Surface Compression Alters in Vivo VisR Stiffness, Viscosity, and Anisotropy Measurements in Human Breast

Viscoelastic response (VisR) ultrasound has been developed by our group to interrogate tissue stiffness and viscosity. VisR has several potential advantages for breast cancer diagnostic imaging such being non-invasive and low-cost. Because ultrasound can penetrate dense breasts more effectively than mammograms, it may improve the detection of malignant masses in women with dense breasts. VisR-based estimates of stiffness, viscosity, and anisotropy have been shown in our preliminary studies to discriminate malignant and benign breast lesions. However, a potential limitation of VisR could be dependence on tissue pre-loading from applied surface compression by the practitioner. We conducted an IRB-approved clinical study of 20 women with no known breast pathologies to assess the impact of compression on VisR measurements of peak displacement (PD), relative elasticity (RE), relative viscosity (RV), and degree of anisotropy (DoA). Participants were between the ages of 30-90, and 10/20 had mammographically dense breasts. We found that surface compression significantly affected measurements of PD, RE, and RV in breast tissue, in vivo. In particular, in women with dense breasts, stiffness (via PD and RE) increased significantly with applied compression. DoA of PD, RE, and RV increased, decreased, or stayed the same with compression. No significant difference was found in DoA with compression between the breast density groups. Based on these findings, we recommend that surface compression be standardized and monitored when using VisR for clinical breast imaging, especially in women with dense breasts. Further studies are needed to identify an optimal strain range for VisR measurement repeatability.