small but significant differences between right and left breasts (36.3% +/- 14.9% and 35.1% +/- 14.7%, respectively; P = 0.004). There was a very strong correlation between VASS and MR percent water density (r(2) = 0.96, P < 0.0001). Conclusions Ultrasound tomography holds promise as a reliable and reproducible 3-dimensional technique to provide a surrogate measure of breast density and correlates strongly with MR percent water content.