Laser-induced shock wave lithotripsy with a regenerative energy converter

Two main mechanisms govern the field of laser lithotripsy. The first mechanism produces mechanical stress inside the stone by absorbing the laser light at the stone surface. Therefore it depends on the stone's optical properties. The second method uses a Q-switched laser and an energy converter to release mechanical shock waves acting on the stone to cause its fragmentation. This method is called laser-induced shock wave lithotripsy (LISL). The converter must be attached to the light transmitting optical fibre and should not provide an increase of the overall diameter of the probe to fit in a small, flexible endoscope. So we used the irrigation liquid, which must be supplied for endoscopic lithotripsy. Adding of Fe³⁺-ions to the isotonic saline solution (0.02 mmol l⁻¹) lowered the intensity threshold for the energy conversion. With this special irrigation liquid we have a continuously regenerating energy converter. It allows the use of bare fibres with spherically shaped tips, which can be easily changed while the endoscope remains inside the patient's body.