P5A-8 Spatial Distribution of Acoustic Impedance and Microstructure Assessed by Scanning Acoustic Microscopy in Human Radial Cortical Bone

A 50-MHz quantitative scanning acoustic microscope (23 mum lateral resolution) has been used to assess spatial distribution of tissue acoustic impedance Z and microstructure features of cortical bone of human radii with the aim to determine, if these parameters vary in the different regions of the cortex. Ten fresh bone specimens taken from diaphyses of 10 human radii were explored. Z and microstructural features related to cortical porosity were derived from the morphometric analysis of the segmented Z images. Regional distributions of tissue acoustic impedance and microstructural features were analyzed along the circumferential and across the radial directions of the entire transverse cross-section of the radius. A higher porosity was found in the inner cortical layer (Mean plusmn SD = 8.9 plusmn 2.3%) compared to the peripheral layer (2.7 plusmn 1.5%) (p<10^-5). ANOVA showed that all the variance can be explained by the regional effect (no statistically significant between-sample variability). Similar to porosity, the number and diameter of pores were greater in the inner layer. In contrast to porosity, ANOVA showed that Z variability can mostly be explained by between-specimen variability. Z in the inner portion (8.25 plusmn 0.4 Mrayl) was significantly higher than in the peripheral layer (8.0 plusmn 0.5 Mrayl) (p < 10^-4). No correlation was found between Z and microstructure. Scanning acoustic microscopy is a valuable tool to provide data on the spatial distributions of microstructural and microelastic bone properties that is useful to improve our understanding of bone structure-function relationships.