SES AUA 2014 - Poster and Abstract: Energy and pulse repetition frequency dependent tissue injury produced by a modified acoustic lens for electromagnetic lithotripters

HOLLYWOOD, FL USA ( - Purpose: The acoustic lens of a Siemens Modularis electromagnetic shock wave lithotripter has been further modified to reduce pre−focal cavitation while generating a pressure waveform and broad focal zone mimicking the Dornier HM3 electrohydraulic device.

We sought to determine the threshold for the maximum acoustic energy which can be safely applied to a kidney under clinically relevant treatment protocols, and the dependency of tissue injury on pulse repetition frequency (PRF).

aua sesMaterials and Methods: Tissue injury (TI) produced by the original and modified lenses in a swine model were first evaluated starting from the highest output level to determine the threshold energy for safe lithotripsy. Thereafter, TI was assessed under an effective acoustic pulse energy for the leading compressive wave (E+) of 44 mJ. A clinical protocol with a soft ramping scheme was used to deliver 3000 shock waves to each kidney using a PRF of 1.0 and 1.5 Hz, leading to a total accumulated energy of 112.84 J. Following lithotripsy, kidneys were perfused, harvested, dehydrated, cast in paraffin wax, and sectioned. Photographic images were taken every 120 um and analyzed to determine the functional renal volume (FRV) damage.

sesaua poster 54 thumbResults: Gross subcapsular hematomas were produced by both the original and modified lenses at E+ of 51 mJ. Using E+ of 44 mJ, the modified lens showed quantitatively macroscopic tissue injury (subcapsular hematoma) in 1/6 renal units (17%) in the 1.5 Hz group. No macroscopic tissue injury was detected in the 1.0 Hz group (0/6 renal units). After processing of the digitalized images TI was detected in 0.432% (±0.51%) of the FRV (with a maximum level of 1.324% in the kidney with the gross hematoma) in the 1.5 Hz group and in 0.009% (±0.015%) of the FRV in the 1 Hz group (p=0.025), respectively.

Conclusions: This study demonstrates that the energy threshold for gross TI of the modified lens is comparable to the original lens. Our data further confirms that the initiation of TI depends on acoustic pulse energy, and the extent of TI depends on the total accumulated acoustic energy delivered to a kidney, as well as on PRF. Overall, our results suggest that a rational design of treatment strategies to minimize tissue injury in SWL is warranted.

Presented by: Andreas Neisius,1 Nathan Smith,2 Nicholas Kuntz,3 Tim Schykowski,3 Gaston Astroza,4 Fernando Cabrera,3 Ramy Youssef,3 Richard Shin MD,3 Charles Scales,5 Michael Lipkin,3 Michael Gustafson,2 Walter Simmons,2 Glenn Preminger,2 and Pei Zhong6 at the 78th Annual Meeting of the Southeastern Section of the AUA - March 20 - 23, 2014 - Hollywood, Florida USA

1University Medical Center Mainz, Department of Urology, Mainz, Germany;
2Department of Mechanical Engineering and Materials Science, Duke University, Durham, NC, USA;
3Division of Urologic Surgery, Duke University Medical Center, Durham, NC, USA;
4Universidad Católica de Chile. Santiago, Chile;
5Duke Clinical Research Institute, Division of Urologic Surgery, Duke University Medical Center, Durham, NC, USA;
6Department of Mechanical Engineering and Materials Science, Division of Urologic Surgery, Duke University, Durham, NC, USA