Vapor Channel Oscillations in Laser Lithotripsy

Area of Science:

• Medical physics
• Laser-tissue interactions
• Endoscopic surgery

Background:

• Laser endoscopic procedures face challenges in energy delivery, especially when direct fiber-target contact is not feasible.
• Vapor bubbles and channels are crucial for transmitting laser energy to targets in such scenarios.
• Understanding vapor channel dynamics is vital for improving ablation efficiency, stone movement, and overall procedure safety.

Purpose of the Study:

• To investigate the characteristics and dynamics of laser-induced vapor channels.
• To determine how vapor channel properties influence laser energy transmission and ablation efficiency.
• To provide insights for optimizing laser lithotripsy procedures.

Main Methods:

• A simplified experimental model using a thulium fiber laser (1940 nm) in a water-filled cuvette.
• Vapor channel generation at varying fiber-target distances (1-5 mm) and laser powers (500-1000 W).
• High-speed video recording (24,260 fps) synchronized with laser power transmission measurements.

Main Results:

• Laser-induced channel transmission exhibited oscillations with periods dependent on fiber-target distance.
• Energy transmission decreased linearly with increasing pulse duration and fiber-target distance.
• Vapor bubble expansion showed a pear shape with periodic irregularities due to internal water droplets.

Conclusions:

• Laser-induced channel oscillations provide quantitative data linking fiber-target distance to energy transmission and ablation efficiency.
• These findings are critical for optimizing the safety and duration of laser lithotripsy procedures.
• The study offers insights that may help reduce stone retropulsion during procedures.