Variation of human cancellous bone ultrasonic properties with density and micro-structure

The present study was designed to investigate the relationships between ultrasonic properties, density and micro-architecture of cancellous bone. The slope of the frequency-dependent attenuation coefficient, the speed of sound and the frequency-averaged backscatter coefficient were measured in 25 cylindrical cancellous bone cores. Bone mineral density was determined using X-ray quantitative computed tomography. Microarchitecture was investigated with synchrotron radiation with an isotropic spatial resolution of 10 μm. Several microstructural parameters reflecting the morphology, the connectivity and the anisotropy of the specimens were derived from the reconstructed 3D micro-architecture. The association of the ultrasonic variables with density and micro-architecture was assessed using simple and multivariate linear regression techniques. Variables directly reflecting the amount of bone tissue explained most of the variance of the ultrasonic properties (r² ranging from 70% to 80%) and the additional variance explained by microstructural parameters was small (Δr²<6% at best). In particular, no significant independent association existed between microstructure and backscatter coefficient (a micro-structure related ultrasonic parameter) after adjustment for density. These results may be attributed to the strong covariance effect between micro-architecture and density