Laser lithotripsy: the impact of beam profile and wavelength on stone ablation

Thulium fiber lasers (TFL) with a peak power of 500W were introduced a few years ago for clinical use in laser lithotripsy of urinary stones. To compare the TFL with the current gold standard, the Ho:YAG laser, single pulse experiments were performed at 1.5J from different working distances using a 365μm fiber. For evaluation of the fragmentation properties of both laser systems, cuttlefish bone samples and glued BegoStone cylinders were ablated at 1.5J using different pulse durations. It was found that the TFL produced up to two times higher stone ablation compared to the Ho:YAG laser but showed significantly poorer results in fragmentation which might be explained by its lower peak power. Furthermore, the increase in the ablation efficiency of laser lithotripsy by adjusting the beam profile was investigated in this study. A series of measurements with annular and circular beam profiles of the same beam diameter was performed with the TFL. At a pulse energy of 1J the annular beam profile has removed 90% more stone volume with a single pulse.