Study of cavitation bubble dynamics during Ho:YAG laser lithotripsy by high-speed camera

Although laser lithotripsy is now the preferred treatment option for urolithiasis, the mechanism of laser pulse induced calculus damage is still not fully understood. This is because the process of laser pulse induced calculus damage involves quite a few physical and chemical processes and their time-scales are very short (down to sub micro second level). For laser lithotripsy, the laser pulse induced impact by energy flow can be summarized as: Photon energy in the laser pulse. photon absorption generated heat in the water liquid and vapor (super heat water or plasma effect). shock wave (Bow shock, acoustic wave). cavitation bubble dynamics (oscillation, and center of bubble movement, super heat water at collapse, sonoluminscence). calculus damage and motion (calculus heat up, spallation/melt of stone, breaking of mechanical/chemical bond, debris ejection, and retropulsion of remaining calculus body). Cavitation bubble dynamics is the center piece of the physical processes that links the whole energy flow chain from laser pulse to calculus damage. In this study, cavitation bubble dynamics was investigated by a high-speed camera and a needle hydrophone. A commercialized, pulsed Ho: YAG laser at 2.1 mu m, StoneLight(TM) 30, with pulse energy from 0.5J up to 3.0 J, and pulse width from 150 mu s up to 800 mu s, was used as laser pulse source. The fiber used in the investigation is SureFlex TM fiber, Model S-LLF365, a 365 um core diameter fiber. A high-speed camera with frame rate up to 1 million fps was used in this study. The results revealed the cavitation bubble dynamics (oscillation and center of bubble movement) by laser pulse at different energy level and pulse width. More detailed investigation on bubble dynamics by different type of laser, the relationship between cavitation bubble dynamics and calculus damage (fragmentation/dusting) will be conducted as a future study.