Free electron laser ablation of urinary calculi: an experimental study

Abstract

Infrared laser ablation of urinary calculi was investigated as a function of wavelength to determine the relation of ablation threshold fluences, ablation depths, and optical absorption. A simple photothermal ablation model was employed to examine this relationship. Human urinary calculi composed of 95% uric acid, 95% cystine, 95% calcium oxalate monohydrate (COM), and 90% magnesium ammonium phosphate hexahydrate (MAPH) were used. Various wavelengths between 2.1 and 6.5 m were selected to perform threshold fluence and ablation depth measurements. The laser source for this study was the tunable pulsed infrared free electron laser (FEL) at Vanderbilt University. Experimental results indicated a correlation of threshold fluence and ablation depth to the optical absorption properties of the calculi. When calculus optical absorption increased, the threshold fluences decreased. Although the ablation depths increased with calculus optical absorption, results indicated that in certain calculi the ablation depth was affected by optical attenuation through the ablation plume. These observations were in agreement with the photothermal ablation model, but fractures in striated calculi at higher optical absorptions indicated the contribution of a photomechanical mechanism.

Pulsed Thulium:YAG laser – What is the lithotripsy ablation efficiency for stone dust from human urinary stones? Results from an in vitro PEARLS study

“…Of final note, COM is generally accepted as the “harder” stone to ablate compared to UA [ 9 , 32 , 46 , 47 ]. Astonishingly no significant differences in ablation efficiency were found between these two stone types in the present study.…”

Polymer–Mineral Composites Mimic Human Kidney Stones in Laser Lithotripsy Experiments

“…The most concerning difference between the BegoStone and human stones is that gypsum cement has an infrared absorption spectrum drastically different than human stones in the frequency range exploited for laser lithotripsy. The correlation between the absorption coefficient of a stone material and its fragmentation behavior during lithotripsy is well-documented in the literature. ,− The ideal artificial stone would have identical absorption characteristics as real human stones, thus not only replicating the mechanical properties of human calculi but also the optical properties as well. This is particularly critical because as new lasers are introduced in urology, a reliable stone model is required to optimize laser parameters at a given frequency.…”

“…Our design strategy for new artificial kidney stones is inspired by the photothermal model for lithotripsy presented by Teichman and co-workers which has demonstrated a correlation between fragmentation damage from holmium:YAG lithotripsy and the absorption coefficient of human stones at the wavelength emitted by the holmium laser: 2.12 μm. ,, This model posits that energy transfer from the laser to stone is mediated by photothermal absorption at 2.12 μm, which leads to a temperature increase and decomposition of kidney stones. Thus, the fundamental parameters governing the response of a material to the holmium:YAG laser are its absorption coefficient at 2.12 μm and its threshold radiance, or the power needed to cause chemical decomposition and ablation at the surface of a stone .…”

Femtosecond laser lithotripsy: feasibility and ablation mechanism

“…The pulsed dye laser disintegrates stones through a photomechanical mechanism based on its short pulse duration ͑typically, 1 or 2 s͒. 3,4 In this approach, shock waves are generated as a result of cavitation bubble expansion and collapse, disintegrating stones as they transverse calculi surfaces. 5,6 This method tends to create large-sized debris that may not pass spontaneously through the ureter.…”