Characterization of human femoral trabecular bone in vitro using transmission and backscatter ultrasound measurements

We investigated the relationships between ultrasonic properties and bone properties measured on the human proximal femur. Two-dimensional scans in transmission and pulse-echo mode were performed using 1-MHz focused transducers to measure ultrasound parameters: slope of the frequency-dependent attenuation coefficient (nBUA); speed of sound (SOS); broadband ultrasonic backscatter (BUB). BMD (bone mineral density) was determined using X-ray computed tomography (QCT). The microarchitecture was characterized using synchrotron radiation micro-tomography (SR-μCT). All QUS parameters were significantly correlated to BMD (nBUA: R²=0.71; SOS: R²=0.77; BUB: R²=0.51). Multiple regression models were tested with BMD and micro-architecture as independent variables. While most of the variability of QUS parameters measured in transmission (nBUA: R²=0.85; SOS: R²=0.94) could be explained by a combination of structural features, approximately half of the variance of BUB (R²=0.55) remains unexplained. The multivariate model found for BUB was consistent with general ideas of incoherent Rayleigh scattering by small trabecular structures. These results suggest that transmission QUS measurements at the hip may be relevant for fracture risk prediction, whereas random interference noise remains a serious limitation to the precision of backscatter measurements.