Effect of Controlled Sound Pressure Field on Fragmentation in Piezoelectric Extracorporeal Shock Wave Lithotripsy

A method for changing a sound pressure field by electronic driving control of individual piezoceramic elements is studied so that extracorporeal shock wave lithotripsy may become a more effective and safer therapeutic method. First, we examine this method with respect to the field of a shock wave. At 1 kV driving voltage, the focal zone can be changed from 2.2 mm×7.1 mm to 2.8 mm×34.0 mm, and the peak pressure can be decreased to 64% of the original value. The change of fragmentation ability in this method is shown by measuring the number of shots required to break a model stone. The fragmentation is the most intense at a point 10 mm in front of the focal point, and the fragmentation ability remains as effective even if peak pressure is decreased. This method can decrease the peak pressure while maintaining the fragmentation effect.