Osteoporotic fracture in the proximal femur is a concern for the aging population. Ultrasonic techniques, which are non-invasive and cost-effective, are then attracting attention. To understand wave propagation in the proximal femur, we performed 3-D Finite-Difference Time-Domain (FDTD) simulations using two digital femur models (bone volume to total volume ratio BV/TV of the cancellous parts: 16% and 20%), which were created from CT data of a 73-year-old woman. In the model, the outer cortical bone and trabeculae were assumed to be isotropic, while heterogeneity of density was estimated from the bone mineral density of CT data. A convex array transducer was placed 2 cm from the proximal femur, transmitting a one-cycle sinusoidal wave at 1 MHz. Reflected signals from the ROI, extending from the surface to a depth of 5 mm, were observed at each element of the array. For accurate analysis of the waves, the superposition of waves from the trochanter to femoral head should be carefully considered. However, frequency analysis of the waves revealed strong dispersion around the femoral neck, where scattering from trabeculae was clearly observed through the thin cortical layer. The dispersion was more pronounced in the model with a BV/TV of 20%.
Maeda et al. (2025) studied this question.