Ultrasound propagation in bone

Abstract

Bone sonometry is a rapidly evolving diagnostic technology for managing osteoporosis. Bone sonometers that measure ultrasound propagation through calcaneus or along long bones (parallel to the long axis) have been used for many years. However, the Food and Drug Administration recently cleared two new, innovative designs that measure ultrasound propagation perpendicular to long axes of tibia (2016) and radius (2017). A basic understanding of wave propagation in bone is required in order to compare devices based on different physical principles and skeletal sites. Phantom studies elucidate the relative importance of components of signal loss during propagation through bone: absorption, longitudinal-to-shear scattering, and longitudinal-to-longitudinal scattering (Wear, IEEE Trans. UFFC, 55, 2418–2425, 2008). Comparison of experimentally-measured ultrasound properties (attenuation, sound speed, and backscatter coefficient) and finite-element-analysis-derived mechanical properties in vitro (n = 25) indicate that ultrasound measurements provide additional information regarding fracture risk beyond that provided by bone quantity alone (Wear et al., Bone, 103, 93–101, 2017). Bone can support two longitudinal waves, which often overlap in time and frequency domains but can be separated using Bayesian probability theory or the modified least-squares Prony’s (MLSP) method (Wear et al., J. Acoust. Soc. Am., 136, 2015–2024, 2014).