Design and Development of Single Element Focused Ultrasound Transducers

Histotripsy is a non-invasive, non-thermal, and non-ionizing therapy that utilizes converging high-pressure ultrasound waves at a focal point to produce cavitation and induce mechanical tissue destruction. Currently, rapid prototyped histotripsy transducers consist of multiple elements and are made using 3D printing methods. Multi-element transducers introduce size constraints and 3D printing has limitations in material choice, cost, and time for larger scale manufacturing. This thesis investigates the development of rapid prototyped single element histotripsy transducers and the use of injection molding for transducer fabrication, utilizing an in-house metal CNC mill for mold manufacturing and a desktop injection molding machine. Nylon 101 and 30% glass-filled nylon were chosen as the plastics to inject as these were found to have the most similar acoustic properties to WaterShed, an ABS-like plastic currently used. Six single-element transducers were constructed with a 2 MHz curved Pz26 piezoceramic disc: two with SLA 3D printed housing, two with SLS 3D printed housing, and two with injection molded housing. Electrical impedance, beam dimensions, focal pressure output, and cavitation were characterized for each element. The results show that rapid prototyped single element transducers can generate enough pressure to perform histotripsy. This marks the development of the first rapid prototyped single element histotripsy transducer and further confirms that injection molding can produce transducers comparable, if not identical or potentially superior, to 3D printed counterparts. Future work aims to further characterize these transducers, explore more material options, and apply injection molding to various transducer designs while optimizing both CNC and injection molding parameters.