Numerical analysis of backscatter properties of fast and slow waves in cancellous bone

Fast and slow waves can propagate mainly in the trabecular and pore parts of cancellous bone, respectively. Their backscatter properties were numerically analyzed by finite-difference time-domain simulations. Numerical bone models, in which artificial absorbing layers were set at the back surfaces, were prepared, and an ultrasound pulse wave was transmitted from the front surface parallel to the main trabecular orientation. Only the backscattered waves were succeeded to isolate by differencing between two simulated waveforms obtained using the bone models with different thicknesses. The backscatter coefficients, which were the amplitude ratios of the backscattered waves to the incident waves, of the fast wave were not significantly correlated with porosity and mean intercept lengths (MILs) (R2 ≤ 0.29). However, the backscatter coefficients of the slow wave were significantly correlated with porosity (R2 = 0.45-0.67) and MIL of the pore part in the ultrasound direction (R2 = 0.64-0.80).