High-speed photographic evaluation of holmium laser

Little information has been published regarding the relative contributions and exact mechanisms involved in stone fragmentation during holmium laser lithotripsy. High-speed photography has been used to evaluate other intracorporeal lithotripsy devices, and we chose this method to evaluate the holmium laser. High-speed photographic evaluation of cavitation bubbles produced by the four fiber sizes (200, 365, 550, and 1000 microm) showed a moderate degree of correlation (n = 0.71 for 1 J pulses, r = 0.80 for 4 J pulses) between maximal bubble size and fiber diameter. Eliminating the data from the eroded 550 microm fiber strengthened the correlation to r = 0.94 for 1 J pulses and r = 0.99 for 4 J pulses. The importance of keeping fiber tips in good working condition was thereby demonstrated. Evidence of a thermal effect of the laser on stone and chalk was also obtained. In a parallel study, no correlation (r = -0.08) was found between fiber diameter and stone fragmentation efficiency using chalk as an in vitro stone model.