The impact of the geometry of the lithotriptor aperture on fragmentation effect at extracorporeal shock wave lithotripsy treatment.

The aim of this study was to determine the impact of the aperture size of an electro-hydraulic lithotriptor on the fragmentation effect. We also wanted to investigate whether a potential change in the capacitance of the pulse forming network (PFN), at a certain energy level, might have an impact on fragmentation rate. Two different apertures with a diameter of 23 and 17 cm respectively were compared using two different values of total PFN capacitance: 50 nF and 80 nF. Model stones of similar size and weight were fragmented. The number of shots for complete fragmentation or the grade of fragmentation after a certain number of shots was measured. This study shows that for the shock wave system used, the 23-cm aperture seems to provide more effective fragmentation as function of the number of shots compared with the 17-cm aperture at the same energy level. Furthermore, a minor change in the PFN capacitance between reasonable limits does not affect the fragmentation efficiency. This article also highlights the fact that it is not relevant simply to compare the voltage level given in the shots in extracorporeal shock wave lithotripsy treatment between different lithotriptors.