Finite-difference time-domain analysis of ultrasound backscattering in cancellous bone

Numerical analysis of ultrasound backscattering in cancellous bone was performed by using three-dimensional finite-difference time-domain (FDTD) simulations with numerical models reconstructed from microcomputed tomographic images of bovine bone. In the simulations, two cancellous bone models with different thicknesses were used. In each model, an artificial absorbing boundary was set at the back surface opposite to the front surface toward which an ultrasound pulse wave was transmitted from a concave transmitter/receiver in water. From the difference between the simulated waveforms for the two bone models, the reflected wave from the front surface could be canceled, and only the backscattered waves inside the bone could be extracted. For the ultrasound transmission parallel to the main orientation of the trabecular network, the backscattered waves from various bone depths were analyzed. The peak-to-peak amplitudes of the backscattered waves from the deep bone depths were moderately correlated with porosity [R² = 0.43-0.54 (P <; 0.001)]. The backscattered waves from the deeper bone depth could be more clearly separated into the fast and slow waves, and the backscattered wave amplitude could be regarded as the slow wave amplitude.