Presentation Authors: Russell Terry, Brenton Winship, Kohldon Boydston*, Evan Carlos, Glenn Preminger, Michael Lipkin, Durham, NC
Introduction: Non-contact or "popcorn" lithotripsy is characterized by continuous laser discharge within a collection of stone fragments resulting in agitation of the stones and surrounding fluid, promoting further lithotripsy and a significant reduction in stone burden. Previous work has established improved results when performed in a calyx versus the renal pelvis and with moderate pulse energy and high frequency. Our aim was to assess the effect of pulse length and pulse type (Moses) on stone ablation in an in vitro popcorn model.
Methods: All tests were conducted using a Lumenis Pulse 120H Holmium:YAG laser with 200 µm Moses fibers. "Hard" (15:3) and "soft" (15:6) BegoStone phantoms mimicking calcium oxalate monohydrate and uric acid stones respectively, were pre-fragmented to 2-4mm size to mimic typical popcorn conditions. 0.5g of fragments were placed into 5mL test tubes and the laser fiber positioned just above the stones. The laser was fired for 2 min with continuous irrigation at 0.5J/70Hz, 0.5J/40Hz, and 1J/20Hz at short pulse, long pulse, Moses-contact, and Moses-distance settings. After drying, the mass of stone reduced to sub-2mm fragments was assessed and analyzed using one-way Tukey's HSD ANOVA and t-tests.
Results: On hard stones, 0.5J/70Hz created significantly more stone ablation than 0.5J/40Hz and 1J/20Hz regardless of pulse type (p=0.006). No difference in mean ablation was seen between 0.5J/40Hz and 1J/20Hz regardless of pulse or stone type. At 0.5J/70Hz, short pulse was significantly more ablative than long pulse and Moses-contact (p=0.03, 0.005). Moses-distance also was significantly more ablative than Moses-contact under these conditions (p=0.03). At all tested parameters, short pulse and Moses-distance were not significantly different. On soft stones, there was no statistically significant difference in ablation between pulse types at any given energy setting. However, at 0.5J/70Hz and 0.5J/40Hz, short pulse and Moses-distance were more ablative than other pulse types. (Figure)
Conclusions: The efficiency of high-power, non-contact "popcorn" lithotripsy of hard stones is impacted by pulse length and type. Short pulse and Moses-distance provide the most ablative popcorn lithotripsy when optimal pulse energy and frequency settings are used. The significance of pulse type is lost at lower power and on softer stones.