Measurement of anisotropic elasticity of cortical bone with resonant ultrasound spectroscopy

Overview & Synopsis

Resonant Ultrasound Spectroscopy (RUS) is a method able to precisely characterise all the terms of the stiffness tensor of an anisotropic material from a single measurement of the mechanical resonant frequencies of a sample. A previous attempt to apply this method to bone was unsuccessful due to high mechanical damping of bone which causes resonance peaks to overlap. We built a custom RUS setup and applied a signal processing method which allows retrieving resonant frequencies even in the case of strong peak overlapping. We have tested the system by measuring a sample (about 4*7*8 mm^3) of fiber composite material which is a good substitute for bone in terms of elasticity (anisotropy) and attenuation. Despite the strong damping, we were able to recover 13 different resonant frequencies among the 20 first frequencies predicted by the theory. The elastic coefficients estimated from the measured resonant frequencies were confirmed by time-of-flight elasticity measurement performed in the principal direction of the sample. These results indicate that it should be possible to fully and precisely characterize the elasticity of small cortical bone specimens with a RUS system.