Simulations of Shock Wave and Laser Lithotripsy

Shock Wave Lithotripsy (SWL) is a highly effective treatment for the removal of kidney stones. The generated shock waves break up kidney stones into smaller fragments through a dynamic fatigue process involving the contribution of various stress-waves such as surface and compressive waves, propagating respectively on the surface and through the bulk of the stone, and the cavitation produced in the surrounding liquid medium. When the kidney stone breaks into small fragments, they can be delivered out of the body. Therefore, SWL has become one of the most popular non-intrusive medical treatment for kidney stones.

In this research project, the finite element method is used for the simulation of acoustic and solid media, while the appropriate interactions between the fluid and solid domains are enforced. Acoustic waves are generated in the fluid domain by considering an acoustic source of a certain shape in the governing differential equation. The generated acoustic wave hits the solid, which in turn results in compressive waves propagating through the bulk in addition to tensile surface waves traveling on the solid surface. In the experiments, it is observed that this tensile surface wave results in a circular ring like damage occurring at a certain distance from the acoustical source. To date, our simulations (animation below) are capable of representing this same kind of phenomena.  

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(Left) Acoustic wave propagation in fluid domain and its interaction with solid. (Right) Damage evolution on the surface of the solid due to propagation of surface tensile wave.

Laser lithotripsy (LL) is another popular process by which kidney stones are broken up by laser pulses from the end of an endoscopic probe. In this research project, a computational model is developed to simulate the fragmentation process of solid in three dimension using phase field damage model for dynamic fracture. The model was modified to include heat conduction and thermo-mechanical coupling to model the interaction of laser pulses with kidney stones.