Impact of material and structural bone properties on 1-MHz velocity measurements in human forearms

The ultrasonic axial transmission technique allows investigation of skeletal sites, such as the cortical layer of long bones (radius, tibia). We investigated, in vitro, the relationships between 1 MHz axial transmission speed of sound (SOS) measurements at the radius and site-matched measurements of cortical thickness (C.TH), intracortical porosity (POR), tissue mineralization (MIN) and BMD (bone mineral density) using synchrotron radiation microtomography. The highest correlations were found between SOS and porosity, mineralization or BMD (R²_SOSPOR/=0.28, p<10^-.3; R²_SOSMIN/=0.38, p<10^-4; R²_SOSBMD/=0.57, p<10^-3). The respective adjusted contributions of intracortical porosity (-24 m/s.%^-1) and tissue mineralization (-3.5 m/s.(mg/cm³)^-1) to SOS values were assessed. These results suggest potential sensitivity of axial transmission SOS to changes in cortical bone status under different pathological conditions or treatments affecting porosity and/or tissue mineralization.