Backscatter techniques are being developed to detect changes in cancellous bone caused by osteoporosis. Cancellous bone is a highly porous, mineralized tissue surrounded by an outer cortex of bone that is much less porous. The cortex produces reflection and attenuation losses that cause errors in the measured backscatter power from cancellous bone. Several techniques have been developed to minimize such errors. The goal of this study was to test two parameters based on a backscatter difference technique: the normalized mean of the backscatter difference (nMBD) and the normalized backscatter amplitude ratio (nBAR). Eleven specimens of human bone were prepared from the femoral neck, a common site for osteoporotic fracture. Backscatter measurements were performed on the specimens with and without the cortex situated between the transducer and ultrasonic region of interest in cancellous bone. The cortex produced a 16% difference in nMBD and a 7% difference in nBAR on average. The difference was not significant in 5 of 11 specimens for nMBD and 7 of 11 specimens for nBAR, indicating that errors caused by the outer bone cortex do not affect either parameter strongly.
Pallera et al. (Wed,) studied this question.