HOLLYWOOD, FL USA (UroToday.com) - 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 that of the Dornier HM3.
In this study, we sought to determine the comminution efficiency of the modified lens following a clinical therapy regime and compared the results to comminution produce by the original lens in a swine model.
Materials and Methods: Using the maximum energy level (E+ = 44 mJ) that is safe for lithotripsy (i.e., without formation of gross hematoma), we compared stone comminution produced by the original and modified lenses in vivo using hard cylindrical Begostones (5 x 10 mm), surgically implanted in swine kidneys. A clinical protocol with a soft ramping scheme was used to deliver 3000 shock waves to each kidney using a pulse repetition frequency of 1.5 Hz, leading to a total accumulated energy of 112.84 J. Following lithotripsy, kidneys were harvested, dissected, all visible stone fragments were collected, dried and filtered with standard sieves with decreasing mesh size of 4, 2.8, and 2 mm, respectively. Final comminution efficiencies were determined by the percentage (by weight) of fragments less than 2 mm. 
An unpaired two−tailed student’s t−test was used to compare fragmentation results.
Results: At E+ = 44 mJ, the modified lens (12 renal units) showed a comminution efficiency of 72.8% (±21.4%) compared to 63.6% (±21.8%) for the original lens (10 renal units) overall (p=0.058). When considering stones not trapped by the ureteral stent loop with spread < 2 cm, comminution efficiency was 88.8% (±10.9%) for the modified lens vs 54.1% (±23.3%) for the original lens (p=0.013).
Conclusions: With our latest lens modification the electromagnetic lithotripter demonstrates better stone comminution under a clinically relevant energy setting and treatment protocol when compared to the original lens. This lens modification could be retrofitted to most electromagnetic lithotripters, thereby improving efficiency of clinical stone fragmentation.
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 Walter Simmons,2 Glenn Preminger,3 and Pei Zhong6 at the 78th Annual Meeting of the Southeastern Section of the AUA - March 20 - 23, 2014 - Hollywood, Florida USA
1 University Medical Center Mainz, Department of Urology, Mainz, Germany;
2 Department of Mechanical Engineering and Materials Science, Duke University, Durham, NC, USA;
3 Division of Urologic Surgery, Duke University Medical Center, Durham, NC, USA;
4 Universidad Católica de Chile. Santiago, Chile;
5 Duke Clinical Research Institute, Division of Urologic Surgery, Duke University Medical Center, Durham, NC, USA;
6 Department of Mechanical Engineering and Materials Science, Division of Urologic Surgery, Duke University, Durham, NC, USA