Anisotropy of ultrasonic backscatter and attenuation from human calcaneus:Implications for relative roles of absorption and scattering in determining attenuation

Although bone sonometry has been demonstrated to be useful in the diagnosis of osteoporosis, much remains to be learned about the processes governing the interactions between ultrasound and bone. In order to investigate these processes, ultrasonic attenuation and backscatter in two orientations were measured in 43 human calcaneal specimens in vitro at 500 kHz. In the medio lateral (ML) orientation, the ultrasound propagation direction is approxima tely perpendicular to the trabecular axes. In the anteroposterior (AP) orie ntation, a wide range of angles between the ultrasound propagation directio n and trabecular axes is encountered. Average attenuation slope was 18% gre ater while average backscatter coefficient was 50% lower in the AP orientat ion compared with the ML orientation. Backscatter coefficient in both orien tations approximately conformed to a cubic dependence on frequency, consist ent with a previously reported model. These results support the idea that a bsorption is a greater component of attenuation than scattering in human ca lcaneal trabecular bone. (C) 2000 Acoustical Society of America. [S0001-496 6(00)03806-6].