title: Improving the lens design and performance of a contemporary electromagnetic shock wave lithotripter.
abstract: The efficiency of shock wave lithotripsy (SWL), a noninvasive first-line therapy for millions of nephrolithiasis patients, has not improved substantially in the past two decades, especially in regard to stone clearance. Here, we report a new acoustic lens design for a contemporary electromagnetic (EM) shock wave lithotripter, based on recently acquired knowledge of the key lithotripter field characteristics that correlate with efficient and safe SWL. The new lens design addresses concomitantly three fundamental drawbacks in EM lithotripters, namely, narrow focal width, nonidealized pulse profile, and significant misalignment in acoustic focus and cavitation activities with the target stone at high output settings. Key design features and performance of the new lens were evaluated using model calculations and experimental measurements against the original lens under comparable acoustic pulse energy (E+) of 40 mJ. The -6-dB focal width of the new lens was enhanced from 7.4 to 11 mm at this energy level, and peak pressure (41 MPa) and maximum cavitation activity were both realigned to be within 5 mm of the lithotripter focus. Stone comminution produced by the new lens was either statistically improved or similar to that of the original lens under various in vitro test conditions and was significantly improved in vivo in a swine model (89% vs. 54%, P = 0.01), and tissue injury was minimal using a clinical treatment protocol. The general principle and associated techniques described in this work can be applied to design improvement of all EM lithotripters.
authors.affiliation: Division of Urologic Surgery and Department of Pathology, Duke University Medical Center, Durham, NC 27710.
authors.forename: Andreas
authors.initials: A
authors.lastname: Neisius
authors.forename: Nathan B
authors.initials: NB
authors.lastname: Smith
authors.forename: Georgy
authors.initials: G
authors.lastname: Sankin
authors.forename: Nicholas John
authors.initials: NJ
authors.lastname: Kuntz
authors.forename: John Francis
authors.initials: JF
authors.lastname: Madden
authors.forename: Daniel E
authors.initials: DE
authors.lastname: Fovargue
authors.forename: Sorin
authors.initials: S
authors.lastname: Mitran
authors.forename: Michael Eric
authors.initials: ME
authors.lastname: Lipkin
authors.forename: Walter 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; D055590:Electromagnetic Phenomena; D004867:Equipment Design; D005260:Female; D007909:Lenses; D008096:Lithotripsy / Q000295:instrumentation*; D009038:Motion; D012119:Respiration; D012867:Skin / Q000473:pathology; D034421:Sus scrofa
keywords: electromagnetic lithotripter; lens modification; stone fragmentation