Microstructural anisotropy evaluation in trabecular bone structure using the mode-converted (longitudinal to transverse, L-T) ultrasonic scattering

Abstract

The mode-converted ultrasonic scattering method is utilized to characterize the structural anisotropy of a phantom mimicking trabecular bone, fabricated using metal additive manufacturing from a high resolution CT image of trabecular horse bone. A normal incidence transducer transmits longitudinal waves into the sample, while the scattered transverse signals are received by an oblique incidence transducer. Four L-T measurements are performed by collecting scattering from four directions. The results show that the L-T converted scattering amplitude is highly dependent on the microstructural anisotropy direction. The ratios of L-T converted amplitudes for measurements in different directions is calculated to characterize the anisotropy of sample. The results show that the anisotropy is changing along the sample, which coincides with simulation results previously obtained on the same structures, as well as with the anisotropy estimated using image processing of the CT scans. The anisotropy was shown to increase monotonously along the sample from 0.48 to 0.7 depending on the location. At the same time, the ratio of LT scattering amplitude measured in two perpendicular directions was shown to increase monotonously from 0.6 to 0.67. These results suggest the potential of mode-converted methods to assess the anisotropy of structures including trabecular bone.