Free electron laser lithotripsy: threshold radiant exposures.

Kin Foong Chan,H Stan Mcguff,Joel M.H Teichman,Ashley J Welch,E Duco Jansen,Bernard Choi,Daniel X Hammer,Hans Pratisto

doi:10.1089/end.2000.14.161

Abstract

To determine the threshold radiant exposures (J/cm2) needed for ablation or fragmentation as a function of infrared wavelengths on various urinary calculi and to determine if there is a relation between these thresholds and lithotripsy efficiencies with respect to optical absorption coefficients. Human calculi composed of uric acid, calcium oxalate monohydrate (COM), cystine, or magnesium ammonium phosphate hexahydrate (MAPH) were used. The calculi were irradiated in air with the free electron laser (FEL) at six wavelengths: 2.12, 2.5, 2.94, 3.13, 5, and 6.45 microm. Threshold radiant exposures increased as optical absorption decreased. At the near-infrared wave-lengths with low optical absorption, the thresholds were >1.5 J/cm2. The thresholds decreased below 0.5 J/cm2 for regions of high absorption for all the calculus types. Thresholds within the high-absorption regions were statistically different from those in the low-absorption regions, with P values much less than 0.05. Optical absorption coefficients or threshold radiant exposures can be used to predict lithotripsy efficiencies. For low ablation thresholds, smaller radiant exposures were required to achieve breakdown temperatures or to exceed the dynamic tensile strength of the material. Therefore, more energy is available for fragmentation, resulting in higher lithotripsy efficiencies.

Highlights

LASERS HAVE BEEN USED EXTENSIVELY for fragmenting urinary1"8 and biliary9"11 calculi
This study demonstrated that the ablation threshold of uri¬ nary calculi is dependent on the optical absorption
The compositions of the biliary calculi are not known. It is not clear if the rela¬ tion between the ablation threshold and absorption coefficient found in this paper extends to the visible region, the studies of Dretler and Long et al indicate that they may

Summary

Introduction

LASERS HAVE BEEN USED EXTENSIVELY for fragmenting urinary1"8 and biliary9"11 calculi. The fragmentation mechanism for the Q-switched Nd:YAG and pulsed-dye lasers is predominantly photomechanical or photoacoustical.[12]. In the former, both optical breakdown of water and bubble collapse generate Shockwaves on the order of 100 bar that fragment the calculus.13"15 In the latter, plasma expansion generates a smaller Shockwave than is produced by the bubble collapse, and this second Shockwave produces calculus fragmentation.[7,14,15]. Calculus fragmentation is highly localized and directional.[21,22]. This condition effectively minimizes or prevents collateral tissue damage. The ablation process yields smaller fragments, allowing easier passage through the urinary tract.[28]

Methods

Results

Conclusion