Relative contributions of porosity and mineralized matrix properties to the bulk axial ultrasonic wave velocity in human cortical bone

► Bulk wave velocity measured with quantitative ultrasound (QUS) reflects bone quality. ► We measured velocity at 5MHz, matrix impedance and porosity in four human samples. ► Impedance is a surrogate of the mineralized matrix elasticity. ► Variations of porosity and impedance had comparable effects on velocity variations. ► QUS is sensitive to differences in porosity and matrix elasticity among individuals. Velocity of ultrasound waves has proved to be a useful indicator of bone biomechanical competence. A detailed understanding of the dependence of ultrasound parameters such as velocity on bone characteristics is a key to the development of bone quantitative ultrasound (QUS). The objective of this study is to investigate the relative contributions of porosity and mineralized matrix properties to the bulk compressional wave velocity (BCV) along the long bone axis. Cross-sectional slabs from the diaphysis of four human femurs were included in the study. Seven regions of interest (ROIs) were selected in each slab. BCV was measured in through-transmission at 5MHz. Impedance of the mineralized matrix (Zm) and porosity (Por) were obtained from 50MHz scanning acoustic microscopy. Por and Zm had comparable effects on BCV along the bone axis (R=−0.57 and R=0.72, respectively).