Extracorporeal Shock Wave Lithotripter Research Articles

Evaluation of efficiency of two extracorporeal shockwave lithotripters – Medilit 7 and Sonolith i-sys in comparison with ureterorenoscopy

Evaluation of efficiency of two extracorporeal shockwave lithotripters – Medilit 7 and Sonolith i-sys in comparison with ureterorenoscopy

Single Center, Single Operator Comparative Study of the Efficacy and Outcomes of Electrohydraulic and Electromagnetic Extracorporeal Shock Wave Lithotriptors

Single Center, Single Operator Comparative Study of the Efficacy and Outcomes of Electrohydraulic and Electromagnetic Extracorporeal Shock Wave Lithotriptors

E8 Efficacy of mobile extracorporeal shock wave lithotripter in lower pole renal stones treatment

E8 Efficacy of mobile extracorporeal shock wave lithotripter in lower pole renal stones treatment

Underwater Shock Wave Research Applied to Therapeutic Device Developments

The chronological development of underwater shock wave research performed at the Shock Wave Research Center of the Institute of Fluid Science at the Tohoku University is presented. Firstly, the generation of planar underwater shock waves in shock tubes and their visualization by using the conventional shadowgraph and schlieren methods are described. Secondly, the generation of spherical underwater shock waves by exploding lead azide pellets weighing from several tens of micrograms to 100 mg, that were ignited by irradiating with a Q-switched laser beam, and their visualization by using double exposure holographic interferometry are presented. The initiation, propagation, refl ection, focusing of underwater shock waves, and their interaction with various interfaces, in particular, with air bubbles, are visualized quantitatively. Based on such a fundamental underwater shock wave research, collaboration with the School of Medicine at the Tohoku University was started for developing a shock wave assisted therapeutic device, which was named an extracorporeal shock wave lithotripter (ESWL). Miniature shock waves created by irradiation with Q-switched HO:YAG laser beams are studied, as applied to damaged dysfunctional nerve cells in the myocardium in a precisely controlled manner, and are effectively used to design a catheter for treating arrhythmia.

Design of the Dual Stone Locating System on an Extracorporeal Shock Wave Lithotriptor

Extracorporeal Shock Wave Lithotriptors are very popular for the treatment of urinary stones all over the world. They depend basically upon either X-ray fluoroscopy or ultrasound scans to detect the stones before therapy begins. To increase the effectiveness of treatment this study took advantage of both X-ray and ultrasound to develop a dual stone locating system with image processing modules. Its functions include the initial stone locating mode with stone detection by fluorescent images and the follow-up automatic stone tracking mode made by constant ultrasound scanning. The authors have integrated both apparatus and present the operating principles for both modes. The system used two in vitro experiments to justify its abilities of stone location in all procedures.

Time-Resolved High-Speed Visualization and Analysis of Underwater Shock Wave Focusing Generated by a Magnetic Pulse Compression Unit

Paper reports on visualization and analysis of underwater shock waves generation, focusing, and propagation. Recently, shock waves have been attractive with rising attention in medical field. Extracorporeal shock wave lithotripter has been one of its very successful applications. However, the effects of shock waves on living tissue are not sufficiently understood, due to unknown parameters involving the shock wave interaction. For better understanding of affecting points, a precise and controllable shock wave source is required. In this paper, in order to study shock wave effects, pulsed electric discharges produced by magnetic pulse compression circuit were used to generate underwater shock waves. A half-ellipsoidal reflector was used for shock wave focusing. The whole sequences of the shock wave generation, propagation, focusing, and cavitation bubbles, which appeared after shock wave passage, were visualized by time-resolved high-speed shadowgraph method. The peak pressure of shock wave focusing at second focal point reached 180 MPa. A cylindrical test section was used to observe phenomena around the electrode from the pulse discharge to bubble collapse. The first cavitation bubble's collapse occurred at about 750 μs. In the experiment, the two shock waves, one generated by expansion of plasma and another generated by collapse of the cavitation bubble were studied. Using high-speed visualization and image analysis, the velocity and pressure of the two shock waves were evaluated. The peak pressure of shock wave generated by bubble collapse reached 157 MPa.

Evaluation of resource allocation and supply-demand balance in clinical practice with high-cost technologies

Japan has one of the highest numbers of high-cost medical devices installed relative to its population. While evaluations of the distribution of these devices traditionally involve simple population-based assessments, an indicator that includes the demand of these devices would more accurately reflect the situation. The purpose of this study was to develop an indicator of the supply-demand balance of such devices, using examples of magnetic resonance imaging scanners (MRI) and extracorporeal shockwave lithotripters (ESWL), and to investigate the relationship between this indicator, personnel distribution statuses and operating statuses at the prefectural level. Using data from nation-wide surveys and claims data from 16 hospitals, we developed an indicator based on the ratio of the supplied number of device units to the number of device units in demand for MRI and ESWL. The latter value was based on patient volume and utilization proportion. Correlation analyses were conducted between the supply-demand balances of these devices, personal distribution and operating statuses. Comparisons between our indicator and conventional population-based indicators revealed that 15% and 30% of prefectures were at risk of underestimating the availability of MRI and ESWL, respectively. The numbers of specialist personnel/device units showed significant, negative correlations with our indicators in both devices. Utilization-based analyses of health care resource placement and utilization status provide a more accurate indication than simple population-based assessments, and can assist decision makers in reviewing gaps between health policy and management. Such an indicator therefore has the potential to be a tool in helping to improve the efficiency of the allocation and placement of such devices.

Effect of Escalating Versus Fixed Voltage Treatment on Stone Comminution and Renal Injury During Extracorporeal Shock Wave Lithotripsy: A Prospective Randomized Trial

ESWL is a minimally invasive, efficacious therapy for most renal stones. However, an optimal voltage treatment protocol ensuring effective stone comminution while minimizing tissue injury is not well established. We performed a prospective, randomized trial of the stone-free rate and renoprotective effect of an escalating vs a fixed voltage treatment strategy during ESWL. Between February 2006 and June 2008 we enrolled 45 patients undergoing ESWL for a renal stone in this institutional review board approved trial. A Dornier DoLi 50 lithotriptor was used. Patients were randomized to receive the escalating strategy of 500 shocks at 14k V, 1,000 at 16 kV and 1,000 at 18 kV or the fixed strategy of 2,500 shocks at 18 kV. Abdominal x-ray was done to determine the stone-free rate at 1 month. Voided urine was analyzed for beta2-microglobulin and microalbumin before, immediately after and 1 week after ESWL to evaluate renal damage. Median patient age was 48 years. Median stone size was 8 mm. Of patients in the escalating group 81% were stone-free vs 48% in the fixed group (p <0.03). There was a significant difference between microalbumin and beta2-microglobulin 1 week after the procedure (p = 0.046 vs 0.045). There was trend toward a difference in microalbumin and beta2-microglobulin immediately after the procedure (p = 0.17 and 0.25, respectively). This prospective, randomized study shows that an escalating voltage treatment strategy produces better stone comminution than a fixed strategy. The study suggests that there may be a protective effect against damage caused by ESWL with an escalating treatment strategy.

LithoGold: A Novel Third Generation Extracorporeal Shock Wave Lithotriptor for the Management of Pancreatic Duct Stones in Symptomatic Chronic Calcific Pancreatitis

Purpose: Extracorporeal shock wave lithotripsy (ESWL) is an important tool for non-operative management of symptomatic pancreatic duct (PD) stones. Fragmentation of stones may permit endoscopic extraction at ERP thereby avoiding surgical intervention. First generation devices used water immersion and fluoroscopic targeting and became an integral adjunct in the non-operative management of painful chronic pancreatitis (CP). Second generation devices had self-contained water conducters and lower power profiles with ultrasound targeting but were ineffective for PD stones. LithoGold (Woodstock, GA) represents the third generation of ESWL with fluoroscopic targeting and a similar power profile to first generation devices. We aim to determine the safety and efficacy of this latest generation ESWL device on stone fragmentation and endoscopic management of painful CP. Methods: Retrospective chart review of all patients (pts) undergoing either first generation ESWL (fESWL) vs. LithoGold (LG) from 6/02 to 10/08 at UPMC. Outcomes included successful completion of ESWL, complications, clearance of the main PD at subsequent ERPs, improvement in symptoms, and number of pts ultimately requiring surgery. Results: 17 pts (8 fESWL, 9 LG) underwent therapy for symptomatic PD stones (mean age 54 years [range 40-76]; 11 males, 6 females). All pts underwent ERP prior to ESWL with placement of PD stent in 12/17. 8/8 successfully completed fESWL with mean of 1.9 treatments/pt (range 1-4) compared to 8/9 successfully completing LG with mean of 1.1 treatments/pt (range 1-2). A single failure occurred in the LG group due to interference of the spinal vertebrae with the shock wave despite oblique positioning of the pt. On average, 1150 shocks (range 800-2000) at 20 kV were administered with fESWL and 1670 shocks (range 1000-2750) at 24kV with LG. There were no complications in the fESWL group and only one case of transient hematuria in the LG group. Clearance of the PD at subsequent ERPs was reported in 7/8 (88%) pts with fESWL and 6/8 (75%) pts with LG. Initially, 7/8 (88%) pts in fESWL group and 6/8 (75%) pts in LG group reported symptom improvement after stone extraction. Ultimately, 3/8 (38%) in the fESWL group and 1/8 (13%) in the LG group required surgery. Conclusion: In our experience, LG is safe and effective with comparable results to fESWL for the treatment of symptomatic PD stones. The portability of the LG unit obviates the need for a specialized unit equipped with a water basin for fESWL. The disparity in surgical intervention may be attributed to longer follow-up in the fESWL group. Randomized studies are needed to determine the efficacy of third generation lithotriptors for treating PD stones.

Novel Electromagnetic Lithotriptor for Upper Tract Stones With and Without a Ureteral Stent

We compared the treatment efficacy and safety of the novel Lithoskop electromagnetic extracorporeal shock wave lithotriptor for upper urinary tract stones with and without prior ureteral stent placement. A total of 665 consecutive patients harboring single renal or ureteral stones underwent shock wave lithotripsy between August 2006 and July 2008. In 75 and 46 patients with renal and ureteral stones, respectively, stents were placed before the first shock wave lithotripsy session. Treatment outcome was assessed in relation to stent placement. All data were derived from a prospectively maintained database. The mean size of nonstented vs stented renal and ureteral stones was 8.6 vs 12.5 mm (p <0.0001) and 7.1 vs 7.3 mm (p = 0.6), respectively. The stone-free rate in nonstented vs stented renal and ureteral stone cases was 76.3% vs 77.3% and 91.4% vs 93.5%, respectively (each p >0.99). The total energy applied per stone was 110 +/- 83 vs 150 +/- 89 J (p <0.0001) and 183 +/- 131 vs 209 +/- 125 J (p = 0.1), respectively. Auxiliary measures were required after shock wave lithotripsy for renal and ureteral stones in 5.4% and 10.8% of nonstented, and in 1.3% and 4.3% of stented cases, respectively. No complications were detected in stented renal and ureteral stone cases compared to 2.9% and 6.9% in nonstented cases, respectively. A high success rate and a low complication rate were achieved in renal and ureteral stone cases with and without prior ureteral stent placement. Total energy needed to achieve a stone-free state did not differ between stented and nonstented ureteral cases, suggesting the absence of a significant influence of the stent. Overall stents decreased complications necessitating hospitalization and auxiliary invasive measures.

Pediatric Ureteroscopic Management of Intrarenal Calculi

Data addressing ureteroscopic management of intrarenal calculi in prepubertal children are limited. We reviewed our experience from January 2002 through December 2007. We retrospectively reviewed ureteroscopic procedures for intrarenal calculi in children younger than 14 years. Stone-free status was determined with postoperative imaging. Multiple logistic regression analysis was used to assess the influence of preoperative factors on initial stone-free status and the need for additional procedures. Intrarenal calculi were managed ureteroscopically in 52 kidneys in 50 children with a mean age of 7.9 years (range 1.2 to 13.6). Mean stone size was 8 mm (range 1 to 16). Stone-free rate after a single ureteroscopic procedure was 50% (25 of 50 patients) on initial postoperative imaging and 58% (29 of 50) with extended followup. Initial stone-free status was dependent on preoperative stone size (p = 0.005) but not stone location. Additional stone procedures were required in 18 upper tracts. Younger patient age (p = 0.04) and larger preoperative stone size (p = 0.002) were associated with the need for additional procedures. Additional procedures were required in more than half of the stones 6 mm or larger but in no stone smaller than 6 mm. Ureteroscopy is a safe method for the treatment of intrarenal calculi in the prepubertal population. Our ureteroscopic stone-free rate for intrarenal stones is lower than that reported for ureteral stones. Parents should be informed that additional procedures will likely be required, especially in younger patients and those with stones larger than 6 mm.

The Trend Change of Incidence and Treatment of Urolithiasis between the 1980s and 2000s

Purpose: The incidence of urolithiasis has recently shown an increasing tendency in relation to improvements in living conditions in Korea. With the development of extracorporeal shock wave lithotriptor (ESWL), endourology and other new instruments, urolithiasis has become easier to treat, without surgical intervention. The incidence and treatment of urolithiasis, between the 1980 and 2000, were evaluated. Materials and Methods: 328 and 1,142 patients with urolithiasis, either admitted between January 1981 and December 1984 or treated at the out-patient clinic between January 2001 and December 2004, respectively, were analyzed. Results: In the early 1980s, 328 (27.3%) patients of the total 1,203 admitted to the urology department had urolithiasis. In the early 2000s, 1,142 patients were treated for urolithiasis. The total number and incidence constantly increased over the stated period. The ratio of males to females was 1.3:1 in the 1980s and 2.0:1 in the 2000s. The occurrence rate for those under 20 years decreased, but increased after the 6th decade. And the seasonal occurrence was highest during the summer of the early 1980s, but there was no seasonal difference during the early 2000s. The incidences of lower ureteral, bladder and urethral calculi were decreased, but those of renal and upper ureteral calculi increased. In the management of urolithiasis, open surgery and expectant therapy decreased during the 2000s. In the endourological management of urolithiasis, the success rates of ESWL, percutaneous nephrolithotomy (PNL) and ureteroscopic removal of stone (URS) were 94.5, 86.6 and 96.4%, respectively. Conclusions: The incidence and treatment modalities of urolithiasis have changed, especially since the late 1980s. (Korean J Urol 2007;48:40-44) ꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏ

Comparative Results of Extracorporeal Shock Wave Lithotripters with Three Kinds of Shock Wave Generator

was lower in group C than in groups A and B. According to the location, group C had a lower success rate than groups A and B for renal stones, while there were no differences between the three groups in the treatment of other stone locations. The number of treatment sessions for group A was greater than those for groups B and C (group A, 3.83; group B, 1.85; group C, 1.93). Many more sessions were required for group A in comparison with groups B and C in case of renal stones, ureteropelvic junction and upper ureteral stones. The number of sessions for group B was the least for lower ureteral stones. Complications, including stein- strasse, fever, perirenal hematoma and hematuria, were detected in groups A, B and group C at 10, 15.3 and 7.1%, respectively. Conclusions: There were no differences in the success rates between the three extracorporeal shock wave lithotripters using a shock wave gener- ator. The mean number of treatment sessions was most with the pie- zoelectric type; whereas, complications were most prevalent with the electromagnetic type. (Korean J Urol 2007;48:54-60) ꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏ

INNOVATIONS IN SHOCK WAVE LITHOTRIPSY TECHNOLOGY: UPDATES IN EXPERIMENTAL STUDIES

We developed innovations in shock wave lithotripsy (SWL) technology. Two technical upgrades were implemented in an original unmodified HM-3 lithotriptor (Dornier Medical Systems, Inc., Kennesaw, Georgia). First, a single unit ellipsoidal reflector insert was used to modify the profile of lithotriptor shock wave (LSW) to decrease the propensity of tissue injury in SWL. Second, a piezoelectric annular array (PEAA) generator (f = 230 kHz and F = 150 mm) was used to produce an auxiliary shock wave of approximately 13 MPa in peak pressure (at 4 kV output voltage) to intensify the collapse of LSW induced bubbles near the target stone for improved comminution efficiency. Consistent rupture of a vessel phantom made of single cellulose hollow fiber (i.d. = 0.2 mm) was produced after 30 shocks by the original HM-3 reflector at 20 kV. In comparison no vessel rupture could be produced after 200 shocks using the upgraded reflector at 22 kV or the PEAA generator at 4 kV. Using cylindrical BegoStone phantoms (Bego USA, Smithfield, Rhode Island) stone comminution efficiencies (mean +/- sd) after 1,500 shocks produced by the original and upgraded HM-3 reflectors, and the combined PEAA/upgraded HM-3 system, were 81.3% +/- 3.5%, 90.1% +/- 4.3% and 95.2% +/- 3.3%, respectively (p<0.05). Optimization of the pulse profile and sequence of LSW can significantly improve stone comminution while simultaneously decreasing the propensity of tissue injury during in vitro SWL. This novel concept and associated technologies may be used to upgrade other existing lithotriptors and to design new shock wave lithotriptors for improved performance and safety.

Development of a system of automatic gap-adjusted electrodes for shock wave generators

In this study, a system of automatic gap-adjusted electrodes is developed for electrohydraulic shock wave generators that can be used both for extracorporeal shock wave lithotripsy (treatment of renal calculi) and for the extracorporeal shock wave therapy for musculo-skeletal disorders. This system is composed of three main components: (1) two electrodes and their bases; (2) servo motors and control software; (3) a high sensitivity CCD camera and image processing program. To verify system performance, in vitro fragmentation tests have been conducted using kidney stone phantoms. Results indicate that the efficiency of stone fragmentation using automatic gap adjustment can be increased up to 55.2%, which is twice more than without automatic gap adjustment (26.7%). This system can be applied to any commercial electrohydraulic extracorporeal shock wave lithotriptor or orthotriptor without difficulty.

Stone fragmentation by ultrasound

The presence of kidney stone in the kidney causes discomfort to patients. Hence, removal of such stones is important which is commonly done these days, non-destructively, with lithotripters without surgery. Commercially, lithotripters like extra-corporeal shock wave lithotripters (ESWL) made by Siemens etc are in routine use. These methods are very cumbersome and expensive. Treatment of the patients also takes comparatively more time because of more number of sittings. Some delicate nerves and fibres in the surrounding areas of the stones present in the kidney are also damaged by high ultrasonic intensity used in such systems. In the present work, enhancement of the kidney stone fragmentation by using ultrasound is studied. The cavitation bubbles are found to implode faster, with more disintegration efficiency of the lithotripters, which give better treatment to the patients.

Extracorporeal Shock Wave Lithotripsy (ESWL) and Endoscopic Management of Intrahepatic Lithiasis

Background and aims: Intrahepatic lithiasis (IHL) is prevalent in East Asia, but relatively uncommon in Western societies. Bile stasis or biliary infections can lead to stone formation; strictures or dilations are often encountered in association with IHL. Treatment can be difficult and includes a surgical, percutaneous or endoscopic approach. The main objective of treatment is the complete removal of stones. The aim of this study is to assess the role of Electromagnetically generated extracorporeal shock waves lithotripsy (ESWL) associated with the endoscopic retrograde treatment of intrahepatic lithiasis. Patients and Methods: From November 1987 to April 2002, 215 patients (122 male, mean age 57.3, range 19-91) with intrahepatic lithiasis underwent endoscopic retrograde colangiography and stone extraction. A second generation extracorporeal shock wave lithotriptor (Siemens-Lithostar Plus: Erlangen, Germany) has been used since 1994 to achieve fragmentation of stones that could not be cleared during ERCP. Premedication of patients for ESWL treatment included sedation with diazepam (5-10 mg i.v.), morphine (5-10 mg i.v.), Ketoprofene (50-100 mg i.v.). All procedures were performed under fluoroscopy after insertion of a naso-biliary drainage. Patients were divided retrospectively in 2 groups: patients treated before 1994 (Group 1) and after 1994 (Group 2). Case-control analysis was performed between the 2 groups comparing ESWL rate and stone extraction success rate and for the evaluation of patients with congenital and post-operative strictures. Results: see the table. Conclusions: ESWL is a useful technique in the treatment of IHL. Associated to ERCP it significantly increases the complete stone extraction success rate. It seems to be effective also in patients with congenital or post-operative strictures even if the small group does not produce a statistically significant difference.

Evaluation of Synchronous Twin Pulse Technique for Shock Wave Lithotripsy: Determination of Optimal Parameters for In Vitro Stone Fragmentation

The Twinheads extracorporeal shock wave lithotriptor (THSWL) is composed of 2 identical shock wave generators and reflectors. One reflector is under the table and the other is over the table with a variable angle between the axes of the 2 reflectors. The 2 reflectors share a common second focal point, making it possible to deliver an almost synchronous twin pulse to the targeted stone. We studied the optimal parameters for in vitro stone fragmentation. Two types of 1 cm artificial stones were used, namely Bon(n)-stones of 3 compositions (75% calcium oxalate monohydrate [COM] plus 25% uric acid, struvite and cystine) and plaster of Paris. The parameters tested were shock wave number (100, 500 and 1,000), shock wave power (8, 11 and 14 kV) and angle between the reflector axes (67, 90 and 105 degrees). After the optimal parameters were determined we studied the disintegrative efficacy of THSWL for 3 types of human urinary calculi, including COM, calcium hydrogen phosphate (brushite) and cystine. Each stone received 1,000 twin shock waves at 14 kV with an angle of 90 degrees between the reflectors. All experiments were done using a rate of 60 twin shock waves per minute. Following lithotripsy stone fragments were processed and sized. The ratio of the weight of fragments greater than 2 mm-to-total weight of all fragments was calculated. Optimal stone fragmentation results for THSWL were obtained with the maximum number of shock waves (1,000) and full power (14 kV). There was no significant statistical difference in fragment size or the ratio of fragments greater than 2 mm with the use of different angles except for cystine and plaster of Paris calculi, for which the right angle was most effective. At application of the optimal parameters to human stones THSWL produced small fragment size for COM and cystine stones, while brushite stones were not fragmented to the same extent. The efficacy of synchronous twin pulse technology improves as the number of shock waves and power increase. A 90-degree angle between the shock wave reflectors is advantageous for certain stones (that is cystine and plaster of Paris) but it is not a factor for other stone compositions. THSWL has satisfactory disintegrative efficacy for human stones, especially COM and cysteine calculi.

Prospective Randomized Comparative Study of the Effectiveness and Safety of Electrohydraulic and Electromagnetic Extracorporeal Shock Wave Lithotriptors

We compared the efficacy of 2 shock wave energy sources, electrohydraulic (Dornier MFL 5000, Dornier MedTech, Wessling, Germany) and electromagnetic (DLS, Dornier Lithotriptor S, Dornier MedTech), for the treatment of urinary calculi. A prospective randomized study of 694 patients with urinary stones was conducted during 12 months to compare the efficacy of the 2 machines. Entrance criteria were radiopaque single or multiple stones at any location within the kidney or the ureter, 25 mm or smaller that had not previously been treated by any means. Patients with congenital anomalies were excluded from this study with all other contraindications for extracorporeal shock wave lithotripsy. Following lithotripsy a plain abdominal film and tomograms were done 1 week after each session to determine if there were residual stones and assess the need for re-treatment. Patients were evaluated 4 weeks after lithotripsy by plane abdominal x-ray and spiral computerized tomography. Success was defined as no residual stones. Univariate and multivariate statistical analyses were performed for different variables that may have an impact on the success rate, including the type of lithotriptor. Comparisons of treatment parameters, complications and success rate for both lithotriptors were done. Of 9 variables examined with univariate analysis 6 had a significant impact on the success rate. Of these 4 maintained their statistical impact on multivariate analysis. These were side, site of the stones, renal morphology and type of lithotriptor. Treatment time was significantly shortened for DLS (54 +/- 32.9 minutes compared to 65.7 +/- 44.7 for MFL, p <0.001). The re-treatment rate was lower for DLS at 34% versus 51.6% for the MFL (p <0.001). The overall success rate was 85.4%. It was 88.5% for DLS compared to 82.4% for MFL (p = 0.03). No statistically significant difference between the lithotriptors was noted for ureteral calculi (p >0.05). The success rate was higher in the DLS group for renal stones especially lower caliceal and pyelic stones (p <0.05). The success rate was higher in DLS group for stones 10 mm or smaller, 92.8% versus 85.3% for MFL (p = 0.03). The success rate was comparable in both groups for stones larger than 10 mm (81.8% for DLS versus 77.9% for MFL, p >0.05). No statistically significant difference was found in the complication rate for the groups. Steinstrasse were noted in 4% of patients treated with MFL and 3% of those treated with DLS. Subcapsular hematomas were noted in 2 patients in each group. No procedures after extracorporeal shock wave lithotripsy were needed in either group. The electromagnetic lithotriptor (Dornier lithotriptor S) has significant clinical advantages over the electrohydraulic lithotriptor (Dornier MFL 5000) in terms of treatment time, re-treatment rate and success rate, although there is no difference in the complication rate.

Cavitation inception following shock wave passage

Cavitation bubble nucleation following the passage of an extracorporeal shock wave lithotripter pulse is investigated experimentally and numerically. In the experiments two configurations are considered: Free passage of the shock wave, and reflection of the shock wave from a rigid reflector. The nucleation and the early growth phase of the bubbles including radial and translatory motion is compared with a commonly used model for bubble dynamics, the Gilmore model, which is coupled to a one-dimensional model for translatory motion. Reasonable agreement is found for the predicted translatory motion of the bubble center; however, considerable disagreement between a simple cavitation inception theory and the experiment exists: Cavitation bubbles expand later than predicted pointing to a more complex inception scenario than a single stabilized gas pocket. A hypothesis is proposed to explain the delayed growth of the bubbles. Additional findings are the formation of bands with diminished bubble activity, which very much resemble the structure found by Sokolov et al. (2001). High-speed photographs suggest that bubble–bubble interaction plays an important role in the formation of structured bands.