Characterization of the trabecular bone structure using frequency modulated ultrasound pulse.

The objective of this study was to investigate the efficacy of modulated ultrasound signals in the measurement of bone properties as an early indicator of osteoporosis. Twenty-one trabecular bone cubes were harvested from sheep femoral condyles and the cube axes corresponded to the anatomic superior-inferior (SI), antero-posterior (AP), and medio-lateral (ML) orientations. Micro-CT measurements were made on those samples to obtain bone volume fraction (BV/TV), trabecular thickness (Tb.Th), and trabecular separation (Tb.Sp). Ultrasound tests were performed in the three orthogonal orientations using pulse and frequency modulated ultrasound. The comparison of the frequency modulated attenuation (FMA) with the broadband ultrasound attenuation (BUA) was made within the frequency band between 300 and 700 kHz. Results showed that FMA demonstrated higher correlations to the trabecular structure properties in the SI orientation (R(2)=0.84 for BV/TV, R(2)=0.77 for Tb.Th, R(2)=0.7 for Tb.Sp) than BUA (R(2)=0.30 for BV/TV, R(2)=0.27 for Tb.Th, R(2)=0.33 for Tb.Sp). In the AP orientation, FMA had higher correlation to Tr.Sp (R(2)=0.64) than BUA (R(2)=0.48), and relatively lower correlation to BV/TV (R(2)=0.48) and Tb.Th (R(2)=0.31) than BUA (R(2)=0.64 for BV/TV and R(2)=0.58 for Tb.Th). The results suggested that FMA could be a new ultrasound index for bone properties assessment.