Apart from age and gender, high mammographic density is the strongest risk factor for breast cancer. Several studies suggest that elevated breast density is a leading risk factor among younger women.  Mammographic screening is generally not recommended for women until age 40 because breast cancer incidence is low among these women and ionizing radiation itself increases the risk of breast cancer.  Further risk stratification may permit the identification of a previously overlooked sub-group for whom risk is high enough to merit screening or preventative measures.  Risk stratification and pre-menopausal screening would be particularly attractive if achieved using a safe, non-ionizing, inexpensive imaging solution, such as SoftVue. The speed of sound is directly proportional to tissue density. Consequently, one can measure changes in breast density by measuring changes in sound speed. The ability of SoftVue to accurately measure sound speed permits measurement of changes in breast density quickly, safely, and without exposure to ionizing radiation, as demonstrated in our previous publications.  

 The aim of this study was to determine whether SoftVue measurements of breast sound speed could be a viable surrogate for measuring breast density. A total of 92 patients were imaged with SoftVue, yielding volumetric coverage of the breast. Corresponding mammograms were also available. The mammograms and sound speed images were segmented to calculate percent density with the two modalities. A strong positive association between BI-RADS density category (based on mammography) and percent volume density from SoftVue was demonstrated (Spearman r²= 0.69 p<0.001), with significant differences between all BI-RADS categories as assessed by one-way ANOVA and Scheffé post hoc analysis. Furthermore, comparing SoftVue volume percent density to mammographic area percent density yielded a strong correlation with the CC view (r²=0.75), indicating that UST percent density and mammographic percent density are highly correlated. This result supports the conclusion that breast sound speed is an accurate surrogate for breast density.

 A comparative SoftVue-MRI imaging analysis provides additional strong evidence for this conclusion. Percent parenchyma was measured from MRI images and plotted against volumetrically averaged sound speed as measured by SoftVue. The strong correlation between breast sound speed and 3-D percent parenchyma by MRI provides evidence that MRI and SoftVue yield similar estimates of breast density. These observations suggest that SoftVue has the accuracy and volumetric advantages of MRI without the disadvantages of cost (inherently low cost of ultrasound technology and no need for shielding) and lengthy exam times. Therefore, SoftVue offers compelling advantages for risk assessment.