Berkeley Fluids Seminar
University of California, Berkeley
Bring your lunch and enjoy learning about fluids!
February 3, 2014
Spencer Frank (Mechanical Engineering, UC Berkeley)
Bubble Proliferation Depends on Daughter-Bubble Dissolution Time in Shockwave Lithotripsy
Shockwave Lithotripsy is the most common medical procedure for treating kidney stone disease, an ailment that now affects 1 in 11 persons in the United States. Unfortunately, advances in shockwave treatment have not kept up with the proliferation of the disease, and, paradoxically, newer lithotripters have actually been shown to be less effective than the original lithotripter, the Dornier HM3, which was developed in the 1980s. One of the main mechanisms that destroys kidney stones during lithotripsy is the violent collapse of cavitation bubbles produced by the tensile portion of the shockwave. One hypothesis for the decreased treatment efficiency is that, in the newer lithotripters, the tensile portion of the shockwave is attenuated due to bubble proliferation in the pre-focal beampath. If the tensile wave is highly attenuated when it reaches the stone, cavitation will be reduced in the region where it causes the most stone damage. Utilizing high-speed imaging of the bubble cloud and measurements of the pressure waveform via a fiber optic hydrophone, we systematically test 12 combinations of operating conditions (varying gas concentration in the coupling medium and pulse repetition frequency) and identify those that lead to bubble proliferation. Additionally, a model of bubble dissolution is developed, which estimates the number of daughter bubbles formed by the fragmentation of a single bubble upon collapse. This estimate, which agrees with prior observation, allows the model to successfully capture the threshold where bubbles begin to proliferate. These findings provide a guideline for the combinations of pulse repetition frequency and gas concentration that lead to efficient tensile wave transmission resulting in more effective treatment.