Imaging ultrasonometry of the calcaneus: Dependence on calcaneal area

The purpose of this study was (1) to investigate the dependence of broadband ultrasound attenuation (BUA) and speed of sound (SOS) measured in a circular region of interest (ROI) having a fixed size on calcaneal area and (2) to examine whether the normalization of ultrasonic variables for the area of the calcaneus provides better differentiation of diseased subjects from healthy individuals. Ultrasound variables were estimated in 169 healthy postmenopausal women (mean age 66.5 years, range 42-87 years) and 39 women with vertebral fractures (mean age 72.9 years, range 51-86 years). A minimum attenuation ROI, 15 mm in diameter, with a commercial imaging ultrasonometer was used. Significant relationships were found between both ultrasonic variables and calcaneal area (r(2) = 0.06, P < 0.001 for BUA, r(2) = 0.12, P < 0.0001 for SOS). Normalization of ultrasound variables (BUAn and SOSn) was based on the regression equations of the relationships among BUA, SOS, and calcaneal area. In a precision study, nine women were examined five times each to determine the errors arising from both the repositioning of the foot and selection of the calcaneal area. The reproducibility errors of BUA. SOS, BUAn, SOSn, and area were 0.87%, 0.20%, 1.07%, 0.27%, and 3.72%, respectively. Significant differences were found between the areas under the ROC curve for BUAn and BUA (area under the curve = 0.93 for BUAn versus 0.90 for BUA, P = 0.003) as well as for SOSn and SOS (area under the curve = 0.85 for SOSn versus 0.79 for SOS, P = 0.003). Normalization of ultrasound variables for calcaneal area improves the discrimination of clinical studies.