Stone retropulsion during holmium:YAG lithotripsy

Area of Science:

• Urology
• Biomedical Engineering
• Laser Physics

Background:

• Holmium:YAG lithotripsy is a common procedure for kidney stone removal.
• Understanding and controlling stone retropulsion is crucial for procedural efficiency and safety.
• The physics governing retropulsion during lithotripsy are not fully elucidated.

Purpose of the Study:

• To model retropulsion during holmium:YAG lithotripsy based on the principle of conservation of momentum.
• To test the hypothesis that ejected stone debris causes retropulsion.
• To investigate the influence of laser parameters and fiber optics on retropulsion.

Main Methods:

• Modeled retropulsion using conservation of momentum principles.
• Irradiated calculous phantoms with holmium:YAG laser in air and water.
• Varied optical fiber diameter and pulse energy, monitoring phantom motion with high-speed video.
• Characterized laser-induced crater volume and geometry using optical coherence tomography.
• Analyzed ejected plume direction using laser-burned paper.

Main Results:

• Retropulsion was significantly greater in air than in water.
• Retropulsion increased with increasing fiber diameter and pulse energy (p <0.001).
• Crater volume increased with pulse energy and generally with fiber diameter.
• Larger fibers produced wider, shallower craters; smaller fibers produced narrower, deeper craters.
• Ejected plume direction was consistently normal to the irradiated surface.

Conclusions:

• Retropulsion during holmium:YAG lithotripsy is directly correlated with pulse energy and optical fiber diameter.
• Vector analysis of plume dynamics and crater geometry explains increased retropulsion with larger fibers.
• Performing holmium:YAG lithotripsy with smaller optical fibers is recommended to minimize stone retropulsion.