Design, Fabrication and Characterization of Ultrasound Transducers for Fragmenting Large Renal Calculi

Thesis (Master's)--University of Washington, 2018One in 11 people is affected by renal calculi (kidney stones) at some point in their life. There are different stone management techniques, but all have associated injuries to kidney or ureter and complications. Burst wave lithotripsy (BWL), developed recently by the Center for Industrial and Medical Ultrasound, has shown promising results for fragmenting stone non-invasively. BWL targets a stone with a series of pulses of small pressure amplitude at regular intervals of time to break the stone while minimizing tissue damage. BWL is still under development and its parameters need to be optimized. One of the challenges of BWL is to develop a transducer that can fragment stones larger than 6 mm. The objective of this work was to develop a transducer that fragmented stones up to 12 mm. This was achieved by using piezoceramic materials that produced sufficient power for the fragmentation of large stones. Acoustic beam patterns were optimized using an iterative angular spectrum approach and rapid prototyped acoustic lenses. Finally, a BWL transducer was designed, fabricated and characterized to confirm the required outputs. The new transducer was demonstrated to fragment 11 mm stones 2.8 times more effectively than existing BWL transducers