Size and location of defects at the coupling interface affect lithotripter performance

2022 Recommendations of the AFU Lithiasis Committee: Extracorporeal shock wave lithotripsy (ESWL)

Extracorporeal shock wave lithotripsy (ESWL) is a minimally invasive technique for the fragmentation of urinary tract stones using shock waves under fluoroscopic and/or ultrasound guidance. ESWL results depend on the indication (stone size/composition, clinical context) and also on how it is performed. The stone structure, nature and density (Hounsfield units; evaluated by CT without contrast agent) influence the fragmentation achieved by ESWL. The upper size limit of kidney stones has been lowered to 15mm (1.68cm3) due to the increased risk of steinstrasse with larger sizes and the potential need of anesthesia and ureteral stenting. Conversely, the development of endourological technologies allows a finer stone fragmentation and/or better elimination, thus reducing the risk of steinstrasse and decreasing the potential number of sessions or additional interventions. METHODOLOGY: These recommendations were developed using two methods: the Clinical Practice Recommendations method (CPR) and the ADAPTE method, depending on whether the question was considered in the European Association of Urology (EAU) recommendations (https://uroweb.org/guidelines/urolithiasis [EAU 2022]) and their adaptability to the French context.

Renal Protection Phenomenon Observed in a Porcine Model After Electromagnetic Lithotripsy Using a Treatment Pause

Purpose: Pretreating the kidney with 100 low-energy shock waves (SWs) with a time pause before delivering a clinical dose of SWs (Dornier HM-3, 2000 SWs, 24 kV, and 120 SWs/min) has been shown to significantly reduce the size of the hemorrhagic lesion produced in that treated kidney, compared to a protocol without pretreatment. It has been assumed that a similar reduction in injury will occur with lithotripters other than the HM-3, but experiments to confirm this assumption are lacking. In this study, we sought to verify that the lesion protection phenomenon also occurs in a lithotripter using an electromagnetic shock source and dry-head coupling. Materials and Methods: Eleven female pigs were placed in a Dornier Compact S lithotripter where the left kidney of each animal was targeted for lithotripsy treatment. Some kidneys received 2500 SWs at power level (PL) = 5 (120 SWs/min) while some kidneys were pretreated with 100 SWs at PL = 1, with a 3-minute time pause, followed immediately by 2500 SWs at PL = 5 (120 SWs/min). Lesion size analysis was performed to assess the volume of hemorrhagic tissue injury created by each treatment regimen (% functional renal volume). Results: Lesion size fell by 85% (p = 0.01) in the 100 SW pretreatment group compared to the injury produced by a regimen without pretreatment. Conclusions: The results suggest that the treatment pause protection phenomenon occurs with a Dornier Compact S, a machine distinctly different from the Dornier HM-3. This result also suggests that this phenomenon may be observed generally in SW lithotripters.

Experimental observations and numerical modeling of lipid-shell microbubbles with calcium-adhering moieties for minimally-invasive treatment of urinary stones

A novel treatment modality incorporating calcium-adhering microbubbles has recently entered human clinical trials as a new minimally-invasive approach to treat urinary stones. In this treatment method, lipid-shell gas-core microbubbles can be introduced into the urinary tract through a catheter. Lipid moities with calcium-adherance properties incorporated into the lipid shell facilitate binding to stones. The microbubbles can be excited by an extracorporeal source of quasi-collimated ultrasound. Alternatively, the microbubbles can be excited by an intraluminal source, such as a fiber-optic laser. With either excitation technique, calcium-adhering microbubbles can significantly increase rates of erosion, pitting, and fragmentation of stones. We report here on new experiments using high-speed photography to characterize microbubble expansion and collapse. The bubble geometry observed in the experiments was used as one of the initial shapes for the numerical modeling. The modeling showed that the bubble dynamics strongly depends on bubble shape and stand-off distance. For the experimentally observed shape of microbubbles, the numerical modeling showed that the collapse of the microbubbles was associated with pressure increases of some two-to-three orders of magnitude compared to the excitation source pressures. This in-vitro study provides key insights into the use of microbubbles with calcium-adhering moieties in treatment of urinary stones.

Preliminary Report on Stone Breakage and Lesion Size Produced by a New Extracorporeal Electrohydraulic (Sparker Array) Discharge Device

OBJECTIVE

To determine if an innovative extracorporeal electrohydraulic shock wave (SW) device (sparker array [SPA]) can effectively fracture artificial stones in vitro and in vivo, and if SPA treatment produces a renal lesion in our pig model of lithotripsy injury. Results of these experiments will be used to help evaluate the suitability of this device as a clinical lithotripter.

MATERIALS AND METHODS

Ultracal-30 artificial stones were placed in a holder at the focus of the SPA and treated with 600 SWs (21.6 kV, 60 shocks/min). Stone fragments were collected, dried, and weighed to determine stone breakage. In vivo stone breakage entailed implanting stones into pigs. These stones were treated with 600 or 1200 SWs and the fragments were collected for analysis. Lesion analysis consisted of treating the left kidney of pigs with 1200 or 2400 SWs and quantitating the hemorrhagic lesion.

RESULTS

In vitro, 71% ± 2% of each artificial stone was fractured to <2 mm in size. In vivo stone breakage averaged 63%. Renal injury analysis revealed that only 1 of 7 kidneys showed evidence of hemorrhagic injury in the treated area.

CONCLUSION

The SPA consistently comminuted artificial stones demonstrating its ability to fracture stones like other lithotripters. Also, the SPA caused little to no renal injury at the settings used in this study. These findings suggest further research is warranted to determine the potential of this device as a clinical lithotripter.

Evaluation of an experimental electrohydraulic discharge device for extracorporeal shock wave lithotripsy: Pressure field of sparker array

In this paper, an extracorporeal shock wave source composed of small ellipsoidal sparker units is described. The sparker units were arranged in an array designed to produce a coherent shock wave of sufficient strength to fracture kidney stones. The objective of this paper was to measure the acoustical output of this array of 18 individual sparker units and compare this array to commercial lithotripters. Representative waveforms acquired with a fiber-optic probe hydrophone at the geometric focus of the sparker array indicated that the sparker array produces a shock wave (P⁺ ∼40-47 MPa, P^- ∼2.5-5.0 MPa) similar to shock waves produced by a Dornier HM-3 or Dornier Compact S. The sparker array's pressure field map also appeared similar to the measurements from a HM-3 and Compact S. Compared to the HM-3, the electrohydraulic technology of the sparker array produced a more consistent SW pulse (shot-to-shot positive pressure value standard deviation of ±4.7 MPa vs ±3.3 MPa).

A new optical coupling control technique and application in SWL

The objective of this study was to compare the results of shock wave lithotripsy (SWL) between patients treated with optical coupling control (OCC) and those treated with "blind" coupling during SWL to treat renal stones. Enrolled in the study were patients with urinary stones who underwent SWL between January 2014 and February 2015. The lithotripter used in the study was an electromagnetic Dornier Compact Delta II UIMS. The closed envelope method was used to randomize the enroled patients to OCC (Group A) or "Blind" coupling group (Group B). The stone-free rates (SFRs) were determined using KUB film with or without ultrasonography after 3 months. Treatment failure was defined as radiologically confirmed persistence of the stone with no fragmentation after second SWL sessions. Complications during the intraoperative or post-operative periods were recorded. A total of 336 patients satisfied the inclusion criteria for the study, of which 169 patients were treated in the Group A and 167 in the Group B. There was no significant difference in patient and stone characteristics between the two groups (Table 1). The locations of treated stones are shown in Table 2. The treatment results were stratified by stone location in Table 3, significant differences existed in all treatment results between the two groups (P < 0.05). The overall stone-free rates after 3 months were 78.2 % for kidney stones and 81.7 % for ureteral stones in patients from Group A. The corresponding SFRs for patients in Group B were 62.8 and 67.9 % for stones in the kidneys and ureters, respectively. There were statistical differences in these results between the two groups (P < 0.05). The lithotripter with OCC had excellent shock wave transmission properties with the least possible loss of energy; it can lead to the optimization of SWL treatment outcome and reduce the incidence of SW-induced adverse effects. We are confident that the OCC used in this study should be a standard feature in future lithotripters. Table 1 Patients' and stones' characteristics Group A Group B P value Number of patients 169 167 Patients' gender (M/F) 97/72 109/58 0.138 Stone location (left/right) 86/83 89/78 0.659 Patients' age (years) 36.3 ± 7.1 34.2 ± 6.8 0.521 Size of stones  Kidney (cm) 1.4 ± 0.6 1.3 ± 0.7 0.452  Ureter (cm) 1.1 ± 0.5 1.1 ± 0.4 0.354  Average size (cm) 1.2 ± 0.8 1.2 ± 0.7 0.372 Table 2 The distribution of location of stones treated Group A % Group B % Upper calyx 21 12.4 25 15.0 Middle calyx 28 16.6 23 13.8 Lower calyx 7 4.1 5 3.0 Renal pelvis 31 18.3 33 19.8 Upper ureter 28 16.6 31 18.6 Middle ureter 6 3.6 4 2.4 Lower ureter 48 28.4 46 27.5 Overall 169 100.0 167 100.0 Table 3 The treatment results were stratified by stone location Group A Group B %Stone-free %Re-treatment %Ancillary procedure %Stone-free %Re-treatment %Ancillary procedure Kidney  Upper calyx 76.2 33.3 14.3 60.0 48.0 12.0  Middle calyx 75.0 35.7 7.1 56.5 56.5 13.0  Lower calyx 71.4 42.9 28.6 60.0 60.0 40.0  Renal pelvis 83.9 29.0 9.7 69.7 45.5 12.1  Overall 78.2 33.3 11.5 62.8 50. 0 14.0 Ureter  Upper ureter 82.1 28.6 10.7 74.2 32.3 16.1  Middle ureter 66.7 66.7 33.3 50. 75.0 50.0  Lower ureter 83.3 25.0 10.4 65.0 41.3 13.0  Overall 81.7 29.3 12.2 67.9 39.5 16.0.

Extracorporeal shock wave lithotripsy in the treatment of renal and ureteral stones

The use of certain technical principles and the selection of favorable cases can optimize the results of extracorporeal shock wave lithotripsy (ESWL). The aim of this study is to review how ESWL works, its indications and contraindications, predictive factors for success, and its complications. A search was conducted on the Pubmed® database between January 1984 and October 2013 using "shock wave lithotripsy" and "stone" as key-words. Only articles with a high level of evidence, in English, and conducted in humans, such as clinical trials or review/meta-analysis, were included. To optimize the search for the ESWL results, several technical factors including type of lithotripsy device, energy and frequency of pulses, coupling of the patient to the lithotriptor, location of the calculus, and type of anesthesia should be taken into consideration. Other factors related to the patient, stone size and density, skin to stone distance, anatomy of the excretory path, and kidney anomalies are also important. Antibiotic prophylaxis is not necessary, and routine double J stent placement before the procedure is not routinely recommended. Alpha-blockers, particularly tamsulosin, are useful for stones >10mm. Minor complications may occur following ESWL, which generally respond well to clinical interventions. The relationship between ESWL and hypertension/diabetes is not well established.

Lithotripter outcomes in a community practice setting: comparison of an electromagnetic and an electrohydraulic lithotripter

PURPOSE

We assessed patient outcomes using 2 widely different contemporary lithotripters.

MATERIALS AND METHODS

We performed a consecutive case series study of 355 patients in a large private practice group using a Modulith® SLX electromagnetic lithotripter in 200 patients and a LithoGold LG-380 electrohydraulic lithotripter (TRT, Woodstock, Georgia) in 155. Patients were followed at approximately 2 weeks. All preoperative and postoperative films were reviewed blindly by a dedicated genitourinary radiologist. The stone-free rate was defined as no residual fragments remaining after a single session of shock wave lithotripsy without an ancillary procedure.

RESULTS

Patients with multiple stones were excluded from analysis, leaving 76 and 142 treated with electrohydraulic and electromagnetic lithotripsy, respectively. The stone-free rate was similar for the electrohydraulic and electromagnetic lithotripters (29 of 76 patients or 38.2% and 69 of 142 or 48.6%, p = 0.15) with no difference in the stone-free outcome for renal stones (20 of 45 or 44.4% and 33 of 66 or 50%, p = 0.70) or ureteral stones (9 of 31 or 29% and 36 of 76 or 47.4%, respectively, p = 0.08). The percent of stones that did not break was similar for the electrohydraulic and electromagnetic devices (10 of 76 patients or 13.2% and 23 of 142 or 16.2%) and ureteroscopy was the most common ancillary procedure (18 of 22 or 81.8% and 30 of 40 or 75%, respectively). The overall mean number of procedures performed in patients in the 2 groups was similar (1.7 and 1.5, respectively).

CONCLUSIONS

We present lithotripsy outcomes in the setting of a suburban urology practice. Stone-free rates were modest using shock wave lithotripsy alone but access to ureteroscopy provided satisfactory outcomes overall. Although the acoustic characteristics of the electrohydraulic and electromagnetic lithotripters differ substantially, outcomes with these 2 machines were similar.

Optical coupling control: an important step toward better shockwave lithotripsy

BACKGROUND

In modern "dry" lithotripters, shockwaves are generated in a membrane-covered water cushion that is then coupled to the patient.To limit energy loss, a coupling agent, usually ultrasound gel, is used in this acoustic interface. During the coupling process, air pockets are inevitably trapped in the coupling area, which subsequently remains invisible to the operator. These air pockets dramatically decrease stone fragmentation efficiency up to 40%.

MATERIALS AND METHODS

To check for air bubbles in the coupling interface, a video camera was installed in the therapy head of our Dornier Gemini lithotripter: all air bubbles observed in the coupling zone could then be removed under visual control. We evaluated the effect of this optically controlled coupling (OCC) on treatment results (10/1/12-9/30/13) and compared these to the results obtained in a "blind" coupling mode (4/1/11-4/30/12).

RESULTS

Optically controlled removal of air bubbles from the coupling area reduced the required number of shockwaves with 25.4% for renal stones and 25.5% for ureteral stones. Energy level was reduced by 23.1% for renal stones and by 22.5% for ureteral stones. For renal stones, total applied energy was thus reduced by 42.9%. Effectiveness quotients were comparable.

CONCLUSIONS

Optical control with a video camera proved pivotal in the realization of bubble-free coupling. Bubble-free coupling significantly reduced the total energy needed to obtain comparable treatment results. Theoretically, this should also lead to a reduced incidence and severity of shockwave-induced adverse effects. We consider this an important step toward better and safer shockwave lithotripsy and would therefore advocate the standard incorporation of an OCC system in all new lithotripters.

Effect of the body wall on lithotripter shock waves

PURPOSE

Determine the influence of passage through the body wall on the properties of lithotripter shock waves (SWs) and the characteristics of the acoustic field of an electromagnetic lithotripter.

METHODS

Full-thickness ex vivo segments of pig abdominal wall were secured against the acoustic window of a test tank coupled to the lithotripter. A fiber-optic probe hydrophone was used to measure SW pressures, determine shock rise time, and map the acoustic field in the focal plane.

RESULTS

Peak positive pressure on axis was attenuated roughly proportional to tissue thickness-approximately 6% per cm. Irregularities in the tissue path affected the symmetry of SW focusing, shifting the maximum peak positive pressure laterally by as much as ∼2 mm. Within the time resolution of the hydrophone (7-15 ns), shock rise time was unchanged, measuring ∼17-21 ns with and without tissue present. Mapping of the field showed no effect of the body wall on focal width, regardless of thickness of the body wall.

CONCLUSIONS

Passage through the body wall has minimal effect on the characteristics of lithotripter SWs. Other than reducing pulse amplitude and having the potential to affect the symmetry of the focused wave, the body wall has little influence on the acoustic field. These findings help to validate laboratory assessment of lithotripter acoustic field and suggest that the properties of SWs in the body are much the same as have been measured in vitro.

Optimizing shock wave lithotripsy: a comprehensive review

Shock wave lithotripsy is a commonly used procedure for eradicating upper urinary tract stones in patients who require treatment. A number of methods have been proposed to improve the results of this procedure, including proper patient selection, modifications in technique, adjunctive therapy to facilitate elimination of fragments, and changes in lithotripter design. This article assesses the utility of these measures through an analysis of contemporary literature.