An in vitro evaluation of laser settings and location in the efficiency of the popcorn effect.

Abstract

To examine different locations and laser settings' effects on the efficiency of the "popcorn" method of laser lithotripsy, which consists of placing the laser in a group of small stones and firing continuously to break them into smaller particles. Pre-fragmented BegoStones were created between 2 and 4mm to mimic typical popcorning conditions. A 0.5g collection of fragments was placed into 3D-printed models (a spherical calyx and ellipsoid pelvis model) and a 200-µm laser fiber was positioned above the stones. The laser was fired for 2min with irrigation, with 5 trials at each setting: 0.2J/50Hz, 0.5J/20Hz, 0.5J/40Hz, 1J/20Hz, 0.2J/80Hz, 0.5J/80Hz. After drying, fragmentation efficiency was determined by calculating the mass of stones reduced to sub-2mm particles. Statistical analysis was performed with ANOVA and Student's t test. The trials within the calyx model were significantly more efficient compared to the pelvis (0.19 vs 0.15g, p = 0.01). When comparing laser settings, there was a difference between groups by one-way ANOVA [F(5,54) = 8.503, p = 5.47 × 10-6]. Post hoc tests showed a power setting of 0.5J/80Hz was significantly more efficient than low-power settings 0.2J/50Hz and 0.5J/20Hz (p < 0.05). Additionally, 0.2J/50Hz was significantly less efficient than 0.5J/40Hz, 1J/20Hz, and 0.2J/80Hz. Popcorning is most efficient in smaller spaces; we recommend displacement of stones into a calyx before popcorning. No difference was seen between high-power settings, although 0.5J/40Hz and 0.5J/80Hz performed best, suggesting that moderate energy popcorning methods with at least 0.5J per pulse are most efficient.