Stone Comminution Research Articles

V9-05 A SIMPLIFIED TECHNIQUE FOR PERFORMANCE OF FLUOROLESS URETEROSCOPY

INTRODUCTION AND OBJECTIVES: Percutaneous nephrolithotomy (PCNL) remains a challenging procedure associated with significant potential for patient morbidity. In an attempt to decrease the morbidity of PCNL, we have developed a novel technique employing direct visualization with ureteroscopy to decrease ambiguity associated with fluoroscopy guidance, while eliminating ionizing radiation exposure. In this video, we demonstrate PCNL techniques that obviate the need for fluoroscopy. METHODS: This video demonstrates fluoroless PCNL in a 56 year-old female with large left renal stone burden (>4 cm). The patient was positioned prone and split-leg. Utilizing visual and tactile cues, a super-stiff and standard guidewire were placed from below using a flexible cystoscope. Using flexible ureteroscopy, the ideal calyx for access was selected. Under ultrasound guidance, an access needle was placed into the selected calyx, which was directly visualized on ureteroscopy. With the aid of a stone basket, an access wire was pulled into the ureter to allow for subsequent exchange to a super-stiff guidewire. Under direct visualization with the ureteroscope, the balloon and access sheath were positioned. The ureteroscope was left with the tip occluding the ureteropelvic junction to prevent distal migration of fragments. Stone comminution was accomplished with an ultrasonic lithotripter. Stone-free status was assured intraoperatively using a combination of flexible nephroscopy and ureteroscopy. A nephrostomy tube and multipurpose angled ureteral catheter were placed under direct vision ureteroscopically to conclude the procedure. RESULTS: Operative time was 4 hours 36 minutes. Estimated blood loss was <50 mL. On post-operative day one, a 15 mAs low-dose CT (<1 mSv) demonstrated stone-free status. CONCLUSIONS: This technique combines the methods of many pioneering endourologic surgeons in a unique way to perform PCNL under direct visualization. We believe this technique offers significant promise both by eliminating uncertainties encountered when operating under fluoroscopic guidance and reducing the risk of radiation exposure to patients and operating room staff.

V9-04 DIRECT VISUALIZATION PERCUTANEOUS NEPHROLITHOTOMY WITHOUT FLUOROSCOPY

INTRODUCTION AND OBJECTIVES: Percutaneous nephrolithotomy (PCNL) remains a challenging procedure associated with significant potential for patient morbidity. In an attempt to decrease the morbidity of PCNL, we have developed a novel technique employing direct visualization with ureteroscopy to decrease ambiguity associated with fluoroscopy guidance, while eliminating ionizing radiation exposure. In this video, we demonstrate PCNL techniques that obviate the need for fluoroscopy. METHODS: This video demonstrates fluoroless PCNL in a 56 year-old female with large left renal stone burden (>4 cm). The patient was positioned prone and split-leg. Utilizing visual and tactile cues, a super-stiff and standard guidewire were placed from below using a flexible cystoscope. Using flexible ureteroscopy, the ideal calyx for access was selected. Under ultrasound guidance, an access needle was placed into the selected calyx, which was directly visualized on ureteroscopy. With the aid of a stone basket, an access wire was pulled into the ureter to allow for subsequent exchange to a super-stiff guidewire. Under direct visualization with the ureteroscope, the balloon and access sheath were positioned. The ureteroscope was left with the tip occluding the ureteropelvic junction to prevent distal migration of fragments. Stone comminution was accomplished with an ultrasonic lithotripter. Stone-free status was assured intraoperatively using a combination of flexible nephroscopy and ureteroscopy. A nephrostomy tube and multipurpose angled ureteral catheter were placed under direct vision ureteroscopically to conclude the procedure. RESULTS: Operative time was 4 hours 36 minutes. Estimated blood loss was <50 mL. On post-operative day one, a 15 mAs low-dose CT (<1 mSv) demonstrated stone-free status. CONCLUSIONS: This technique combines the methods of many pioneering endourologic surgeons in a unique way to perform PCNL under direct visualization. We believe this technique offers significant promise both by eliminating uncertainties encountered when operating under fluoroscopic guidance and reducing the risk of radiation exposure to patients and operating room staff.

PD37-04 BALL-TIP HOLMIUM LASER FIBER: IN VITRO STONE COMMINUTION AND FIBER TIP DEGRADATION

You have accessJournal of UrologyStone Disease: New Technology II1 Apr 2014PD37-04 BALL-TIP HOLMIUM LASER FIBER: IN VITRO STONE COMMINUTION AND FIBER TIP DEGRADATION Richard Shin, Jaclyn Lautz, Fernando Cabrera, Zachariah Goldsmith, Nicholas Kuntz, Ramy Youssef, Andreas Neisius, Charles Scales, Michael Ferrandino, Pei Zhong, Walter Simmons, Glenn Preminger, and Michael Lipkin Richard ShinRichard Shin More articles by this author , Jaclyn LautzJaclyn Lautz More articles by this author , Fernando CabreraFernando Cabrera More articles by this author , Zachariah GoldsmithZachariah Goldsmith More articles by this author , Nicholas KuntzNicholas Kuntz More articles by this author , Ramy YoussefRamy Youssef More articles by this author , Andreas NeisiusAndreas Neisius More articles by this author , Charles ScalesCharles Scales More articles by this author , Michael FerrandinoMichael Ferrandino More articles by this author , Pei ZhongPei Zhong More articles by this author , Walter SimmonsWalter Simmons More articles by this author , Glenn PremingerGlenn Preminger More articles by this author , and Michael LipkinMichael Lipkin More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2014.02.2022AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES Advancing a standard laser fiber through a fully deflected ureteroscope can result in significant damage to the delicate working channel, resulting in significant repair costs. A new ball-tip holmium laser fiber (Flexiva TracTip - Boston Scientific) was designed to atraumatically pass through a deflected ureteroscope. We evaluated the stone comminution capabilities and tip degradation of this fiber in an in vitro model. METHODS A 200 μm ball-tip (BT) fiber and standard fiber (SF) (Flexiva - Boston Scientific) were compared by delivering energy to a Begostone over a constant surface area controlled by a stage controller and 3 dimensional positioning system. Laser settings were 0.2J/50Hz, 0.6J/6Hz, 0.8J/8Hz, and 1J/10Hz. Fiber tip degradation was measured at 1 kJ and 4 kJ of delivered energy. Fiber-stone contact was adjusted every 1 kJ to account for any loss in length. Comminution efficiency was determined by measuring stone weight loss following lithotripsy at each energy setting. ANOVA or Kruskal Wallace test was used for multiple groups, and post hoc tests with Bonferroni correction were then applied (t-test, Wilcoxon). RESULTS A total of 5 virgin fibers were used to test each condition. Tip degradation by 1 kJ with all energy settings and 4 kJ at 0.2J/50Hz was minimal for both fibers without significant differences. By 4 kJ, tip degradation was less overall for the BT and maximal for the SF at 1J/10Hz (Table). Comminution was found to increase with pulse energy for both BT and SF fibers up to the 0.8J/8Hz setting (p < 0.003). No significant differences were found between 0.8J/8Hz and 1J/10Hz or between BT and SF fibers at any energy setting (Figure). CONCLUSIONS The ball-tip fiber exhibits similar comminution efficiency to a standard holmium laser fiber with minimal tip degradation at clinically relevant laser settings in our in vitro model. The new tip design may provide an advantage in access maneuverability without loss of performance. Further in vivo studies are warranted to validate these objective findings. Standard fiber (SF) and ball-tip (BT) fiber tip degradation at 1 kJ and 4 kJ (Median with IQR) Setting Energy SF tip degradation (mm) BT tip degradation (mm) P value 0.2J/50Hz 1 kJ 0 (-0.1 - 0.03) -0.02 (-0.05 - 0.02) 1 4 kJ 0 (-0.12 - 0.06) 0.07 (0.01 - 0.1) 0.207 0.6J/6Hz 1 kJ 0 (-0.08 - 0.05) 0 (-0.05 - 0.1) 0.747 4 kJ 0.16 (0.1 - 0.2) 0.15 (0.02 - 0.56) 0.599 0.8J/8Hz 1 kJ 0.05 (0 - 0.08) 0.1 (0 - 0.1) 0.576 4 kJ 0.25 (0.23 - 0.28) 0.1 (0.03 - 0.23) 0.112 1J/10Hz 1 kJ 0 (-0.05 - 0) 0.05 (0.02 - 0.1) 0.084 4 kJ 0.3 (0.2 - 1.35) 0.08 (0 - 0.2) 0.036 © 2014FiguresReferencesRelatedDetailsCited byKronenberg P and Traxer O (2018) Lithotripsy Performance of Specially Designed Laser Fiber TipsJournal of Urology, VOL. 195, NO. 5, (1606-1612), Online publication date: 1-May-2016. Volume 191Issue 4SApril 2014Page: e947 Advertisement Copyright & Permissions© 2014MetricsAuthor Information Richard Shin More articles by this author Jaclyn Lautz More articles by this author Fernando Cabrera More articles by this author Zachariah Goldsmith More articles by this author Nicholas Kuntz More articles by this author Ramy Youssef More articles by this author Andreas Neisius More articles by this author Charles Scales More articles by this author Michael Ferrandino More articles by this author Pei Zhong More articles by this author Walter Simmons More articles by this author Glenn Preminger More articles by this author Michael Lipkin More articles by this author Expand All Advertisement Advertisement PDF downloadLoading ...

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

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.

A non-axisymmetric, elongated pressure distribution in the lithotripter focal plane enhances stone comminution in vitro during simulated respiratory motion

A challenge in clinical shock wave lithotripsy (SWL) is stone translation due to a patient’s respiratory motion, in a direction perpendicular to shockwave propagation, which may negatively affect stone comminution while increasing the risk of tissue injury. We have developed a method using external masks and a modified lens geometry to transform the axisymmetric pressure distribution in the focal plane of an electromagnetic lithotripter into a non-axisymmetric elliptical distribution. At equivalent acoustic pulse energy (46 mJ), the peak pressure was reduced from 44 MPa to 38 MPa while the −6 dB focal width was increased from 7.4 mm for the original to 11.7 mm (major axis) and 7.9 mm (minor axis) of the modified field. In vitro stone comminution was performed in a tube holder (d = 14 mm) using a translation pattern with 12 breaths per minute and 15 mm in excursion distance. Stone comminution after 1000 shocks are 71.2 ± 4.4% and 65.2 ±8.3% (p &amp;lt; 0.05) along the major- and minor-axis of the modified field, respectively, compared to 62.6 ± 7.2% for the original axisymmetric field. These results suggest that an elongated pressure field aligned along the direction of stone motion may enhance stone comminution in SWL. [Work supported by the NIH and the NSF GRFP.]

Shockwave tensile phase transmission depends on the gas concentration of the coupling medium

Previous research shows that a shockwave’s tensile phase can be strongly attenuated as a function of gas concentration in the coupling medium. Here, we seek to elucidate the relationship between tensile attenuation and gas concentration via pressure measurements at the focus and highspeed imaging. By performing in vitro experiments with water of varying gas concentrations (2.05 mg/L, 4.30 mg/L, and 6.50 mg/L), the negative impulsive pressure is correlated to the density of the bubble cloud that occurs in the beampath. It is found that for gas contents below 4 mg/L the bubble cloud remains sparse and the shockwave’s tensile phase is successfully transmitted with no loss in impulsive pressure. For gas contents 4 mg/L and above the bubble cloud becomes highly dense and prevents transmission with up to a 75% loss in impulsive pressure. Corresponding stone comminution experiments show that the treatment efficiency sharply decreases with increasing gas concentration. These results underlie the importance of degassing the water used in the coupling medium before treatment.

Acoustic Bubble Removal to Enhance SWL Efficacy at High Shock Rate: An In Vitro Study

Rate-dependent efficacy has been extensively documented in shock wave lithotripsy (SWL) stone comminution, with shock waves (SWs) delivered at a low rate producing more efficient fragmentation in comparison to those delivered at high rates. Cavitation is postulated to be the primary source underlying this rate phenomenon. Residual bubble nuclei that persist along the axis of SW propagation can drastically attenuate the waveform's negative phase, decreasing the energy which is ultimately delivered to the stone and compromising comminution. The effect is more pronounced at high rates, as residual nuclei have less time to passively dissolve between successive shocks. In this study, we investigate a means of actively removing such nuclei from the field using a low-amplitude acoustic pulse designed to stimulate their aggregation and subsequent coalescence. To test the efficacy of this bubble removal scheme, model kidney stones were treated in vitro using a research electrohydraulic lithotripter. SWL was applied at rates of 120, 60, or 30 SW/min with or without the incorporation of bubble removal pulses. Optical images displaying the extent of cavitation in the vicinity of the stone were also collected for each treatment. Results show that bubble removal pulses drastically enhance the efficacy of stone comminution at the higher rates tested (120 and 60 SW/min), while optical images show a corresponding reduction in bubble excitation along the SW axis when bubble removal pulses are incorporated. At the lower rate of 30 SW/min, no difference in stone comminution or bubble excitation was detected with the addition of bubble removal pulses, suggesting that remnant nuclei had sufficient time for more complete dissolution. These results corroborate previous work regarding the role of cavitation in rate-dependent SWL efficacy, and suggest that the effect can be mitigated via appropriate control of the cavitation environment surrounding the stone.

A heuristic model of stone comminution in shock wave lithotripsy

A heuristic model is presented to describe the overall progression of stone comminution in shock wave lithotripsy (SWL), accounting for the effects of shock wave dose and the average peak pressure, P+(avg), incident on the stone during the treatment. The model is developed through adaptation of the Weibull theory for brittle fracture, incorporating threshold values in dose and P+(avg) that are required to initiate fragmentation. The model is validated against experimental data of stone comminution from two stone types (hard and soft BegoStone) obtained at various positions in lithotripter fields produced by two shock wave sources of different beam width and pulse profile both in water and in 1,3-butanediol (which suppresses cavitation). Subsequently, the model is used to assess the performance of a newly developed acoustic lens for electromagnetic lithotripters in comparison with its original counterpart both under static and simulated respiratory motion. The results have demonstrated the predictive value of this heuristic model in elucidating the physical basis for improved performance of the new lens. The model also provides a rationale for the selection of SWL treatment protocols to achieve effective stone comminution without elevating the risk of tissue injury.

1821 A PROSPECTIVE RANDOMIZED STUDY COMPARING THE EFFECT OF ESCALATING AND FIXED VOLTAGE TREATMENT ON STONE COMMINUTION AND RENAL INJURY DURING ESWL

You have accessJournal of UrologyStone Disease: SWL, Ureteroscopy or Percutaneous Stone Removal (III)1 Apr 20131821 A PROSPECTIVE RANDOMIZED STUDY COMPARING THE EFFECT OF ESCALATING AND FIXED VOLTAGE TREATMENT ON STONE COMMINUTION AND RENAL INJURY DURING ESWL Nabankur Ghosh, Soumendra Nath Mandal, Sudip Bakshi, and Dilip Karmakar Nabankur GhoshNabankur Ghosh Kolkata, India More articles by this author , Soumendra Nath MandalSoumendra Nath Mandal Kolkata, India More articles by this author , Sudip BakshiSudip Bakshi Kolkata, India More articles by this author , and Dilip KarmakarDilip Karmakar Kolkata, India More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2013.02.2184AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES Extracorporeal Shock Wave Lithotripsy (ESWL) has become first line therapy for most renal stones. How ever, there is no clear cut guideline regarding optimal voltage delivery to maximize stone comminution with minimal renal injuries. We compared the stone comminution and renal injuries produced by fixed versus escalating voltage protocols through a prospective randomized comparative study. METHODS Between September 2011 and August 2012, total 40 patients were enrolled for our study ? 20 in each group (fixed versus escalating). All of them were undergone ESWL (Dornier Compact Sigma machine was used) according to our study protocol. In escalating voltage protocol group, 500 shocks in power 1, 500 shocks in power 2 and 1000 shocks in power 3 were delivered. In fixed voltage protocol, 2000 shocks were delivered in power 3. Position of the stone checked after every 250 shocks. Stone comminution was assessed with X-ray KUB after 1 month and 3 months. Renal injures were assessed with 24 hours urinary microalbumin and beta 2 microglobulin levels pre-procedure, immediately post procedure and 7 days after procedure. Standard statistical methods were used for data analysis. RESULTS Among the patients, M: F ratio was 2:1. Mean age was 38 years. Stone size ranges from 7 ? 15 mm. In escalating voltage group, 75% were stone free where in fixed voltage group, 72 % were stone free. There was significant difference between urinary microalbumin and beta 2 microglobulin levels both immediately post procedure and 7 days after procedure which were statistically significant. CONCLUSIONS Although there is no significant difference in stone comminution between the fixed and escalating voltage strategies, renal injuries are significantly less in escalating voltage strategy compared to fixed voltage strategy. © 2013 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 189Issue 4SApril 2013Page: e748-e749 Advertisement Copyright & Permissions© 2013 by American Urological Association Education and Research, Inc.MetricsAuthor Information Nabankur Ghosh Kolkata, India More articles by this author Soumendra Nath Mandal Kolkata, India More articles by this author Sudip Bakshi Kolkata, India More articles by this author Dilip Karmakar Kolkata, India More articles by this author Expand All Advertisement Advertisement PDF DownloadLoading ...

541 A prospective randomized study comparing the effect of escalating and fixed voltage treatment on stone comminution and renal injury during ESWL

541 A prospective randomized study comparing the effect of escalating and fixed voltage treatment on stone comminution and renal injury during ESWL

653 In vivo stone comminution produced by a modified acoustic lens for electromagnetic lithotripters

653 In vivo stone comminution produced by a modified acoustic lens for electromagnetic lithotripters

Controlled cavitation to augment SWL stone comminution: mechanistic insights in vitro

Stone comminution in shock wave lithotripsy (SWL) has been documented to result from mechanical stresses conferred directly to the stone, as well as the activity of cavitational microbubbles. Studies have demonstrated that the presence of this cavitation activity is crucial for stone subdivision; however, its exact role in the comminution process remains somewhat weakly defined, in part because it is difficult to isolate the cavitational component from the shock waves themselves. In this study, we further explored the importance of cavitation in SWL stone comminution through the use of histotripsy ultrasound therapy. Histotripsy was used to target model stones designed to mimic the mid-range tensile fracture strength of naturally occurring cystine calculi with controlled cavitation at strategic time points in the SWL comminution process. All SWL was applied at a peak positive pressure (p+) of 34 MPa and a peak negative pressure (p-) of 8 MPa; a shock rate of 1 Hz was used. Histotripsy pulses had a p- of 33 MPa and were applied at a pulse repetition frequency (PRF) of 100 Hz. Ten model stones were sonicated in vitro with each of five different treatment schemes: A) 10 min of SWL (600 shocks) with 0.7 s of histotripsy interleaved between successive shocks (totaling to 42 000 pulses); B) 10 min of SWL (600 shocks) followed by 10 min of histotripsy applied in 0.7-s bursts (1 burst per second, totaling to 42 000 pulses); C) 10 min of histotripsy applied in 0.7-s bursts (42 000 pulses) followed by 10 min of SWL (600 shocks); D) 10 min of SWL only (600 shocks); E) 10 min of histotripsy only, applied in 0.7-s bursts (42 000 pulses). Following sonication, debris was collected and sieved through 8-, 6-, 4-, and 2-mm filters. It was found that scheme D, SWL only, generated a broad range of fragment sizes, with an average of 14.9 ± 24.1% of the original stone mass remaining > 8 mm. Scheme E, histotripsy only, eroded the surface of stones to tiny particulate debris that was small enough to pass through the finest filter used in this study (<2 mm), leaving behind a single primary stone piece (>8 mm) with mass 85.1 ± 1.6% of the original following truncated sonication. The combination of SWL and histotripsy (schemes A, B, and C) resulted in a shift in the size distribution toward smaller fragments and complete elimination of debris > 8 mm. When histotripsy-controlled cavitation was applied following SWL (B), the increase in exposed stone surface area afforded by shock wave stone subdivision led to enhanced cavitation erosion. When histotripsy-controlled cavitation was applied before SWL (C), it is likely that stone surface defects induced by cavitation erosion provided sites for crack nucleation and accelerated shock wave stone subdivision. Both of these effects are likely at play in the interleaved therapy (A), although shielding of shock waves by remnant histotripsy microbubble nuclei may have limited the efficacy of this scheme. Nevertheless, these results demonstrate the important role played by cavitation in the stone comminution process, and suggest that the application of controlled cavitation at strategic time points can provide an adjunct to traditional SWL therapy.

Turbulent water coupling in shock wave lithotripsy

Previous studies have demonstrated that stone comminution decreases with increased pulse repetition frequency as a result of bubble proliferation in the cavitation field of a shock wave lithotripter (Pishchalnikov et al 2011 J. Acoust. Soc. Am. 130 EL87–93). If cavitation nuclei remain in the propagation path of successive lithotripter pulses, especially in the acoustic coupling cushion of the shock wave source, they will consume part of the incident wave energy, leading to reduced tensile pressure in the focal region and thus lower stone comminution efficiency. We introduce a method to remove cavitation nuclei from the coupling cushion between successive shock exposures using a jet of degassed water. As a result, pre-focal bubble nuclei lifetime quantified by B-mode ultrasound imaging was reduced from 7 to 0.3 s by a jet with an exit velocity of 62 cm s−1. Stone fragmentation (percent mass <2 mm) after 250 shocks delivered at 1 Hz was enhanced from 22 ± 6% to 33 ± 5% (p = 0.007) in water without interposing tissue mimicking materials. Stone fragmentation after 500 shocks delivered at 2 Hz was increased from 18 ± 6% to 28 ± 8% (p = 0.04) with an interposing tissue phantom of 8 cm thick. These results demonstrate the critical influence of cavitation bubbles in the coupling cushion on stone comminution and suggest a potential strategy to improve the efficacy of contemporary shock wave lithotripters.

Stone comminution correlates with the average peak pressure incident on a stone during shock wave lithotripsy

To investigate the roles of lithotripter shock wave (LSW) parameters and cavitation in stone comminution, a series of in vitro fragmentation experiments have been conducted in water and 1,3-butanediol (a cavitation-suppressive fluid) at a variety of acoustic field positions of an electromagnetic shock wave lithotripter. Using field mapping data and integrated parameters averaged over a circular stone holder area (Rh=7mm), close logarithmic correlations between the average peak pressure (P+(avg)) incident on the stone (D=10mm BegoStone) and comminution efficiency after 500 and 1000 shocks have been identified. Moreover, the correlations have demonstrated distinctive thresholds in P+(avg) (5.3MPa and 7.6MPa for soft and hard stones, respectively), that are required to initiate stone fragmentation independent of surrounding fluid medium and LSW dose. These observations, should they be confirmed using other shock wave lithotripters, may provide an important field parameter (i.e., P+(avg)) to guide appropriate application of SWL in clinics, and facilitate device comparison and design improvements in future lithotripters.

Quantitative Assessment of Shockwave Lithotripsy Accuracy and the Effect of Respiratory Motion

Effective stone comminution during shockwave lithotripsy (SWL) is dependent on precise three-dimensional targeting of the shockwave. Respiratory motion, imprecise targeting or shockwave alignment, and stone movement may compromise treatment efficacy. The purpose of this study was to evaluate the accuracy of shockwave targeting during SWL treatment and the effect of motion from respiration. Ten patients underwent SWL for the treatment of 13 renal stones. Stones were targeted fluoroscopically using a Healthtronics Lithotron (five cases) or Dornier Compact Delta II (five cases) shockwave lithotripter. Shocks were delivered at a rate of 1 to 2 Hz with ramping shockwave energy settings of 14 to 26 kV or level 1 to 5. After the low energy pretreatment and protective pause, a commercial diagnostic ultrasound (US) imaging system was used to record images of the stone during active SWL treatment. Shockwave accuracy, defined as the proportion of shockwaves that resulted in stone motion with shockwave delivery, and respiratory stone motion were determined by two independent observers who reviewed the ultrasonographic videos. Mean age was 51 ± 15 years with 60% men, and mean stone size was 10.5 ± 3.7 mm (range 5-18 mm). A mean of 2675 ± 303 shocks was delivered. Shockwave-induced stone motion was observed with every stone. Accurate targeting of the stone occurred in 60% ± 15% of shockwaves. US imaging during SWL revealed that 40% of shockwaves miss the stone and contribute solely to tissue injury, primarily from movement with respiration. These data support the need for a device to deliver shockwaves only when the stone is in target. US imaging provides real-time assessment of stone targeting and accuracy of shockwave delivery.

2080 ASSESSING THE EFFECTS OF RESPIRATORY MOTION ON STONE COMMINUTION DURING SHOCK WAVE LITHOTRIPSY (SWL) IN AN IN VITRO MODEL

You have accessJournal of UrologyStone Disease: Basic Research I1 Apr 20122080 ASSESSING THE EFFECTS OF RESPIRATORY MOTION ON STONE COMMINUTION DURING SHOCK WAVE LITHOTRIPSY (SWL) IN AN IN VITRO MODEL Muhammad W. Iqbal, Agnes J. Wang, Nathan B. Smith, Gregory T. Baldwin, Gastón M. Astroza, Zachariah G. Goldsmith, F. Hadley Cocks, Michael E. Lipkin, Michael N. Ferrandino, W. Neal Simmons, Glenn M. Preminger, and Pei Zhong Muhammad W. IqbalMuhammad W. Iqbal Durham, NC More articles by this author , Agnes J. WangAgnes J. Wang Durham, NC More articles by this author , Nathan B. SmithNathan B. Smith Durham, NC More articles by this author , Gregory T. BaldwinGregory T. Baldwin Durham, NC More articles by this author , Gastón M. AstrozaGastón M. Astroza Durham, NC More articles by this author , Zachariah G. GoldsmithZachariah G. Goldsmith Durham, NC More articles by this author , F. Hadley CocksF. Hadley Cocks Durham, NC More articles by this author , Michael E. LipkinMichael E. Lipkin Durham, NC More articles by this author , Michael N. FerrandinoMichael N. Ferrandino Durham, NC More articles by this author , W. Neal SimmonsW. Neal Simmons Durham, NC More articles by this author , Glenn M. PremingerGlenn M. Preminger Durham, NC More articles by this author , and Pei ZhongPei Zhong Durham, NC More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2012.02.2246AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES Various methods have been employed to improve stone comminution during SWL. We evaluated the effects of respiratory motion in an in vitro model with an electromagnetic lithotripter, incorporating both an original acoustic focusing lens and a newer lens modified to have a focal size that better resembles that of the Dornier HM3. METHODS Spherical Bego Stone phantoms (44 trials with each lens) 1 cm in diameter were placed in a flat-based cylindrical tube holder attached to a translational stage and set into translational motion with various excursion distances (D), representing kidney displacement, with D = 15mm representing normal respiration and D = 30mm representing deep respiration. Three respiratory rates representative of slow, fast , and very fast breathing were chosen along with various drift factors. The Siemens electromagnetic lithotripter was aligned to focus stone at the superior position representing the kidney position at expiratory pause. Each stone treatment consisted of 2000 shock waves delivered with two different acoustic lenses, the standard and the novel with large focal size resembling that of Dornier HM3 with equivalent energies. RESULTS In 4 of 6 configurations tested with low drift, the new lens statistically improved stone comminution (p<0.01) compared to the original lens design. Comparing single lens results for different respiratory motion patterns, an excursion distance of D = 30 mm resulted in statistically lower comminution (p < 0.01) than D = 15 mm for all cases except for high drift respiration using the new lens. An increase in breathing rate from 12 to 24 Breaths per min resulted in statistically lower comminution for both lenses (p<0.01). CONCLUSIONS Comminution efficiency has a strong dependence on excursion distance, respiratory rate, and stone drift. A new acoustic lens with a wider focal zone provided better stone comminution despite differences in respiratory rate or excursion. Further in vivo studies are needed to determine if these results translate into improved clinical outcomes. © 2012 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 187Issue 4SApril 2012Page: e838 Advertisement Copyright & Permissions© 2012 by American Urological Association Education and Research, Inc.MetricsAuthor Information Muhammad W. Iqbal Durham, NC More articles by this author Agnes J. Wang Durham, NC More articles by this author Nathan B. Smith Durham, NC More articles by this author Gregory T. Baldwin Durham, NC More articles by this author Gastón M. Astroza Durham, NC More articles by this author Zachariah G. Goldsmith Durham, NC More articles by this author F. Hadley Cocks Durham, NC More articles by this author Michael E. Lipkin Durham, NC More articles by this author Michael N. Ferrandino Durham, NC More articles by this author W. Neal Simmons Durham, NC More articles by this author Glenn M. Preminger Durham, NC More articles by this author Pei Zhong Durham, NC More articles by this author Expand All Advertisement Advertisement PDF downloadLoading ...

Reduction of Bubble Cavitation by Modifying the Diffraction Wave from a Lithotripter Aperture

A new method was devised to suppress the bubble cavitation in the lithotripter focal zone to reduce the propensity of shockwave-induced renal injury. An edge extender was designed and fabricated to fit on the outside of the ellipsoidal reflector of an electrohydraulic lithotripter to disturb the generation of diffraction wave at the aperture, but with little effect on the acoustic field inside the reflector. Although the peak negative pressures at the lithotripter focus using the edge extender at 20 kV were similar to that of the original configuration (-11.1 ± 0.9 vs -10.6 ± 0.7 MPa), the duration of the tensile wave was shortened significantly (3.2 ± 0.54 vs 5.83 ± 0.56 μs, P<0.01). There is no difference, however, in both the amplitude and duration of the compressive shockwaves between these two configurations as well as the -6 dB beam width in the focal plane. The significant suppression effect of bubble cavitation was confirmed by the measured bubble collapse time using passive cavitation detection. At the lithotripter focus, while only about 30 shocks were needed to rupture a blood vessel phantom using the original HM-3 reflector at 20 kV, no damage could be produced after 300 shocks using the edge extender. Meanwhile, the original HM-3 lithotripter at 20 kV can achieve a stone comminution efficiency of 50.4 ± 2.0% on plaster-of-Paris stone phantom after 200 shocks, which is comparable to that of using the edge extender (46.8 ± 4.1%, P=0.005). Modifying the diffraction wave at the lithotripter aperture can suppress the shockwave-induced bubble cavitation with significant reduced damage potential on the vessel phantom but satisfactory stone comminution ability.

Synergistic interaction between stress waves and cavitation is important for successful comminution of residual stone fragments in shock wave lithotripsy

To assess the role of stress waves and cavitation in comminuting residual fragments during shock wave lithotripsy (SWL), cylindrical 4 × 4 mm BegoStone phantoms were treated in an electromagnetic lithotripter either at the focus (z = 0, p+ = ∼45 MPa) or pre-focally (z = −30 mm, p+ = ∼24 MPa). The treatment was performed with the stone immersed either in degassed water or in Butanediol, which has similar acoustic impedance to water but much higher viscosity to suppress cavitation. At the focus, the first fracture was observed after 26 ± 9 shocks, both in water and Butanediol (p = 0.7). However, when stones were moved pre-focally where comparable cavitation is produced (based on high speed imaging), the average shock number required for the initial fracture was increased to 66 ± 10 in water and 122 ± 20 in Butanediol (p = 0.002). Below −40 mm prefocally (p+ < 20 MPa), stones did not fracture in water even after 2,000 shocks, although cavitation was observed. Furthermore, stone comminution at the focus after 250 shocks was ∼35% in water compared to ∼5% in Butanediol (p < 0.001). Altogether, these findings suggest that a synergistic interaction between stress waves and cavitation is critical in producing effective stone comminution during SWL. [Work supported by NIH and NSF GRFP.]

In vitro comminution of model renal calculi using histotripsy

Shock wave lithotripsy (SWL) suffers from the fact that it can produce residual stone fragments of significant size (>2 mm). Mechanistically, cavitation has been shown to play an important role in the reduction of such fragments to smaller debris. In this study, we assessed the feasibility of using cavitationally-based pulsed ultrasound therapy (histotripsy) to erode kidney stones. Previous work has shown that histotripsy is capable of mechanically fractionating soft tissue into fine, acellular debris. Here, we investigated the potential for translating this technology to renal calculi through the use of a commonly accepted stone model. Stone models were sonicated using a 1-MHz focused transducer, with 5-cycle pulses delivered at a rate of 1 kHz. Pulses having peak negative pressures ranging from 3 to 21 MPa were tested. Results indicate that histotripsy is capable of effectively eroding the stone model, achieving an average stone erosion rate of 26 mg/min at maximum treatment pressure; substantial stone erosion was only observed in the presence of a dense cavitational bubble cloud. Sequential sieving of residual stone fragments indicated that debris produced by histotripsy was smaller than 100 μm in size, and treatment monitoring showed that both the cavitational bubble cloud and model stone appear as hyperechoic regions on B-mode imaging. These preliminary results indicate that histotripsy shows promise in its use for stone comminution, and an optimized erosion process may provide a potential adjunct to conventional SWL procedures.

Assessing the effects of respiratory motion on stone comminution in vitro.

The effects of respiratory motion on stone comminution produced by an electromagnetic (EM) shock wave lithotripter were evaluated in vitro. Individual spherical BegoStone phantoms (D = 10 mm) were placed in a flat‐base tube holder and treated at various radial distances in the lithotripter focal plane. To assess the effects of respiratory motion on stone comminution, the holder was set into translational motions in another series of experiments with various excursion distances (1.5–3.0 cm), breath rates (12–24 bpm), and drift factors for motion randomization. Stone comminution tests were performed using either a newly designed acoustic lens with a wide focal width and a low peak pressure or the original lens under equivalent acoustic energies. The results shows that the new lens produces statistically higher stone comminution (p < 0.01) than the original lens. Moreover, stone comminution at various radial distances will be compared, together with cavitation potential calculated by the Gilmore model based ...