Influence of optical absorption on urinary calculus threshold fluence and ablation efficiency during infrared laser ablation

Abstract

ABSTRACT The objectives of this study were to determine if the optical absorption properties of urinary calculi affect thethreshold fluence for ablation or fragmentation and the ablation efficiency due to laser irradiation. The Vanderbiltfree electron laser (FEL) was tuned to selected wavelengths based on the absorption spectrum of various types ofurinary calculi. The threshold fluences for ablation of the calculi were measured at different wavelengths. Apreliminary study of the ablation efficiency (ablation depth per unit incidence fluence) was performed. The resultswere found to be in agreement with a thermal ablation model for which the threshold fluences were proportional to 1/J.ta. The ablation efficiencies were higher in regions of the infrared spectra in which absorption was higher. For afixed laser irradiation, the lower threshold fluences within regions of high optical absorption allowed more energy toenhance calculus ablation. This study provided insight into determining the optimum wavelengths for ablation andlaser lithotripsy.Keywords: ablation efficiency, absorption coefficient, fragmentation efficiency, free electron laser, infrared, kidneystone, optimum wavelength, threshold radiant exposure, tissue ablation.