title: Assessment of a modified acoustic lens for electromagnetic shock wave lithotripters in a swine model.
abstract: OBJECTIVE
  The acoustic lens of the Modularis electromagnetic shock wave lithotripter (Siemens, Malvern, Pennsylvania) was modified to produce a pressure waveform and focal zone more closely resembling that of the original HM3 device (Dornier Medtech, Wessling, Germany). We assessed the newly designed acoustic lens in vivo in an animal model.
  
  
  METHODS
  Stone fragmentation and tissue injury produced by the original and modified lenses of the Modularis lithotripter were evaluated in a swine model under equivalent acoustic pulse energy (about 45 mJ) at 1 Hz pulse repetition frequency. Stone fragmentation was determined by the weight percent of stone fragments less than 2 mm. To assess tissue injury, shock wave treated kidneys were perfused, dehydrated, cast in paraffin wax and sectioned. Digital images were captured every 120 μm and processed to determine functional renal volume damage.
  
  
  RESULTS
  After 500 shocks, the mean ± SD stone fragmentation efficiency produced by the original and modified lenses was 48% ± 12% and 52% ± 17%, respectively (p = 0.60). However, after 2,000 shocks, the modified lens showed significantly improved stone fragmentation compared to the original lens (mean 86% ± 10% vs 72% ± 12%, p = 0.02). Tissue injury caused by the original and modified lenses was minimal at a mean of 0.57% ± 0.44% and 0.25% ± 0.25%, respectively (p = 0.27).
  
  
  CONCLUSIONS
  With lens modification the Modularis lithotripter demonstrates significantly improved stone fragmentation with minimal tissue injury at a clinically relevant acoustic pulse energy. This new lens design could potentially be retrofitted to existing lithotripters, improving the effectiveness of electromagnetic lithotripters.
authors.affiliation: Division of Urologic Surgery, Duke University, Durham, North Carolina 27708, USA.
authors.forename: John G
authors.initials: JG
authors.lastname: Mancini
authors.forename: Andreas
authors.initials: A
authors.lastname: Neisius
authors.forename: Nathan
authors.initials: N
authors.lastname: Smith
authors.forename: Georgy
authors.initials: G
authors.lastname: Sankin
authors.forename: Gaston M
authors.initials: GM
authors.lastname: Astroza
authors.forename: Michael E
authors.initials: ME
authors.lastname: Lipkin
authors.forename: W Neal
authors.initials: WN
authors.lastname: Simmons
authors.forename: Glenn M
authors.initials: GM
authors.lastname: Preminger
authors.forename: Pei
authors.initials: P
authors.lastname: Zhong
mesh_terms: D000818:Animals; D004195:Disease Models, Animal; D004574:Electromagnetic Fields; D004867:Equipment Design; D004869:Equipment Safety; D005260:Female; D007669:Kidney Calculi / Q000628:therapy*; D008096:Lithotripsy / Q000295:instrumentation* / Q000379:methods; D033401:Microscopy, Acoustic / Q000295:instrumentation* / Q000379:methods; D012680:Sensitivity and Specificity; D034421:Sus scrofa; D013552:Swine
keywords: AR; EH; EM; PRF; SWL; area ratio; electrohydraulic; electromagnetic; equipment and supplies; kidney; kidney calculi; lenses; lithotripsy; pulse repetition frequency; shock wave lithotripsy