Ultrasound surgery monitoring using vibroacoustography-a simulation study

Similar to other therapeutic methods, ultrasound surgery requires an imaging modality to monitor the extent of tissue damage during treatment. Currently, MRI is considered the gold standard method for monitoring tissue ablation, but it is considered to be costly and restrictive in its applications. In this paper, we considered the method of ultrasound-stimulated acoustic emission that uses two ultrasonic beams at high frequency (MHz) (same as that used for ablation) to locally perturb the tissue by generating a low difference frequency (kHz) radiation force. Recording of the tissue response at several locations yields an image. The amplitude of the tissue response depends on the mechanical and acoustic tissue properties, namely its stiffness and absorption. Those two properties were initially hypothesized to have opposite effects in the response amplitude, i.e., the amplitude should increase with absorption and decrease with stiffness. To check this hypothesis as well as the degree to which those properties influence the response, finite-element simulations of a uniform lesion formed in a homogeneous medium were used. The results show that the hypothesis holds at lower frequencies. At resonance and higher frequencies, those two properties have a synergistic effect on the tissue response to the applied radiation force.