Neisius A et al, 2014: Improving the lens design and performance of a contemporary electromagnetic shock wave lithotripter
Neisius A, Smith NB, Sankin G, Kuntz NJ, Madden JF, Fovargue DE, Mitran S, Lipkin ME, Simmons WN, Preminger GM, Zhong P
Division of Urologic Surgery and Department of Pathology, Duke University Medical Center, Durham, NC 27710
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.
Proc Natl Acad Sci U S A. 2014 Apr 1;111(13):E1167-75. doi: 10.1073/pnas.1319203111. Epub 2014 Mar 17.
PMID:24639497[PubMed - in process]
PMCID:PMC3977262[Available on 2014/10/1]. FREE ARTICLE
This is the second paper dealing with a new lens design for an electromagnetic lithotripter.
See also previous review: 70. Smith NB et al, 2013: A heuristic model of stone comminution in shock wave lithotripsy.
It is motivated by the honourable ambition to improve performance of contemporary SWL devices with respect to safety and efficiency in order to achieve as good or better results as the legendary HM3. All approaches to develop further[sih1] shock wave technology are welcome and necessary to keep the acceptance level of SWL high. However, is the reported lens modification really the fundamental progress expected?
It is a modified version of shock wave delivery requiring almost 50% more of primary energy to achieve similar fragmentation efficiency (new lens 93±4% vs. old lens 93±3%). Only at positions laterally out of focus (10 mm) the new lens system provides slightly increased fragmentation efficiency (new lens 38±9% vs. old lens 27±8% with P=0.02). The widened focal area might be beneficial also in case of normal respiratory excursions (D=15 mm) with efficiencies of 82±4% (new lens) vs. 71±86% (old lens).
In vivo stone comminution of the new lens also shows some improvement (72.8±21. 4% vs. 63.6±21.8% with P=0.06). Side effects are considered minor.
The decisive open question is whether or not fragmentation can be increased while side effects can be reduced or at least kept as low as before. Otherwise, a slight increase of primary energy would provide higher fragmentation efficiency with the old lens system as well.
We wait for clinical results with higher patient numbers in particular with respect to side effects.