Plasma Shield Lasertripsy: In Vitro Studies

Abstract

A technique for safer and more effective pulsed laser lithotripsy of urinary and biliary calculi was investigated in vitro. The technique involved enclosing the distal end of the laser delivery fiber in a plasma shield, which is a specially designed metal cap that serves to transfer the laser-induced mechanical impulse to the calculus while shielding surrounding tissue from direct laser exposure and thermal radiation. The metal cap also offers the advantage of effectively blunting the sharp fiber tip and improving visualization of the fiber tip during fluoroscopy.

Plasma shield lithotripsy using a 200-micron quartz laser fiber inserted into a section of a modified.034-inch diameter stainless steel guide wire was tested in vitro on a variety of calculi. Results were compared to those obtained using a 200-micron quartz laser fiber applied directly to a variety of calculi. Calculi tested included cystine, struvite, and calcium oxalate dihydrate (COD) urinary stones and pigmented cholesterol gallstones. The laser source was a flashlamp-pumped dye laser, which produced pulses of 1.2 microsecond duration. The laser operated at a wave length of 504 nm and pulse repetition frequency of 5 Hz.

The results show that plasma shield lasertripsy is as effective as direct lasertripsy for fragmenting gallstones, struvite and COD calculi. Plasma shield lasertripsy may be safer than direct lasertripsy, and it can fragment cystine calculi, which cannot be fragmented by direct application of the pulsed dye laser.