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Plasma formation in holmium:YAG laser lithotripsy
Yuri A Pishchalnikov1, William M Behnke-Parks1, Marshall L Stoller2
1Applaud Medical Inc., San Francisco, California, USA.
Lasers in Surgery and Medicine
|March 30, 2023
Summary
Flashes of light during holmium:YAG laser lithotripsy are caused by plasma formation, not the laser itself. This plasma generation is a key factor in breaking urinary stones and can cause damage to surrounding materials.
Area of Science:
- Biomedical Engineering
- Laser Physics
- Urology
Background:
- Holmium:YAG (Ho:YAG) laser lithotripsy is a common procedure for urinary stone removal.
- Urologists observe visible light flashes during Ho:YAG laser lithotripsy, despite the laser's infrared wavelength.
Purpose of the Study:
- To investigate the origin and characteristics of visible light flashes observed during Ho:YAG laser lithotripsy.
- To understand the physical mechanisms underlying these light emissions and their effects.
Main Methods:
- Ultrahigh-speed video-microscopy and photodetectors were used to analyze Ho:YAG laser pulses.
- Experiments were conducted on urinary stones and hydroxyapatite-coated glass slides in air and water.
- Acoustic transients were measured using a hydrophone.
Main Results:
- Visible light flashes, or sparks, with submicrosecond risetime were observed, originating from intensity spikes in the laser pulse.
- These sparks indicate plasma formation and optical breakdown, enhancing laser absorption.
- Sparks generated shock waves and caused cavitation, leading to damage in 63% of tested glass slides.
Conclusions:
- Plasma formation, previously unappreciated, is an additional physical mechanism of action for free-running long-pulse Ho:YAG lasers.
- Understanding this phenomenon is crucial for optimizing laser lithotripsy procedures and minimizing unintended tissue damage.
