Impact of a multi-frequency sequence of measurements on first arriving signal velocity on a bone plate model

In several clinical studies, the velocity of the first arriving signal (FAS) measured in axial transmission on various skeletal sites was shown to be a robust ultrasound parameter able to discriminate a population of fractured subjects from healthy subjects. The FAS velocity was measured from time marker (extremum, zero crossing...) and the excitation signal was usually a short impulse with a large frequency bandwidth, allowing a single FAS velocity per bone site. In addition, previous numerical models exhibited variation of the FAS velocity as a function of thickness-to-wavelength ratio with a varying sensitivity to structural and elastic properties of bone. Therefore, a multi-frequency sequence of measurements for a unique bone site may enhance the diagnostic capabilities of the FAS velocities and potentially participate to bone characterization, i.e. to recover structural and/or elastic bone properties from a set of experimental FAS velocities for the same bone site. We report here on predictions of the FAS velocity when excitation frequency varies while bone thickness and material are kept fixed.