Experimental utilization of the holmium laser in a model of ureteroscopic lithotripsy : Energy analysis

Medical lasers have rapidly expanded in both indications and utilization. We have developed a simple model for the investigation of various modalities of lithotripsy using readily available silicate stones of uniform mass. The holmium:YAG VersaPulse Select (Coherent, Palo Alto, CA) was used in these experiments to define the relation between fiber diameter and efficacy of stone fragmentation. For each fiber, lithotripsy was performed in an incremental fashion at 0.6, 0.8, and 1.0 J at a frequency of 10, 16, and 20 pulses per second at each energy level. Total kilojoules did not differ between any fibers investigated, supporting the consistency of our methodology. The power density of the holmium laser energy, as expressed as total kJ/area, decreases in proportion to increasing fiber diameter. We expected an increase in fragmentation success as fiber diameter decreased (at equal energy output). However, peak lithotripsy occurred with the 365- and 550-microm fibers, whereas neither the 200- nor the 1000-microm fibers was effective. This model utilizing a silicate stone phantom supports our clinical observation that the 365-microm fiber (and additionally the 550-microm fiber) provides the best method for efficient intracorporeal lithotripsy.