Assessment of a Modified Acoustic Lens for Electromagnetic Shock Wave Lithotripters in a Swine Model

Abstract

Purpose

The acoustic lens of the Siemens Modulariselectromagnetic (EM)shock wave lithotripter has been modified to produce a pressure waveform and focal zone more closely resembling that of the original Dornier HM3 device. Herein, we assess the newly designed acoustic lens in vivo in an animal model.

Materials and Methods

Stone fragmentation and tissue injury produced by theoriginal and modified lenses of a Siemens lithotripter were evaluated in a swine model under equivalent acoustic pulse energy (~45 mJ) at 1 Hz pulse repetition frequency.Stone fragmentation was determined by the weight percent of stone fragments less than 2mm. For tissue injury assessment, shock wave-treated kidneys were perfused, dehydrated, cast in paraffin wax and sectioned. Digital images were captured every 120 μm and processed to determine the functional renal volume damage.

Results

After 500 shocks, stone fragmentation efficiency produced by the original and modified lenses was 48 ± 12%and 52 ± 17%(p=0.60), respectively. However, after 2000 shocks, the modified lens showed significantly improved stone fragmentation of86 ± 10%, compared to 72 ± 12% for the original lens (p=0.02). Tissue injury caused by the original and modified lenses was minimal at 0.57± 0.44% and 0.25 ± 0.25% (p=0.27), respectively.

Conclusions

With lens modification, the Siemens Modularis lithotripterdemonstrates significantly improved stone fragmentationwith minimal tissue injuryat clinically relevant acoustic pulse energy.This new lens design could potentially be retrofitted to existing lithotripters, thereby improving the effectiveness of EM lithotripters.

http://www.jurology.com/article/S0022-5347(13)00350-9/abstract