An in vivo breast tissue backscatter study with 7.5 MHz and 10 MHz probes

Presents the results to date of an on-going study of the backscatter coefficient (BSC) of fibroglandular breast tissue in vivo from 5-13 MHz. The authors compare their findings to published values for this tissue. They also discuss the implications of these findings for the ultrasound visualization of microcalcifications, an important mammographic indicator, within fibroglandular tissue, in which the majority of cancers arise. The authors´ backscatter study is based on the reference phantom method, and utilizes 7.5 and 10 MHz broadband transducers and a commercial scanner. Summed radio frequency echo data have been collected at a series of locations in the left breasts of 14 subjects, age 46-84. This cohort included patients having concurrent clinical ultrasound exams as well as volunteers who were at the center for routine mammography. Care was taken during data collection to avoid saturation in the scanner electronics. Regions of interest (ROIs) in the fibroglandular tissue were subsequently identified among these data and the overlying tissues segmented to compensate for attenuation. The absolute backscatter coefficient and the backscatter frequency dependence were ratiometrically estimated by comparing these ROIs to matched regions in a custom-built phantom calibrated for backscatter and attenuation. The mean coefficients and frequency dependencies found to date are 0.59 f^2.5×10^-3/cm-sr at 7.5 MHz (N _ROI=38, N=11), and 0.075 f^3.2×10^-3/cm-sr (N_ROI=18, N=9) at 10 MHz. These numbers are higher than some published values based on excised breast tissues, which is consistent with the reduction in backscatter found in other tissues as a function of time after excision