Enhanced High-Rate Shockwave Lithotripsy Stone Comminution in an In Vivo Porcine Model Using Acoustic Bubble Coalescence

Abstract

Cavitation plays a significant role in the efficacy of stone comminution during shockwave lithotripsy (SWL). Although cavitation on the surface of urinary stones helps to improve fragmentation, cavitation bubbles along the propagation path may shield or block subsequent shockwaves (SWs) and potentially induce collateral tissue damage. Previous in vitro work has shown that applying low-amplitude acoustic waves after each SW can force bubbles to consolidate and enhance SWL efficacy. In this study, the feasibility of applying acoustic bubble coalescence (ABC) in vivo was tested. Model stones were percutaneously implanted and treated with 2500 lithotripsy SWs at 120 SW/minute with or without ABC. Comparing the results of stone comminution, a significant improvement was observed in the stone fragmentation process when ABC was used. Without ABC, only 25% of the mass of the stone was fragmented to particles <2 mm in size. With ABC, 75% of the mass was fragmented to particles <2 mm in size. These results suggest that ABC can reduce the shielding effect of residual bubble nuclei, resulting in a more efficient SWL treatment.

Keywords: acoustic bubble coalescence; extracorporeal shock wave lithotripsy; high rate SWL; in vivo; renal stone; shielding effect.

FIG. 1.

Experiment setup: the model stone implanted in the right kidney of the porcine model is targeted and treated by a laboratory electrohydraulic lithotripter patterned after Dornier HM3 along with a separate annular transducer array generating the ABC pulses. The water bolus is filled with degassed water with gas concentration below 10% saturation and contains a 15 cm cutout for direct coupling of sound from the water to the skin. The animal's vital signs, including oxygen saturation, heart rate, respiration, and core body temperature, were monitored throughout the experiment. ABC, acoustic bubble coalescence.

FIG. 2.

Acoustic pulse sequence for SWL and bubble coalescing. The SWL rate was 120 SW/minute interleaved with bubble coalescing pulses applied for duration of 16 millisecond. SW = shockwave; SWL = shockwave lithotripsy.

FIG. 3.

Typical results from normal SWL treatment (a, c) and SWL with ABC (b, d). Recovered fragments from treatments with normal SWL (c) were visibly larger than treatments with SWL and ABC (d).

FIG. 4.

Posttreatment stone fragment distribution normalized to initial stone mass for normal SWL and SWL combined with ABC. The distribution is significantly shifted toward smaller fragments for SWL with ABC.