Ex-vivo measurements of quantitative ultrasound and micro-CT parameters on intact human femoral heads

The purpose of this work was to study the relationships between quantitative ultrasound (QUS) parameters and the microstructure properties of human proximal femur samples. QUS data acquisition was achieved by means of a custom-developed experimental set-up, which allowed the insonification of excised femoral heads along 30 different directions, each time including both the trabecular region and the cortical layer in their physiologic morphological configuration. Two QUS parameters, Integrated Reflection Coefficient (IRC) and Apparent Integrated Backscatter (AIB), were measured by means of both single-element transducers at two different frequencies (2.25 MHz and 3.5 MHz) and a clinically-available 128-element convex probe. The obtained data were compared with local structural properties of the bone samples as quantified by high-resolution micro-computed tomography (micro-CT). The corresponding results showed a strong correlation between trabecular bone volume fraction and AIB (|r| up to 0.81) and an appreciable linear correlation between cortical bone density and IRC (|r| up to 0.59). QUS parameter values measured by single-element transducers were optimally reproduced when the clinically-available probe was employed. This provides the proposed approach with an interesting potential for a prompt clinical translation as a possible new tool for osteoporosis diagnosis, especially considering that the insonification of the whole femoral head was performed in its physiological shape with all its components (cartilage, cortical layer, trabecular region).