Holmium: YAG lithotripsy varies with power settings.

Abstract

The holmium:YAG laser fragments stones by photothermal mechanism. Increased pulse energy (PE) produces larger ablation craters, implying faster lithotripsy. However, increased PE increases retropulsion, implying slower lithotripsy. Optimal power settings were studied. Uniform stone phantoms were ablated in water (500 J total energy). Six power settings were tested: ranging from 0.2 to 2.0 at 10–40 Hz. Two conditions were tested: no stabilization vs stabilization devices placed behind the stone. Total fragmentation (TF) and fragment sizes were quantified. In the no stabilization cohorts, retropulsion was measured. Pressure transients were measured by needle hydrophone. Stone crater volumes were quantified by optical computed tomography. With or without stabilization, TF increased as PE increased, p<0.0001; and fragment size increased as PE increased, p<0.05. Without stabilization, retropulsion increased as PE increased, p<0.0001. TF was greater with vs without stabilization, p<0.01. Pressure transients were <30 bars even at 2.0 J. Crater volumes increased as PE increased, p<0.01 but remained symmetric. Increased PE produces more lithotripsy but also larger fragments. Even at high PE (2.0 J) Ho:YAG lithotripsy is photothermal. Low PE produces small fragments but less lithotripsy. Modest PE (0.2–0.5 J) at high‐repetition rate produces more fragmentation, small fragments, and less retropulsion. [Work supported by Percsys and Boston Scientific.]