Should broadband ultrasonic attenuation be normalized for the width of the calcaneus?

Broadband ultrasonic attenuation (BUA) is a measure of ultrasound transmission through the calcaneus that is dependent on bone thickness as well as the density of scattering centres. This report examines whether the normalization of BUA (units dB MHz-1) for calcaneal width (nBUA: units dB MHz-1mm-1) improves the discrimination of clinical studies. BUA and calcaneal width were measured in 200 women using a contact ultrasound (CUBA-Research) system and nBUA evaluated by dividing BUA by bone width. 150 subjects were early post-menopausal and the remaining 50 were osteoporotic women with confirmed vertebral crush fracture. The ability of BUA and nBUA to differentiate between the two groups of subjects was compared using receiver operating characteristic (ROC) analysis. The areas (and standard errors) under the ROC curves were 0.878 (0.033) for BUA and 0.910 (0.028) for nBUA. The difference (and standard error) between the areas under the ROC curves was 0.033 (0.026) and was not statistically significant.