Frequency dependence of ultrasonic attenuation in bovine cortical bone: an in vitro study

Recent progress in quantitative ultrasonic (QUS) techniques enables the in vivo evaluation of cortical bone, which is determinant in bone fragility. However, the interaction between ultrasound and cortical bone remains poorly understood. Most ultrasonic studies have been confined to longitudinal wave speed analysis and the frequency dependence of ultrasonic wave attenuation in this complex multiscale structure has not been extensively investigated. Our objective was to evaluate in vitro the frequency dependence of attenuation in bovine femoral cortical bone samples obtained from three specimens at different anatomical locations along the diaphysis axis and around the circumference. The frequency-dependent attenuation coefficient was evaluated after correction of transmission effects using a transmission device operating at 10 MHz. Attenuation exhibits a non linear variation versus frequency. However, the quasi-linearity of attenuation on a 1 MHz restricted bandwidth around 4 MHz enables broadband ultrasonic attenuation (BUA) evaluation. Our study demonstrates the feasibility of BUA measurements in the three directions (axial, radial and tangential) with reasonable precision (standardized coefficient of variation: 10% to 12%). Significant differences in BUA are obtained according to the anatomical location. BUA values are higher in the distal and proximal parts of the bone than in the midshaft and in the posterior and lateral parts than in the medial and anterior parts. Findings are consistent with results previously obtained and may be explained primarily by scattering phenomena but also by bone viscoelasticity.