Estimation of femoral bone density from trabecular direct wave and cortical guided wave ultrasound velocities measured at the proximal femur in vivo

Abstract

Bone mineral density (BMD) of the proximal femur is a predictor of hip fracture risk. We developed a Quantitative Ultrasound (QUS) scanner for measurements at this site with similar performance (FemUS). In this study we tested if ultrasound velocities of direct waves through trabecular bone and of guided waves through cortical bone could be used to estimate BMD. In two centres, Kiel and Odense, we measured time‐of‐flight (TOF) of waves through the trabecular greater trochanter and cortical intertrochanter as well as a wave through soft tissue only. TOF was adjusted for leg width using ultrasound echoes reflected from the skin of the leg to yield speed‐of‐sound (SOS) of different wave components. Data were cross‐calibrated and pooled (62 women). Bivariate correlations and a multivariate model were calculated for the estimation of femur BMD. BMD correlated both with trabecular and cortical SOS but not soft tissue SOS. Coefficient of determination, percentage residual error (RMSE) and level of significance (p) were R2=0.51, RMSE=12.6%, p<0.0001 for trabecular and R2=0.53, RMSE=12.3%, p<0.0001 for cortical measurements. The combination of trabecular, cortical and soft tissue SOS improved the correlation to R2=0.69, RMSE=10.4%, p<0.0001. Multiwave ultrasound methods allow estimation of femoral BMD with a low residual error.