Login to Access Video or Poster Abstract: MP62-07
Sources of Funding: Acknowledge NIH DK043881, DK104854

Introduction

In vitro lithotripsy experiments are often conducted in conditions that do not realistically reflect those in vivo. New lithotripsy devices and modalities for nephrolithiasis such as Burst Wave Lithotripsy (BWL) will require in vitro testing to identify appropriate output parameters. To create a more clinically relevant model, we investigated the effects of fluid gas concentration, temperature, stone holder, and model stone composition on fragmentation.

Methods

We performed experiments in an acrylic tank with 53-gallons of deionized water. A motorized 3-axis positioning arm was used to position the stone holder. A BWL transducer was positioned in the tank with a targeting P4-2 ultrasound probe. Water gas concentration was controlled by recirculating water through an evacuated membrane contactor. Water temperature was controlled by an immersion heater. We compared three different kidney phantoms as stone holders including open wire basket, polyvinyl chloride (PVC) open-ended gel, and a Blue Phantom anatomic kidney phantom. Artificial and human stones from 5-9 mm were compared, including Begostone at 2 different mixture ratios, calcite, calcium oxalate monohydrate (COM), and uric acid (UA) stones. At least 3 stones were treated for each condition with BWL for 30 min, and assessed every 10 min as percentage of stone treated to fragments < 2mm.

Results

Begostone(2:1 powder:water ratio) treated in water at room temperature (20°C) vs. body temperature (37°C) showed 75±13% vs. 62±6% breakage at completion, respectively. The same stone type showed a water-gas concentration dependent response with 23±4%, 55±8%, and 82±16% breakage at 60, 30, and 15% O₂ respectively. Kidney phantoms with greater enclosure showed decreasing lithotripsy efficacy with 94±11%, 64±21%, and 13±2% breakage in basket, PVC, and anatomic phantom models, respectively. The time course of stone breakage was linear for all stone types except calcite, which demonstrated rapid breakage in the first 10 min followed by a prolonged delay to treatment completion. Stone breakage in 2:1 Begostone more closely mimicked COM stones compared to 4:1 Begostone, despite the latter having closer reported acoustic properties to COM. All UA stones were completely treated in 10 min.

Conclusions

The choice of model and environmental conditions can significantly affect lithotripsy results, and should be considered in in vitro lithotripsy studies. Partial water degassing at body temperature, realistic kidney phantoms, and appropriate stone models will help in vitro results better reflect clinical outcomes.

Funding

Acknowledge NIH DK043881, DK104854