A burst wave lithotripsy system for urinary stones in pet cats

Upper urinary tract stones are becoming more prevalent in cats. Surgery to address obstructing stones has poor outcomes and such stones can rarely be treated with medical therapy. Burst wave lithotripsy (BWL) is a non-invasive, ultrasound-guided, handheld focused ultrasound technology to disintegrate urinary stones, which is now in human clinical trials. In this project, we created a scaled version of the system for use on pet cats, adjusting geometric parameters and frequency of the transducer to account for differences in anatomic scale and stone size. A 650-kHz prototype transducer was fabricated, calibrated, and tested on 25 natural feline stones 2–5 mm applying 20-cycle pulses at 10 Hz pulse repetition rate with three different focal pressure amplitudes ≤8.9 MPa in an in vitro tissue phantom. The fragments were sieved in 10-min intervals to assess breakage. The results demonstrated that between 73%–96% of the stone mass was reduced to fragments i<1 mm in a 30-min exposure, with only 2/25 stones showing no visible fragmentation. These data suggest BWL can fragment feline ureteral stones and that a high-frequency system can produce small fragments more likely to pass through the small ureter of a cat. [Work supported by NIDDK P01 DK043881.]