Prediction of overheating close to bone interfaces generated by high intensity ultrasound transducers

Abstract

One of the driving forces for research in medical sciences is to develop more effective and less intrusive treatments. High Intensity Ultrasound (HIU) is a technique that uses the acoustic field produced by a transducer to induce thermal effects in soft tissue for therapeutic purposes like tissue ablation for cancer treatment, localized drug delivery, sonoporation, among others. The bioeffects induced in soft tissue by HIU, particularly close to solid (bone) interfaces, are not yet fully understood. The objective of this thesis work is to gain further understanding of the effects that the waves reflected by bone have on the treatment outcome. This study presents the experimental validation of a simple and efficient method to calculate the acoustic field generated by a high intensity ultra- sound (HIU) transducer that is used in the vicinity of a solid interface. The model takes into account the interaction between the forward and the re- flected wave generated at the boundary between a fluid and a solid. It uses a modified Rayleigh-Sommerfeld integral to calculate the particle displacement over a reflecting surface and uses the particle displacement at the boundary as a new acoustic source to obtain the reflected particle displacement. The thermal effect of the acoustic field is finally calculated using the bio heat transfer equation (BHTE) accounting for both the forward and the reflected waves.