Login to Access Video or Poster Abstract: MP62-06
Sources of Funding: Work support by NIH NIDDK grants DK043881 and the National Space Biomedical Research Institute through NASA NCC 9-58.

Introduction

In our first-in-human trial with ultrasonic propulsion (UP), we moved stones in 14 of 15 subjects and 4 post-lithotripsy subjects passed an aggregate of over 30 stone fragments. Our experience suggested probe heating would limit the duration of the push pulse and the rate at which treatment could be delivered with the clinical C5-2 probe. We have developed a new UP probe (SC-50) that provides a more uniform beam design with greater focal extent in depth and reduced probe heating.

Methods

The calyx phantom consisted of a pipette (12 mm x 30 mm) embedded in a block of tissue mimicking material at two skin-to-stone depths (4.2 cm and 9.5 cm). Three separate targets were placed into the pipette: a single 7 mm x 4 mm calcium oxalate stone, ten 1-2 mm calcium oxalate fragments, and ten 2-3 mm calcium oxalate fragments. The original C5-2 probe or the new SC-50 probe was positioned below the phantom pushing against gravity. Ten pushes at maximum focal intensity were applied, The C5-2 probe was tested with a push duration of 50 ms, the maximum used in human clinical trial, while the SC-50 probe was tested with push durations of 50 ms and 3000 ms. The capability of the two probes to expel the stone or fragments with each push was summed over the ten push attempts.

Results

Stone expulsion was similar for the C5-2 and the new SC-50 probe with a push duration of 50 ms. No stones or fragments were expelled the full 30 mm distance with the C5-2 probe and only 2-3% of the stone fragments were expelled with the SC-50 probe. Extending the total Push duration to 3000 ms, available only with the SC-50 probe, results in 100% of stones and all fragments expelled independent of depth from 4.5 cm to 9.5 cm and with less temperature rise within the probe.

Conclusions

We have developed a new custom designed probe for ultrasonic propulsion that allows for longer duration pushes and reduced probe heating than the commercial probe used in our first-in-human clinical trial, and thus allows for longer duration pushes, than the first-in-human clinical system. The new probe provides similar focal intensity up to 10 cm depth and is significantly more efficient at clearing single stones and stone fragments of various sizes at a range of skin to stone distances. The longer duration push has been shown safe in preclinical studies . Future work is currently in progess for FDA approval of the new probe.

Funding

Work support by NIH NIDDK grants DK043881 and the National Space Biomedical Research Institute through NASA NCC 9-58.