Presentation Authors: Ali H Aldoukhi*, Kristian M Black, Timothy L Hall, William W Roberts, Khurshid R Ghani, Ann Arbor, MI
Introduction: Dusting technique during laser lithotripsy is the use of low pulse energy (PE) and high frequency to achieve submillimeter fragments. In theory, increasing the frequency can increase fragmentation but it is not understood if there is a threshold at which its effect on lithotripsy is limited. The aim of this in vitro study was to assess the effect of frequency on (1) stone crater volume at a fixed location and (2) fragmentation in relation to when the fiber is moving.
Methods: Two sets of experiments were conducted using a flat BegoStone (15:5) with a laser PE setting of 0.5J (Long Pulse). Energy was delivered from a 120W Ho:YAG laser (Moses P120, Lumenis) by a 230 Î¼m core fiber (Moses 200, Lumenis). The relationship of frequency (Hz; number of pulses/second) on crater volume was assessed with the fiber fixed and fired in contact with the stone for 1, 5, 10, 15, 20, 25, 30, 35, and 40 pulses. Crater volume was measured by 3D laser confocal microscopy. Fragmentation was then assessed at 20.40. and 60 Hz, with the fiber attached to a 3D positioner to make 10 lines (each 20 mm length), to mimic a &[Prime]painting&[Prime] technique. For each setting the fiber was moved at a speed of 1 and 3 mm/s equating to 3.3 and 1.1 minutes of lithotripsy time, respectively. Fragmentation was defined as difference in stone mass before and after each experiment. Five trials were performed for each experiment. Two sample t-test was used to compare cohort means.
Results: When the fiber is kept stationary, crater volume increased with increasing the number of pulses but after 20 pulses there was minimal increase in volume (Figure 1A). However, with the fiber moving, fragmentation was significantly greater at higher frequencies (Figure 1B). For all frequency settings, more fragmentation occurred at 1 mm/s compared to 3 mm/s (Figure 1B; p < 0.0002). Increasing the Hz from 20 to 40, and 20 to 60 Hz at 1 mm/s increased fragmentation by 38% and 53%, respectively.
Conclusions: When the laser fiber is fixed, 20 pulses is the threshold after which increasing the number of pulses leads to minimal gain in ablation. However, when the fiber is moving, increasing the frequency increases fragmentation. Further studies are needed to determine the frequency threshold for efficiency, and we posit this threshold may be reached at 80 to 100 Hz at 1 mm/s.
Source of Funding: Research grant from Boston Scientific.