An Acoustic Fluid-structure Simulation of a Theraputic Ultrasound Wire Waveguide Apparatus

The use of high-power low-frequency ultrasound transmitted down small diameter wire waveguides is an emerging technology that may have potential in the treatment of complicated atherosclerotic plaques in cardiovascular surgery. This form of energy delivery results in vibrating the distal-tip of the wire waveguide disrupting material by means of direct contact ablation and also cavitation, pressure waves and acoustic streaming in the surrounding fluid. This work describes a numerical acoustic fluid-structure model of the ultrasound wire waveguide and blood surrounding the distal tip. The structural analysis of the model predicts the natural frequencies of the waveguide and shows the extent to which these are affected by the presence of the distal-tip geometry, the surrounding fluid and the length of wire waveguide. These results are validated against experimental results on a 23.5 kHz waveguide apparatus. The acoustic fluid results show the pressure field developed in the surrounding blood and predicts pressure conditions sufficient to cause cavitation in a region close to the distal-tip. These results compare favourably with experimental measurements reported in the literature. The model will prove a valuable design tool in the further development of this potential minimally invasive technology.