Experimentally validated multiphysics computational model of focusing and shock wave formation in an electromagnetic lithotripter

Fovargue, Daniel; Mitran, Sorin; Smith, Nathan B.; Sankin, Georgy; Simmons, W. Neal; Zhong, Pei

doi:10.1121/1.4812881

Cited by 9 publications

(11 citation statements)

References 33 publications

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“…The measured location of peak jp − j is ∼30 mm prefocal with the original lens and ≥60 mm with the new lens, although a minimum in jp − j occurs ∼5 mm prefocally, which corresponds to the location of strongest acoustic cancellation effects from in situ pulse superposition. The general trend in pressure distribution and acoustic focal shift has been confirmed by simulation results from a multiphysics model of shock wave focusing through the original and new lenses (30). In the case of the original lens, the multiphysics model was used to estimate prefocal shift (∼30 mm) at a high source voltage (18.1 kV) where FOPH measurements became impractical owing to interference from strong prefocal cavitation activity.…”

Section: Resultsmentioning

confidence: 67%

“…To estimate the acoustic focusing distance of the new lens at various source voltages, a multiphysics computational model of wave propagation for EM shock wave lithotripters was used (see SI Materials and Methods for further details and Fig. 2 C and D for representative computational results) (30). After determination of critical geometric parameters from pilot experiments and modeling, the new lens was machined from a 6-inch-diameter solid cylinder of Rexolite 1422 cross-linked polystyrene (SI Materials and Methods).…”

Section: Methodsmentioning

confidence: 99%

See 1 more Smart Citation

Improving the lens design and performance of a contemporary electromagnetic shock wave lithotripter

Neisius

Smith

Sankin

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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The efficiency of shock wave lithotripsy (SWL), a noninvasive firstline 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. electromagnetic lithotripter | lens modification | stone fragmentation

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Section: Resultsmentioning

confidence: 67%

Section: Methodsmentioning

confidence: 99%

Improving the lens design and performance of a contemporary electromagnetic shock wave lithotripter

Neisius

Smith

Sankin

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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“…Relationships between stone size and comminution efficiency were also investigated by numerical simulations using the axisymmetric elasticity solver within the BEARCLAW finite- volume code (Fovargue et al 2013). This is a high-resolution method that uses second-order Riemann solvers and flux limiters (Langseth 1995) to accurately capture sharp gradients, as produced by LSWs with fast rise time or obtained by sharp changes in material properties.…”

Section: Methodsmentioning

confidence: 99%

“…2a). Simulations were carried out for both radially uniform pressure pulses, and validated radial pressure distributions produced by the Siemens Modularis lithotripter (Fovargue et al 2013). The radially uniform incident LSW pulses allow us to assess the effect of stone size on resultant stress field without the influence of the lithotripter focal width (Cleveland and Sapozhnikov 2005).…”

Section: Methodsmentioning

confidence: 99%

Effects of Stone Size on the Comminution Process and Efficiency in Shock Wave Lithotripsy

Zhang

Nault

Mitran

et al. 2016

Ultrasound in Medicine & Biology

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The effects of stone size on the process and comminution efficiency in shock wave lithotripsy (SWL) are investigated by experiments, numerical simulations, and scale analysis. Cylindrical BegoStone phantoms with approximately equal height and diameter of either 4-, or 7- or 10-mm, in a total aggregated mass of about 1.5 g, were treated in an electromagnetic shock wave lithotripter field. The resultant stone comminution (SC) was found to correlate closely with the average peak pressure, P+(avg), incident on the stones. The P+(avg) threshold to initiate stone fragmentation in water increased from 7.9 to 8.8 to 12.7 MPa, respectively, when the stone size decreased from 10 to 7 to 4 mm. Similar changes in the P+(avg) threshold were observed for the 7- and 10-mm stones treated in 1,3-butanediol where cavitation is suppressed, suggesting that the observed size dependency is due to changes in stress distribution within different size stones. Moreover, the slope of the correlation curve between SC and ln(Pfalse‒+(avg)) in water increased with decreasing stone size, while the opposite trend was observed in 1,3-butanediol. The progression of stone comminution in SWL showed a size-dependency with the 7- and 10-mm stones fragmented into progressively smaller pieces while a significant portion (> 30%) of the 4-mm stones were stalemated within the size range of 2.8 ~ 4 mm even after 1,000 shocks. Analytical scaling considerations suggest size-dependent fragmentation behaviour, a hypothesis further supported by numerical model calculations that exhibit changing patterns of constructive and destructive wave interference, and thus variations in the maximum tensile stress or stress integral produced in cylindrical and spherical stone of different sizes.

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“…Previous computational efforts on simulating SWL have mostly been focused on either the fluid part of the problem, particularly the flow dynamics of cavitation bubbles interacting with shock waves and rigid solids 11,12,[24][25][26][27][28][29] or the solid part, particularly the evolution of stress in a stone or soft tissue under LSW loading. [30][31][32] For example, in the study of Johnsen and Colonius, 11 the authors applied a finite difference 2-phase flow solver to simulate shock-induced collapse of a bubble near a kidney stone, in which the stone is rigidly fixed.…”

Section: Introductionmentioning

confidence: 99%

Multiphase fluid‐solid coupled analysis of shock‐bubble‐stone interaction in shockwave lithotripsy

Wang

2017

Numer Methods Biomed Eng

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A novel multiphase fluid-solid-coupled computational framework is applied to investigate the interaction of a kidney stone immersed in liquid with a lithotripsy shock wave (LSW) and a gas bubble near the stone. The main objective is to elucidate the effects of a bubble in the shock path to the elastic and fracture behaviors of the stone. The computational framework couples a finite volume 2-phase computational fluid dynamics solver with a finite element computational solid dynamics solver. The surface of the stone is represented as a dynamic embedded boundary in the computational fluid dynamics solver. The evolution of the bubble surface is captured by solving the level set equation. The interface conditions at the surfaces of the stone and the bubble are enforced through the construction and solution of local fluid-solid and 2-fluid Riemann problems. This computational framework is first verified for 3 example problems including a 1D multimaterial Riemann problem, a 3D shock-stone interaction problem, and a 3D shock-bubble interaction problem. Next, a series of shock-bubble-stone-coupled simulations are presented. This study suggests that the dynamic response of a bubble to LSW varies dramatically depending on its initial size. Bubbles with an initial radius smaller than a threshold collapse within 1 μs after the passage of LSW, whereas larger bubbles do not. For a typical LSW generated by an electrohydraulic lithotripter (p = 35.0MPa, p =- 10.1MPa), this threshold is approximately 0.12mm. Moreover, this study suggests that a noncollapsing bubble imposes a negative effect on stone fracture as it shields part of the LSW from the stone. On the other hand, a collapsing bubble may promote fracture on the proximal surface of the stone, yet hinder fracture from stone interior.

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Experimentally validated multiphysics computational model of focusing and shock wave formation in an electromagnetic lithotripter

Cited by 9 publications

References 33 publications

Improving the lens design and performance of a contemporary electromagnetic shock wave lithotripter

Improving the lens design and performance of a contemporary electromagnetic shock wave lithotripter

Effects of Stone Size on the Comminution Process and Efficiency in Shock Wave Lithotripsy

Multiphase fluid‐solid coupled analysis of shock‐bubble‐stone interaction in shockwave lithotripsy

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