Ultrasound propagation in cancellous bone: Dependence on mechanical, material, and structural properties

Critical skeletal sites for osteoporotic fractures include femur and vertebrae. However, many ultrasound devices designed for the management of osteoporosis instead target the calcaneus, which is far more accessible to ultrasound than femur or vertebrae. Calcaneus-based devices have been shown to be very effective for predicting osteoporotic fractures of the hip. MicroCT-based finite element models support targeting of calcaneus based on similar biomechanical structure-function relations in calcaneus compared with femoral neck, greater trochanter, proximal tibia, and vertebra. Finite element analysis can be used to relate these mechanical properties to ultrasonic properties such as broadband ultrasound attenuation, speed of sound, and broadband ultrasound backscatter. As an ultrasound beam propagates through cancellous bone, it loses energy to absorption, longitudinal-shear scattering, and longitudinal-longitudinal scattering. The relative roles of these mechanisms can be demonstrated in phantom models.