Transmission scanning acoustic imaging of human cortical bone and relation with the microstructure

To investigate and compare the spatial distribution of velocity with that of the microstructural properties (dimension of the haversian canal, percentage of porosity) on cross section of cortical bone.

Experimental investigations permitted to quantify variation of acoustic properties related with that of the microstructural properties.

Transmission ultrasonic techniques have been used in vitro and in vivo to assess the elastic and acoustic properties of Human bone, but few investigated the relationship between their variation with that of the microstructure.

Two scanning techniques (in transmission with a focused transducer at 5 MHz and an environmental scanning electronic microscope at 20 KV) enabled to obtain the spatial distribution of relative acoustic velocities and the microstructural properties (pore size and porosity).

Increase of the velocities is related with the decrease of pore size and porosity. Around the periphery of the sections, the velocities were found to be significantly lower in the posterior side with a significant increase along the length. Radial variations are correlated to the spatial distribution of the microstructure where the endocortical region is more porous compared to the periosteal region.

Significant alterations of the microstructural properties of the cortical bone reflect small variation of velocity suggesting that the velocities are not so sensitive to microstructural changes.

These results are of importance for the clinicians and researchers to get a better understanding (advantages and limitation) of the use of ultrasound technique to assess material and structural properties of cortical bone. Our study suggested that velocity could be an index of porosity. Then it would be of interest to improve the clinical assessment of bone quality by describing bone both by a mineralization index and a microstructural index.