Login to Access Video or Poster Abstract: MP62-20
Sources of Funding: Work support by NIH NIDDK grants DK043881 and the National Space Biomedical Research Institute through NASA NCC 9-58.

Introduction

Ultrasonic propulsion (UP) has been successfully demonstrated in a human clinical trial to reposition stones and facilitate spontaneous passage of fragments. Given the prevalence of kidney stones, and the cost related to symptomatic relief of a patient in acute renal colic, a non-invasive ultrasound treatment for immediate pain relief would be of great benefit. Repositioning an obstructing stone and alleviating the acute pain would allow for temporization and a delayed elective vist. The purpose of this study was to use a phantom model to evaluate the effect of stone size and composition on the potential limits of UP to expel stones and fragments using a phantom model.

Methods

The phantom consisted of a 12 mm x 30 mm cylindrical pipette bulb embedded in a tissue mimicking material at 10 cm depth, simulating the uretero-pelvic junction (UPJ) or a calyx within the kidney. Four different stone compositions were tested. Three stones of each type with varying size and weight were treated at the maximum probe intensity and push duration from 0.5 s to 5 s. Stone composition (average weight) included Ammonium acid urate (0.16 g), Struvite (0.62 g), Calcium Phosphate (0.28 g), and Calcium Monohydrate (0.26 g). The aggregate maximal size of the three stones was 8-12 mm. The average number of times a stone was expelled over 10 attempts was assessed for each stone type and over the range of stone sizes. If the stone became trapped within the calyx, two additional push attempts were performed.

Results

The only stones expelled less than 100% of the time were the heaviest stone (Struvite, 0.68 g) that was never lifted high enough for expulsion with a single 0.5 s pulse and the largest stone (CAP, 12 mm x 7 mm), which occasionally became stuck at the 12 mm orifice of the pipette. Multiple pushes did not result in further expulsion of the stuck stone.

Conclusions

This phantom study showed UP of large stones was rather insensitive to stone size or composition. Exceptions occurred with the heaviest and largest stones. Struvite required push durations longer than 0.5 s to move the stone out of the phantom. Also, a stone presenting with a wider aspect than the width of the calyx could not be forced through the smaller opening. A limitation of the study is the force was always optimally aligned with the pipette opening, which may be challenging for stones in the UPJ.

Funding

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