Enhanced kidney stone fragmentation by short delay tandem conventional and modified lithotriptor shock waves: a numerical analysis

PURPOSE: We evaluated the effectiveness of modified lithotriptor shock waves using computer models. MATERIALS AND METHODS: Finite element models were used to simulate the propagation of lithotriptor shock waves in human renal calculi in vivo. Kidney stones were assumed to be spherical, homogeneous, isotropic and linearly elastic, and immersed in a continuum fluid. Single and tandem shock wave pulses modified to intensify the collapse of cavitation bubbles near the stone surface to increase fragmentation efficiency and suppress the expansion of intraluminal bubbles for decreased vascular injury were analyzed. The effectiveness of the modified shock waves was assessed by comparing the states of loading in the renal calculi induced by these shock waves to those produced by conventional shock waves. RESULTS: Our numerical simulations revealed that modified shock waves produced marginally lower stresses in spherical renal calculi than those produced by conventional shock waves. Tandem pulses of conventional or modified shock waves produced peak stresses in the front and back halves of the renal calculi. However, the single shock wave pulses generated significant peak stresses in only the back halves of the renal calculi. CONCLUSIONS: Our numerical simulations suggest that for direct stress wave induced fragmentation modified shock waves should be as effective as conventional shock waves for fragmenting kidney stones. Also, with a small interval of 20 microseconds between the pulses tandem pulse lithotripsy using modified or conventional shock waves could be considerably more effective than single pulse lithotripsy for fragmenting kidney stones.     

Experience with the Dornier HM4 and MPL 9000 lithotriptors in urinary stone treatment

From November 17, 1987 until August 20, 1988 we operated a fluoroscopy guided Dornier HM4 kidney lithotriptor. This lithotriptor subsequently was replaced by the ultrasound guided Dornier MPL 9000 lithotriptor, a multipurpose machine for urinary and biliary stone treatment. With the Dornier HM4 device we performed 447 treatment sessions in 319 patients (483 stones). The mean number of shock waves was 1,848 per patient. The re-treatment rate was 1.17 per patient. After 3 months 85% of the patients were free of stone. Auxiliary procedures were performed in 27.6% of the sessions. From September 20, 1988 until August 30, 1989 we used the Dornier MPL 9000 lithotriptor on 246 patients with 407 stones in 354 treatment sessions. The mean number of shock waves per session was 1,654 per patient, 1.11 treatments were performed per patient and the rate free of stones after 3 months was 85%. Auxiliary measures before and after lithotripsy were performed in 33.6% of the sessions. The experience with both of these machines is discussed in regard to performance, as well as the specific advantages and disadvantages of the different imaging systems.     

In vitro study of ultrasound based real-time tracking for renal stones in shock wave lithotripsy: Part II--a simulated animal experiment

PURPOSE: We have previously developed and reported an ultrasound based real-time tracking system for renal stones. In the current study we continued to verify the reliability of this tracking system by a simulated animal test. MATERIALS AND METHODS: We used 13 prerecorded ultrasound stone trajectories to test the system. The real-time tracking system was implemented on the Litemed 9200 electrohydraulic lithotriptor (LiteMed Co., Taipei, Taiwan). An artificial stone and tap water were sealed in a balloon. The balloon was inserted into the pelvis of a pig kidney. While the kidney was affixed to and moved by a simulator, it was immersed in a specifically designed simulated animal model tank containing tap water. The stone was localized by ultrasound. The kidney was moved by the simulator according to a prerecorded stone trajectory. A total of 3,000 shock waves were delivered to the stone. For each recorded stone trajectory experiments were done under nontracking and tracking conditions. We performed tests of the fragment-to-weight ratio, which denotes the performance of a shock wave lithotriptor when fragmenting a stone. RESULTS: The mean fragment-to-weight ratio was 55.3% +/- 25.9% in the nontracking and 100% +/- 0% in the tracking group. The difference in these 2 groups was statistically significant (paired t test p <0.01). CONCLUSIONS: The ultrasound based real-time tracking system proved to improve the performance of a shock wave lithotriptor significantly when fragmenting stones in a simulated animal test. We believe that the tracking system would greatly reduce the number of shocks and time needed for treating renal stones.     

Stone fragmentation during shock wave lithotripsy is improved by slowing the shock wave rate: studies with a new animal model

PURPOSE: The current trend toward ungated shock wave lithotripsy means that more patients are being treated with shock waves delivered at a rapid rate (120 shock waves per minute or greater). However, no benefit of an increased shock wave rate has been shown and in vitro studies indicate that slowing the shock wave rate actually improves stone fragmentation. We tested the effect of the shock wave rate on stone comminution in a new animal model. MATERIALS AND METHODS: Gypsum model stones were inserted via upper pole percutaneous access into the lower pole calix of the kidneys of female pigs weighing approximately 100 pounds. Shock wave lithotripsy was performed (400 shock waves uninterrupted at 20 kV. and 30 or 120 shock waves per minute) 2 hours later using an unmodified HM3 lithotriptor (Dornier Medical Systems, Marietta, Georgia). After en bloc excision of the urinary tract stone fragments were collected and sieved through 2 mm. mesh. The particles were weighed and surface area was determined. RESULTS: Stones treated at 30 shock waves per minute broke more completely than stones treated at 120 shock waves per minute. The percent of fragments greater than 2 mm. was significantly higher for stones treated at the fast rate of 120 versus the slow rate of 30 shock waves per minute (mean +/- SEM 81% +/- 14% versus 45% +/- 12%, p <0.005). When stone fragmentation was expressed as the percent increase in fragment surface area, significantly greater fragmentation occurred at the slower than at the more rapid rate (327% +/- 63% versus 135% +/- 136%, p <0.02). CONCLUSIONS: Slowing the rate of shock wave administration during shock wave lithotripsy significantly improves the efficiency of stone fragmentation in vivo.     

CONTROLLED, FORCED COLLAPSE OF CAVITATION BUBBLES FOR IMPROVED STONE FRAGMENTATION DURING SHOCK WAVE LITHOTRIPSY

The feasibility of using controlled, forced collapse of cavitation bubbles for improved stone fragmentation during shock wave lithotripsy was demonstrated using microsecond tandem shockwave pulses. High-speed photography revealed that a secondary shock wave, released in less than 500 microseconds (micro sec.) following a lithotripter-generated shock wave, can be used to control and force the collapse of cavitation bubbles toward target concretions. This timely enforced shockwave-bubble interaction was found to greatly enhance the cavitational activity near the stone surface, with a resultant up to 43% increment in stone fragmentation. Since most of the cavitation energy is directed and concentrated toward the target stones and fewer shock waves are needed for successful stone comminution, tissue injury associated with this new lithotripsy procedure may also be reduced. This novel concept of shock wave lithotripsy may be used to improve the treatment efficiency and safely of existing clinical lithotripters, as well as in the design of new shock wave lithotripters.     

Extracorporeal shock wave lithotripsy in the prone position: treatment of stones in the distal ureter or anomalous kidney

A total of 15 patients underwent ESWL using the Dornier HM3 lithotriptor with the patient in the prone position. The stones were in the distal ureter over the sacroiliac joint in 10 patients, 8 of whom had undergone unsuccessful ureteroscopic manipulation. Two patients had horseshoe kidneys with stones that were too anterior to permit accurate targeting with the patient in the standard supine position. One patient had a solitary stone in a pelvic kidney and 1 had an obstructing ureteropelvic junction stone in a crossed ectopic kidney. The final patient had a reconstructed lower urinary tract with a stone at 1 of the ureterointestinal anastomoses. Excellent pulverization was achieved in all patients after only 1 prone ESWL treatment. One patient required temporary percutaneous nephrostomy after ESWL and 1 may require retrograde manipulation of fragments at the ureterovesical junction. No patient had melena, and other than temporary ileus in 1 patient who had concurrent supine ESWL of renal calculi, no gastrointestinal complications were seen. All but 1 patient were free of stones 1 month after prone ESWL. Prone ESWL prevents blockage of shock wave energy by the bony pelvis, because the shock waves enter anteriorly and exit posteriorly. ESWL with the patient in the prone position is a safe and effective treatment of calculi in the distal ureter or anomalous kidney.     

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

PurposeThe 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.Materials and MethodsTwo 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.ResultsOptimal 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.ConclusionsThe 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.     

Ultrasound stone localisation for extracorporeal shock wave lithotripsy

An extracorporeal shock wave lithotriptor using an ultrasound scan head pantograph location system has been designed. The shock wave ellipsoid reflector position is adjusted to the stone with a computer assisted positioning device. Seven dogs with stones implanted into the renal pelvis were treated and stone fragmentation occurred in all cases. Subsequently, 45 patients with stones were treated. The stones ranged in size from 5 to 29 mm (mean 16). Radio-opaque as well as poorly opaque or radiolucent stones were treated and fragmentation was achieved in 85% of cases. An additional endoscopic procedure was performed in four cases. No fragmentation occurred in four patients. Further shock wave treatment was necessary in two patients who presented with stones larger than 2 cm. Both radio-opaque and poorly opaque stones can be treated with this system. Ultrasound localisation and the ellipsoid positioning device avoid the need for expensive fluoroscopic equipment and a hydraulic patient positioning system.     

Clinical application of Sonolith 2000 type B on extracorporeal shock wave lithotripsy for upper urinary tract calculi

This report describes the results of clinical trials of the second generation extracorporeal shock wave lithotriptor (Sonolith 2000 Type B) in patients with upper urinary tract stones. The studies were carried out on 101 cases at the Departments of Urology, Juntendo University School of Medicine, Kanto Teishin Hospital and General Daiyukai Hospital from Nov. 1987 to Jun. 1988. The location of stones were renal calyx and pelvis in 84 cases, ureteropelvic junction in 7 cases and upper ureter in 12 cases (2 of them had multiple stones at different levels). The average number of treatment per a patient was 1.25, and that of shock waves delivered per treatment was 1798. Ultrasound localization has been effective in all cases. The rate of destruction of the stones was 100% in the kidney, 66.7% in the upper ureter, with an overall average of 95.0%. On the X-ray film obtained six weeks after ESWL treatment, the stone free rate was 53.5%, and the effectiveness rate was 89.1%, including the cases of stone free and cases with fragments smaller than 5 mm. No serious adverse effect was observed, although there were mild transient hematuria in all cases and pyrexia (more than 38.0 degrees C) in 7 cases (6.9%). The procedure was performed safely in the majority of patients without anesthesia. In 10 cases, we applied anesthesia (epidural anesthesia in 3 cases, and local anesthesia in 7 cases) for the prevention of pain. It is concluded that ESWL treatment using Sonolith 2000 Type B is as effective as other types of shock wave lithotriptor previously applied to urolithiasis without serious clinical complication.     

Peculiarity of pulsed dye laser lithotriptor and its clinical application

Ultrasound lithotriptors (USL) and electrohydraulic lithotriptors (EHL) are representative lithotriptors for endoscopic elimination of upper urinary tract stones. However, they have some disadvantages. For example, USL can not be used with flexible scopes and EHL can cause unexpected tissue injury. To overcome these problems, the pulsed dye laser lithotriptor (MDL-1, Candera Co.) was developed. The characteristics of this laser lithotriptor and its direct effects on tissue was investigated. This pulsed dye laser lithotriptor generates a 504 nm wavelength green light beam by using a combination of a xenon flash lamp and the greenish dye composed of coumarin solution. The maximum output energy is 60 mJ/pulse and the pulse duration is 1.5 microsecond. The pulse rate can be varied from 1 to 20 Hz. First, the intensity of the shock wave was measured by using a combination of a piezoelectric element and an oscilloscope, and then, the results were compaired with those obtained by a similar experiment with an EHL. The average intensity of the shock wave was 54.4 mW under the conditions of 40 mJ/pulse of output energy and 10 Hz of pulse duration. On the other hand, the EHL generated an average of 54.7 W under the conditions of 400 mJ/pulse output energy. Then, fragmentation of various kinds of urinary stones in saline solution was performed. The results showed that this lithotriptor could fragment almost all kinds of stones except cystine stones. Then, hen's eggs were used to observe the effect if laser bean influenced on the organism immediately behind the photoradiated object. Only the egg shell was demolished but the egg membrane below the eggshell did not undergo any change. After these experiments, skin, liver, kidney and urinary bladder of nude mice and human prostatic urethral mucosa in case of TUR-P were irradiated by this laser. The results showed that laser energy caused slight penetration and localized hemorrhage from the surface of epithelium to subcutaneous tissue. It was confirmed that these effects were generated when the tip of the quartz fiber was in direct contact with the object.(ABSTRACT TRUNCATED AT 250 WORDS)     

IMAGE BASED RENAL STONE TRACKING TO IMPROVE EFFICACY IN EXTRACORPOREAL LITHOTRIPSY

Purpose

We describe a method to reduce the number of shocks necessary to fragment renal stones during extracorporeal shock wave lithotripsy by automatically taking into account stone movements.

Materials and Methods

Echotrack computer software was developed and implemented on a lithotriptor. One software module uses image processing to detect instantaneous stone location based on ultrasound images generated by the lithotriptor. A second module uses the detected location to control the shock wave generator position, and automatically adjusts it to improve coincidence between the focal volume and stone. The reliability of the tracking algorithm was clinically tested in 65 patients with renal stones. These in vivo tests were qualitative and the goal was to assess software ability to track stones during actual treatments. A quantitative evaluation of the reduction in shocks necessary for fragmentation was performed in vitro. Artificial stones were moved according to computer generated trajectories. Each trajectory was applied once with and once without automatic adjustment of the generator position.

Results

The in vivo tests demonstrated software ability to track stones as far as they were visible in the images. During in vitro tests automatic adjustments of the generator position reduced the number of shocks necessary to fragment stones completely by a factor of 1.64.

Conclusions

Image based renal stone tracking software that automatically adjusts the shock wave generator position according to the displacement of renal stones is useful during extracorporeal shock wave lithotripsy. Treatment time was significantly shorter with this software.     

Optimization of the Erbium:YAG laser for precise incision of ureteral and urethral tissues: in vitro and in vivo results

BACKGROUND AND OBJECTIVES: Tissue damage during endoscopic treatment of urethral and ureteral strictures may result in stricture recurrence. The Erbium:YAG laser ablates soft tissues with minimal peripheral damage and may be a promising alternative to cold knife and Holmium:YAG laser for precise incision of urological strictures. STUDY DESIGN/MATERIALS AND METHODS: Optimization of the Er:YAG laser was conducted using ex vivo porcine ureteral and canine urethral tissues. Preliminary in vivo studies were also performed in a laparoscopic porcine ureteral model with exposed ureter. Laser radiation with a wavelength of 2.94 microm, pulse lengths of 8, 70, and 220 microseconds, output energies of 2-35 mJ, fluences of 1-25 J/cm2, and pulse repetition rates of 5-30 Hz, was delivered through 250-microm and 425-microm core germanium oxide optical fibers in direct contact with tissue. RESULTS: Ex vivo perforation thresholds measured 2-4 J/cm2, with ablation rates of 50 microm/pulse at fluences of 6-11 J/cm2. In vivo perforation thresholds were approximately 1.8 J/cm2, with the ureter perforated in less than 20 pulses at fluences greater than 3.6 J/cm2. Peripheral thermal damage in tissue decreased from 30 to 60 microm to 10-20 microm as the laser pulse length decreased from 220 to 8 microseconds. Mechanical tissue damage was observed at the 8 microseconds pulse duration. CONCLUSIONS: The Er:YAG laser, operating at a pulse duration of approximately 70 microseconds, a fluence greater than approximately 4 J/cm2, and a repetition rate less than 20 Hz, is capable of rapidly incising urethral and ureteral tissues with minimal thermal and mechanical side-effects.     

Comparison of methods for transcatheter fragmentation of gallstones

Summary Alternative methods have been considered for treating cholelithiasis. Compared to extracorporeal shockwave lithotripsy (ESWL), a percutaneous endoscopic approach would be more invasive, but would offer the advantage of immediate stone removal without the need for subsequent drug therapy. We performed an in vitro comparison of three methods of transcatheter cholecystolithotripsy with regard to effectiveness of stone fragmentation, damage to the gallbladder mucosa, and compatibility with percutaneous delivery systems. The three devices used for cholecystolithotripsy were the ultrasonic lithotriptor (UL), the electrohydraulic lithotriptor (EHL), and the thulium-holmium-chromium: YAG laser (THC:YAG). The UL effectively fragmented all types of stones studied, although it is necessary to hold the stone against the tip of the probe. The EHL quickly fragmented noncalcified and pigment stones simply by placing the tip in the vicinity of the stone, but calcified stones had to be held in position near the electrode. The THC:YAG was effective at fragmenting each type of stone, but the number of pulses required was quite large, corresponding to 7 min for some stones. The EHL had the most capacity for mucosal damage, followed by the THC:YAG laser. The UL produced no mucosal damage at the exposure times tested. The UL is not compatible with flexible endoscopes while the EHL and the THC:YAG are. Because of the specific advantages and disadvantages of each device, a combination of devices may be required for successful clinical cholecystolithotripsy.     

Stone fragility--measurement of stone mineral content by dual photon absorptiometry.

We measured the mineral content of urinary tract stones by dual photon absorptiometry, which is widely used for the analysis of bone mineral content, and compared the values of the stones by dual photon absorptiometry (DPA values) with the results of an in vitro fracture study as well as those of an in vivo extracorporeal shock wave lithotripsy treatment study. The results of a preliminary experiment showed that the DPA values of 20 urinary tract stones reflected actual stone mineral content. As a result of the in vitro fracture study, the DPA value calculated by volume of a struvite stone, which was the most easily disintegrated, was the lowest (0.53 g/cm3). The DPA values of calcium oxalate monohydrate and apatite stones, which poorly disintegrated, were the highest (0.98, 1.01 g/cm3). The DPA value of calcium oxalate dihydrate, which moderately disintegrated, was 0.86 g/cm3. By the in vivo extracorporeal shock wave lithotripsy treatment study, the total DPA values of stones measured before extracorporeal shock wave lithotripsy treatment in 12 patients were 0.73 +/- 0.34 g in successful cases and 1.92 +/- 0.43 g in unsuccessful cases with a significant difference between the two (p less than 0.05). These results showed that the measurement of stone mineral content by dual photon absorptiometry was useful in predicting the fragility of stones against shock waves before performing extracorporeal shock wave lithotripsy treatment for patients with urinary tract stones.     

Edge targeting reduces the number of shock waves required for biliary ESWL in vitro

In vitro experiments were conducted to determine if differences in targeting would effect stone fragmentation. Ten pairs of twin gallstones were used. The stones in each pair were identical in volume, diameter, radiolucency, and gross shape. One stone from each pair was subjected to shock waves focused at the center of the stone; the other was treated with shock waves targeted at the edge. Lithotripsy was terminated when all fragments were less than 5mm in diameter. The total number of shock waves used for each stone was recorded. In 7 of 10 pairs, fewer shock waves were required to fragment the edge targeted stone than the center targeted stone. In two of the remaining three pairs, equal numbers of shock waves were required for complete fragmentation. The difference between edge targeting and center targeting was shown to be statistically significant using the nonparametric Wilcoxin Signed Rank Test. (1 tailed = p less than 0.02, 2 tailed = p less than 0.04). These findings suggest that the outcome of biliary lithotripsy may be improved by targeting the edge of the stone.     

Acoustic and mechanical properties of artificial stones in comparison to natural kidney stones

PURPOSE: Standardized and reproducible artificial kidney stone models are important for performing comparative studies of different lithotripsy modalities. The acoustic and mechanical properties of renal calculi dictate the manner by which stones interact with the mechanical stresses produced by shock wave lithotripsy (SWL) or intracorporeal lithotripsy modalities. We have developed a novel artificial kidney stone model that is made of natural substances found in real kidney stones. These stone models appear to be much closer in physical properties to natural kidney stones than previously used stone models. MATERIALS AND METHODS: The acoustic and mechanical properties of six groups of artificial stone models were compared to corresponding natural stones of similar compositions. Moreover, three groups of artificial stone models made of plaster-of-Paris were compared to their natural counterparts. In terms of acoustic properties, stone density was measured using a pycnometer based on Archimedes' principle, whereas longitudinal and transverse (or shear) wave propagation speeds were measured using an ultrasound pulse transmission technique. These values were used to calculate wave impedance and dynamic mechanical properties (bulk modulus, Young's modulus, and shear modulus) of the stones. The microhardness of the stones was measured and the effect of composition on stone fragility was evaluated. RESULTS: Artificial stones, when compared to natural stones of similar composition, showed similar trends in longitudinal and transverse wave speeds, wave impedance, and dynamic elastic moduli. However, values for the artificial stones were uniformly low compared to those of natural stones, suggesting that these artificial stones may be more amenable to shock wave fragmentation. The results of SWL on stone fragmentation of artificial and natural stones also revealed similar trends with the exception of artificial cystine stones which were found to be the most resistant to shock wave fragmentation. CONCLUSIONS: The results indicate that the physical properties of artificial stones made of natural stone materials are comparable to renal calculi of the same chemical composition. The data suggests that these stone phantoms are suitable for performing standardized and reproducible in vitro investigations, especially with regards to fragility of kidney stones of different chemical compositions during SWL.     

Extracorporeal shock wave lithotripsy for urinary tract stones using MPL 9000 spark gap technology and ultrasound monitoring

Between November 7, 1988 and December 31, 1989, 881 treatments were given with the MPL 9000 lithotriptor to 513 sites in 510 renal units in 464 patients. Of the stones 447 (87.1%) were in the kidney, 64 (12.5%) in the ureter and 2 (0.4%) in the bladder. Stone size was up to 2 cm. in 58.5% of the cases, greater than 2 to 3 cm. in 25.8% and more than 3 cm. in 15.7%, including complete or partial staghorn, or multiple stones. Of the patients 54.2% received only 1 treatment, 17.6% received 2 treatments and 28.2% received more than 2 treatments (re-treatment was necessary in 45.8%). The number of shocks used varied from 610 to 4,000 at 14 to 24 kv., the usual energy used being 18 kv. Of the stones 30.2% were treated after Double-J stents were inserted. A patient was declared stone-free only when no stone particle was visible on a plain abdominal x-ray (or ultrasound if the stone was radiolucent). X-rays 3 months after extracorporeal shock wave lithotripsy (ESWL) were available for review in 397 patients (79.9%) and 72.8% were stone-free (with the aforementioned criteria) at 6 months (61.5% without ancillary procedures and 11.3% after ancillary procedures). Of a subset of 106 patients 84% were stone-free within 3 months when ESWL was restricted to a smaller stone burden, the number of shock waves administered was increased and energy was restricted to 14 to 18 kv. Over-all, 9.1% of the patients needed ancillary measures, including percutaneous nephrostomy in 1.6%, push-back for ESWL in 1.9%, ureterorenoscopy in 5.4%, percutaneous nephrolithotomy in 0.6% and pyelolithotomy/ureterolithotomy in 2.8%. The MPL 9000 device has the unique combination of electrohydraulic shock wave generation and ultrasound monitoring. The latter attribute has the distinct advantage of avoiding radiation to allow for visualization of nonopaque renal and gallbladder calculi. In addition, because there is continuous stone visualization during fragmentation accurate stone targeting can be maintained. The combination of ultrasound monitoring and spark gap technology allows for effective stone fragmentation.     

Acute morphological changes in canine kidneys after exposure to extracorporeal shock waves

Summary The acute effects of extracorporeal shock waves on renal morphology were studied by light and electron microscopy in 14 dogs. One kidney received an average clinical number of exposures, the nonexposed, contralateral kidney serving as control. The original Dornier HM-3 generator was used in 3 animals, the modified version in 11. Intravascular radiographic contrast medium was administered in five animals. Damage was observed in all exposed kidneys, none in the contralateral control kidney. The effects were characterized by renal and perirenal hemorrhage and edema, parenchymal hemorrhagic foci with tissue destruction, often extending from cortex to medulla. In the nearby regions there was endothelial cell damage in arteries, veins and glomerular capillaries. Breaks in the wall of these vessels were detected with platelet plug formations and thrombi. In glomeruli, breaks of Bowman's capsule and epithelial cell damage with loss of foot processes were observed. A wide range of tubular cell damage was demonstrated, ranging from vacuolization to complete necrosis. Tubular lumina were filled with red cells, indicating renal origin of hematuria. The tissue damage was less pronounced in kidneys exposed to the modified lithotriptor than to the original. No difference in the quantity or quality of damage was detected whether radiographic contrast medium was administered or not.     

Results of EDAP lithotriptor treatment of kidney stones in our first fifty patients

We report the results of the treatment of the first 50 patients with the EDAP lithotriptor at our center. The EDAP is a second generation lithotriptor that employs ultrasound imaging and piezo-electric energy stone fragmentation. Seventy-six percent of patients had kidney stones completely eliminated or residual no greater than 3 mL. Fourteen percent of patients had residual fragments which may require second treatment. Five stones showed no improvement, and 2 stones could not be imaged. Only 2 patients required anesthesia. One patient required hospitalization prior to treatment. The rest were treated as outpatients. This preliminary FDA-investigative study limited our protocol to stones of 0.5 cm to 2.5 cm within the kidney or proximal ureter. Since particles passed were so small, "steinstrasse phenomenon" (distal ureteral obstruction by stone fragments) was not encountered and routine stent placement was obviated. There were no major complications.     

The effect of treatment strategy on stone comminution efficiency in shock wave lithotripsy

PURPOSE: The comminution of kidney stones in shock wave lithotripsy (SWL) is a dose dependent process caused primarily by the combination of 2 fundamental mechanisms, namely stress waves and cavitation. The effect of treatment strategy with emphasis on enhancing the effect of stress waves or cavitation on stone comminution in SWL was investigated. Because vascular injury in SWL is also dose dependent, optimization of the treatment strategy may produce improved stone comminution with decreased tissue injury in SWL. MATERIALS AND METHODS: Using an in vitro experiment system that mimics stone fragmentation in the renal pelvis spherical BegoStone (Bego USA, Smithfield, Rhode Island) phantoms (diameter 10 mm) were exposed to 1,500 shocks at a pulse repetition rate of 1 Hz in an unmodified HM-3 lithotripter (Dornier Medical Systems, Kennesaw, Georgia). The 3 treatment strategies used were increasing output voltage from 18 to 20 and then to 22 kV every 500 shocks with emphasis on enhancing the effect of cavitation on medium fragments (2 to 4 mm) at the final treatment stage, decreasing output voltage from 22 to 20 and then to 18 kV every 500 shocks with emphasis on enhancing the effect of stress waves on large fragments (greater than 4 mm) at the initial treatment stage and maintaining a constant output voltage at 20 kV, as typically used in SWL procedures. Following shock wave exposure the size distribution of fragments was determined by the sequential sieving method. In addition, pressure waveforms at lithotripter focus (F2) produced at different output settings were measured using a fiber optic probe hydrophone. RESULTS: The rate of stone comminution in SWL varied significantly in a dose dependent manner depending on the treatment strategies used. Specifically the comminution efficiencies produced by the 3 strategies after the initial 500 shocks were 30.7%, 59% and 41.9%, respectively. After 1,000 shocks the corresponding comminution efficiencies became similar (60.2%, 68.1% and 66.4%, respectively) with no statistically significant differences (p = 0.08). After 1,500 shocks the final comminution efficiency produced by the first strategy was 88.7%, which was better than the corresponding values of 81.2% and 83.5%, respectively, for the other 2 strategies. The difference between the final comminution efficiency of the first and second strategies was statistically significant (p = 0.005). CONCLUSIONS: Progressive increase in lithotripter output voltage can produce the best overall stone comminution in vitro.