Evaluation of axially transmitted shear waves in cortical bone: Experimental and simulation study

Abstract

Quantitative ultrasound has become a useful technique for bone assessment. Axial transmission technique has demonstrated various advantages over the through-transmission technique. Longitudinal wave and Lamb modes measurements in bone have been extensively reported while shear waves have been neglected. Shear wave velocities are lower than longitudinal wave velocities and can be useful for bone torsional strength characterization. In this study, plate samples were fabricated from bovine cortical bone. An ultrasonic pulse was transmitted along the long axis of the sample and shear waves were experimentally detected in the MHz range. Using time-of-flight technique, velocities were determined considering three different points of the received wave as a function of the ultrasound incident angle, transmitter-receiver distance and bone plate thickness. The observed shear wave velocities varied in a range (1630 to 1860 m/s) depending on the incident angle and the particular wave path, due to the anisotropy and heterogeneity of the bone structure. A 2D simulation using FDTD method was developed to understand the wave propagation phenomenon. Experimental and simulation results showed good agreement respect to the shear wave velocity estimated in a through-transmission measurement (1720 m/s), specially in angles close to the critical angle (60°).