Cavitation Bubble Dynamics For Biomedical Applications: Shockwave and Ultrasound Bubble Interaction Simulation

Abstract

Medical treatments involving the use of shockwaves and ultrasound are gaining popularity. When these strong sound waves are applied, cavitation bubbles are generated in nearby tissues and bodily fluids. This thesis aims to study the complex bubblesb interactions with the tissues and among themselves. Simulations are done using the Boundary Element Method (BEM) which has computational efficiency advantage as compared to other numerical methods. Firstly, the interaction between a shockwave and a bubble is modeled and verified against experimental results. A temporally inverted lithotripter shockwave is tested. This waveform has the potential benefit of minimizing collateral damages to close-by tissues or blood vessels. Next, the non-spherical bubble dynamics near a biomaterial in a medical ultrasound field is investigated. Complex bubble behaviors are observed; for certain cases, the bubble jets towards the biomaterials, and in other conditions it forms high speed jets away from the materials. Also, the model is extended to study a microbubbleb s interaction with high intensity pulsed ultrasound proposed for tissue cutting (histotripsy). In medical applications, multiple bubbles are often involved. To provide better understanding of multiple bubble interaction, an experimental study using high speed photography of spark-generated bubbles is performed. Corresponding numerical simulations are done to compare and highlight the details of the complex fluid dynamics involved. Good agreement between the experimental data and the 3D BEM results are obtained. The thesis concludes with discussions on its scientific contributions, some new development in acoustic bubble applications (for example microbubble contrast agents for cancer treatment), and hazards involved in the use of ultrasound in medical therapy. It ends with a conclusion and some suggestions for future work.