A Low-Cost Miniature Histotripsy Transducer for Precision Tissue Ablation

A miniature, 10 mm aperture histotripsy transducer with an f-number of 0.7 was fabricated using an elliptically shaped aluminum lens, which was epoxy-bonded to an air-backed 5.0 MHz, PTZ-5A, 1-3 dice-and-fill piezoelectric composite, and the lens coupled to water using a quarter-wavelength matching layer of Parylene-C. A Krimholtz-Leedom-Matthaei model of the device and curved lens was developed. The epoxy layer resulted in an increased power output at 6.8 MHz compared to the 5 MHz composite design. Cavitation was observed in water by driving the composite with a 173 V single-cycle, unipolar 6.8 MHz pulse at a pulse repetition frequency of 50 Hz, and a bubble cloud 264 long by 124 wide was measured. A coregistered imaging and ablation device was also fabricated and characterized. The coregistered device was modified to include a mm square hole through the center, allowing access for a high-frequency imaging array, and both imaging and ablation are demonstrated in cerebral tissue with this device. Radial -3 dB beam widths were measured as 0.145 and 0.116 mm, and axial -3 dB depths of field were 0.698 and 0.752 mm for the noncoregistered and coregistered transducers, respectively. Total material cost for the transducer and pulser board is below $200 USD.