Bifocal reflector for electrohydraulic lithotripters

OBJECTIVE: To describe the design and construction of a bifocal reflector that could be used in electrohydraulic extracorporeal shockwave lithotripters in order to increase their efficiency. METHODS: The new reflector is obtained by joining two sectors of two rotationally symmetric ellipsoidal reflectors having different distances between their foci, which results in a bifocal composite reflector with the F1 foci in coincidence and the two F2 foci separated by a certain distance. As in conventional reflectors, shockwaves are generated by the electrical breakdown of water between two electrodes, located at the focus (F1) closest to the reflector. A prototype was constructed and tested in an experimental shockwave generator of our own make, using two different types of kidney-stone models, one to test the stone fragmentation abilities, and the other to test the stone pitting abilities. Fragmentation data for the new reflector were compared with those of a conventional ellipsoidal reflector tested on the same device. RESULTS: The new design appeared to be more efficient in breaking up both types of kidney-stone models than the conventional reflector. Pressure measurements were obtained with both reflectors using needle hydrophones. The physical background of shockwave reflection on both reflectors is also explained. CONCLUSION: With this new reflector, it could be possible, in principle, to reduce the treatment time of extracorporeal shockwave lithotripsy.