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Contact Holmium-laser lithotripsy: Effect of dusting and fragmentation settings on stone models using an automated 3-D gantry system


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Contact Holmium-laser Lithotripsy: Effect Of Dusting And Fragmentation Settings On Stone Models Using An Automated 3-D Gantry System



•Holmium laser systems are now able to offer fragmentation and dusting (low-pulse energy and high-frequency) settings for lithotripsy.
•Most in vitro studies in this field have explored fragmentation using rudimentary motion systems.
•In this study we assessed the effect of different laser settings on fragmentation utilizing an automated 3-D gantry system for moving the laser fiber using two widely available stone models.
•We tested two stone models: BegoStone (15:3 powder to water ratio) and Ultracal 30 (100:38 powder to water ratio).
•Stones were 30 (l) x 30 (w) x 3 (h) mm in size and 3 stones from each stone model were used for each experiment.
•For holmium laser lithotripsy we used a 60-Watt system (VersaPulse, PowerSuite, Lumenis, CA) and 200 µm fiber (Flexiva 200, Boston Scientific, MA).
•The laser fiber was positioned with a fiber chuck that was connected to a customized 3-D positioner (Velmex, NY). For each experiment, the positioner was programed using Matlab (MathWorks, MA) to advance the at a speed of 1 mm/s to make 10 connected lines 20 mm long with 2 mm spaces in between (Figure 1).
•Laser settings assessed were either 8 or 16 Watt: 0.2 J X 40 Hz (8 W), 0.4 J X 20 Hz (8 W), 1.0 J X 8 Hz (8 W), 0.4 J X 40 Hz (16 W), 0.8 J X 20 Hz (16 W), and 1.6 J X 10 Hz (16 W).
•Stone fragmentation = initial stone weight – post experiment weight.
•Micro-sieves (1 and 0.5 mm) were used to determine sub-millimeter stone fragmentation (dusting) effect.
•Stone fragmentation at different laser settings for the two stone models is shown in Figure 2.
•For BegoStone stones, fragmentation increased when the pulse energy was increased. In contrast, Ultracal stones did not show a similar trend.
•Regardless of the laser setting, none of the stone models produced fragments >0.5 mm in size. 
•BegoStone stone model was more consistent than Ultracal stone model; however, it is unknown if their response to laser lithotripsy mimic human stone response for dusting settings and fragmentation.

Our work suggests the need for validating the currently used stone models to ensure they replicate clinical findings in the era of high frequency laser lithotripsy.  

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