Free electron laser lithotripsy: threshold radiant exposures

Area of Science:

• Biophysics
• Materials Science
• Urology

Background:

• Urinary calculi (kidney stones) pose a significant health challenge.
• Effective fragmentation of calculi is crucial for successful lithotripsy.
• Understanding the interaction of laser wavelengths with calculi composition is key to optimizing treatment.

Purpose of the Study:

• To establish the threshold radiant exposures for infrared laser ablation of various urinary calculi.
• To investigate the relationship between these thresholds, infrared wavelengths, and optical absorption coefficients.
• To determine the correlation between ablation thresholds and lithotripsy efficiency.

Main Methods:

• Human calculi (uric acid, calcium oxalate monohydrate, cystine, magnesium ammonium phosphate hexahydrate) were irradiated.
• A free electron laser (FEL) was used at six infrared wavelengths (2.12–6.45 µm).
• Threshold radiant exposures were measured as a function of wavelength and calculus type.

Main Results:

• Threshold radiant exposures increased with decreased optical absorption.
• Thresholds exceeded 1.5 J/cm² at low-absorption near-infrared wavelengths.
• Thresholds dropped below 0.5 J/cm² in high-absorption regions for all calculus types.
• Differences in thresholds between high- and low-absorption regions were statistically significant (P < 0.05).

Conclusions:

• Optical absorption coefficients predict lithotripsy efficiency.
• Lower ablation thresholds require less radiant exposure for material breakdown.
• Reduced energy for breakdown leads to increased fragmentation and higher lithotripsy efficiency.