Microdamage evaluation in human trabecular bone using non-linear ultrasound

The primary aim of this work is to investigate the potential of nonlinear ultrasound for micro-damage detection in human bone. Micro-damage evaluation in human bone is important because it characterizes fracture risk. Experiments were carried out in human femoral specimens with marrow and soft tissues removed. An ultrasound wave was modulated by using low-frequency vibrations applied directly to the bone specimens. The modulation of the ultrasound appears in the form of side frequencies around the fundamental high frequency, corresponding to low frequency vibration. The specimens were subjected to progressive damage accumulation and the nonlinear modulation was measured. It was shown that the modulation amplitude increases with increasing micro-damage and can be therefore, used as a measure of damage. The obtained results indicate that, in contrast to conventionally considered hysteric nonlinearity, dissipative acoustic nonlinearity may also play significant role for the observed nonlinear modulation effects. The proposed technique is superior compared to Nonlinear Resonance Ultrasound Spectroscopy (NRUS) because the size and the shape of samples are not important. Furthermore, the method is noninvasive, easy to implement and most important, can be proved appropriate for in vivo bone damage characterization.