Customization of acoustic output in lithotripsy using a piezoelectric transducer array

Abstract

A piezoelectric array was employed to examine the role of waveform shaping on stone fragmentation in lithotripsy. The array consisted of 170 elements placed on the inner surface of a 15-cm-radius spherical cap. Each element was driven independently using 170 individual pulsers—each capable of generating 1.2 kV. The acoustic field was characterized using a fiber optic probe hydrophone with a bandwidth of 30 MHz and a spatial resolution of 100 μm. When all elements were driven simultaneously, the focal waveform was a shock wave with peak pressures p+=65±3 MPa and p−=−16±2 MPa and the focal region was cigar shaped: 13 mm long and 2 mm wide. The firing of group of elements was adjusted so that each groups focused to different locations in the geometric focal plane. This method allowed the width of the focal region to be broadened albeit with decrease in peak pressure: for a 3-mm-wide region p+=32 MPa and for a 4-mm focal region p+=25 MPa. Waveform shaping was used to enhance or suppress cavitation effects where cavitation activity was observed using a dual passive cavitation detector consisting of two 1-MHz focused transducers. Stone fragmentation was assessed by treating artificial stones with fixed number of shock waves. [Work supported by NIH.]