Mechanisms of Ultrasonic Attenuation in Porous Bone

Abstract

Ultrasound is a well established method for measuring the density of porous bone. Ultrasonic backscatter is one application of this technology. Backscattered power has been found to decrease with bone density. We hypothesized that increased attenuation causes a decrease in the backscattered power. There are two mechanisms of attenuation in porous bone: absorption and scattering of acoustic energy away from the forward direction. To determine the dominant mechanism for attenuation, we measured eight specimens of human and bovine bone ranging in density from 0.142-0.259 g/cc. Measurements were first performed with the specimens in water (with water filling the porous regions) and then in ethanol. By altering the saturating fluid, we altered the scattering properties of the bone, but not the absorption properties. We observed differences in the backscattered signals between water and ethanol measurement trials, but not between attenuation signals. This suggests that the dominant mechanism of attenuation is absorption.