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 /spl mu/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.
Highlights
I NTERVENTIONAL treatments of urinary calculi have improved drastically over the past two decades
The measured threshold fluences for ablation in the infrared spectrum are strongly influenced by the optical absorption of the calculi
We have demonstrated in this study that the ablation process is highly dependent upon optical absorption
Summary
I NTERVENTIONAL treatments of urinary calculi have improved drastically over the past two decades. By the early 1990s, four major lithotripsy modalities have been used clinically to remove urinary or renal calculi. They include electrohydraulic lithotripsy (EHL), ultrasonic lithotripsy, extracorporeal shockwave lithotripsy (ESWL) and laser lithotripsy [1]. Each of these modalities has its limitations. Laser lithotripsy allows the use of small-diameter catheters, which provide access to both ureteral and renal calculi. This technique has been shown to reliably remove calculi with minimal damage to healthy tissue without the use of ureteroscopy
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