Dual mode piezoelectric lithotripter for efficient breakup of urinary stones

Abstract

The coalescence and dispersion of cavitation bubbles through Bjerknes forces created by supplemental low amplitude acoustic fields has been shown to greatly improve the efficiency of shockwave lithotripsy for breaking urinary stones. Unfortunately, the large size of extracorporeal lithotripters typically leaves little acoustic window for additional transducers to create these fields. In this study, we explored the feasibility of using a piezoelectric lithotripter transducer in a dual mode generating both shockwaves for stone comminution and low amplitude tone bursts for bubble coalescence and dispersion. A piezoelectric lithotripter head and driver unit (piezolith 3000) was provided by the manufacturer (Richard Wolf GmbH). A custom class-D driver circuit was constructed from very high voltage blocking IGBTs and wired in parallel with the manufacturer’s excitation circuit for shockwave generation. Acoustic output was measured with a fiber optic probe hydrophone at the focus in a tank of degassed water. The driver produced acceptable 200 kHz tone bursts of 5–100 cycles up to at least 1 MPa amplitude. Lithotripter power settings 1–3 could be safely used with the combined driver and were sufficient to break model begostones in vitro. Future studies will compare efficiency of stone comminution using the dual mode system.