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Real-time optical feedback control of laser lithotripsy

Laser lithotripsy is now an accepted modality for the intracorporeal fragmentation of urinary tract and, to a lesser extent, biliary tract calculi. However, under conditions where constant direct vision is not possible or compromised, the risk of inadvertent laser damage to healthy soft tissue cannot be discounted. This is especially true at the higher laser pulse energies required to fragment the more recalcitrant stones. A series of in vitro and in vivo investigations are described which demonstrate a method and apparatus for the automatic feedback control of laser lithotriptors. In preliminary experiments, the control device, incorporated into a commercial flashlamp-pumped dye laser, is shown to significantly improve the margin of safety against laser tissue damage while still allowing effective stone fragmentation. The practical implications of our findings for the clinical possibility of `blind' laser lithotripsy are discussed.