Comparison of 3D and 2D Breast Density Estimation from Synthetic Ultrasound Tomography Images and Digital Mammograms of Anthropomorphic Software Breast Phantoms

Breast density descriptors were estimated from ultrasound tomography (UST) and digital mammogram (DM) images of 46 anthropomorphic software breast phantoms. Each phantom simulated a 450 ml or 700 ml breast with volumetric percent density (PD) values between 10% and 50%. The UST based volumetric breast density (VBD) estimates were calculated by thresholding the reconstructed UST images. Percent density (PD) values from DM images were estimated interactively by a clinical breast radiologist using Cumulus software. Such obtained UST VBD and Cumulus PD estimates were compared with the ground truth VBD values available from phantoms. The UST VBD values showed a high correlation with the ground truth, as evidenced by the Pearson correlation coefficient of r=0.93. The Cumulus PD values also showed a high correlation with the ground truth (r=0.84), as well as with the UST VBD values (r=0.78). The consistency in measuring the UST VBD and Cumulus PD values was analyzed using the standard error of the estimation by linear regression (sigma(E)). The sigma(E) value for Cumulus PD was 1.5 times higher compared to the UST VBD (6.54 vs. 4.21). The sigma(E) calculated from two repeated Cumulus estimation sessions (sigma(E)=4.66) was comparable with the UST. Potential sources of the observed errors in density measurement are the use of global thresholding and (for Cumulus) the human observer variability. This preliminary study of simulated phantom UST images showed promise for non-invasive estimation of breast density.