In vitro comparative study of three devices based on ultrasonic axial transmission

Abstract

In the axial transmission technique the velocity of waves propagating in the direction of bone axis is used to characterize cortical bone (radius, tibia, etc.). Corresponding clinically used devices are based on a long wavelength approach (typical frequency around 200 kHz) or shorter wavelength (typical frequency around 1 MHz) compared to bone thickness. They differ also by the methods of wave velocity evaluation. The aim of this study is to compare the sensitivity to bone properties of three representative devices using an in vitro investigation of the same specimens coupled with x-ray determination of bone properties. The moderate correlation between velocities suggests an important impact of site-matching. Among higher frequency devices, the one associated to the bidirectional probe provided generally higher correlation with bone properties than conventional axial transmission. The high-frequency devices are less sensitive to cortical thickness, CSA and trabecular BMD than the low-frequency device because high-frequency waves interrogate a thinner cortical layer than low-frequency waves. Our results suggest that different axial transmission approaches reflect different bone properties. Therefore, a multi-frequency technique might be useful in probing different bone properties at the same time (e.g., cortical thickness and BMD).