Stone Ablation Rates Research Articles

Steady-state versus burst lasing techniques for thulium fiber laser

ObjectiveTo evaluate the stone ablation rate and direct thermal damage from thulium fiber laser (TFL) lithotripsy using continuous (C) and burst (B) lasing techniques on an in vitro ureteral model.MethodsThe TFL Drive (Coloplast, Humlebaek, Denmark) was used in an in vitro saline-submerged ureteral model. Ten participants, including five junior and five experienced urologists, conducted the experimental setup with 7 different settings comparing two lasing techniques: steady-state lasing (0.5 J/10 Hz = 5W for 300 s and 0.5 J/20 Hz = 10W for 150 s) and burst, intermittent 5 s on/off lasing (0.5 J/20 Hz, 0.5 J/30 Hz, 0.5 J/60 Hz, 0.1 J/200 Hz, and 0.05 J/400 Hz) with a target cumulative energy of 1500 J using cubic 125 mm3 phantom BegoStonesTM. Ureteral damage was graded 1–3 based on the severity of burns and holes observed on the surface of the ureteral model.ResultsThe were no significant differences in stone ablation mass neither between C and B lasing techniques, nor between expertise levels. At C lasing technique had only mild ureteral lesions with no significant differences between expertise levels (p: 0.97) or laser settings (p: 0.71). At B lasing technique, different types of thermal lesions were found with no expertise (p: 0.11) or setting (p: 0.83) differences. However, B laser setting had higher grade direct thermal lesions than C (p: 0.048).ConclusionRegarding efficacy, C and B lasing techniques achieve comparable stone ablation rates. Safety-wise, B lasing mode showed higher grade of direct thermal lesions. These results should be further investigated to verify which of the lasing mode is the safest in vivo. Until then and unless proven otherwise, a C mode with low frequency should be recommended to avoid ureteral wall lesions.

Realizing enhanced lithotripsy efficiency using 700 W peak power thulium-doped fiber laser

Despite its widespread use in laser lithotripsy, the Ho:YAG solid-state laser suffers from limited parameter combinations, poor beam quality, and low photoelectric conversion efficiency. The development of 2.0 μm fiber laser technology has positioned the thulium-doped fiber laser (TFL) as a superior alternative to the Ho:YAG laser in lithotripsy. The TFL excels because of its high-water absorption coefficient, all-fiber structure and pump modulation flexibility. However, the peak power reported for TFL in lithotripsy remains at most 500 W. This study presented a quasi-continuous wave (QCW) TFL featuring a wide tunable range of pulse width and pulse repetition rates, and a peak power of 700 W to realize enhanced ablation efficiency. A high-speed camera was used to acquire the laser-induced cavitation bubble images for the analysis of the interaction mechanism of a high peak power QCW TFL pulse with water and stones. While the synergistic action of photothermal and photomechanical effects constituted the mechanism of TFL lithotripsy, the laser-induced bubble channel was a prerequisite for TFL noncontact effective lithotripsy, with bubble length and width markedly influencing stone ablation rates. Ablation experiments on uric acid and calcium oxalate monohydrate stones conducted with various parameter combinations at a peak power of 700 W yielded rates of 8.9 mg/s for uric acid stones and 7.5 mg/s for calcium oxalate monohydrate stones. A comparison with prior findings confirmed that a high peak power TFL could notably improve stone ablation rates.

Assessment of stone ablation rate using the Moses technology modes with different energy and pulse settings: An experimental study

ABSTRACT Objectives To compare lithotripsy ablation rate with the Moses modes versus conventional pulse modes when using the Holmium:Yttrium–Aluminum–Garnet (Ho:YAG) laser. Methods The Lumenis® Pulse P120H Holmium Laser System and a 365 μm Moses D/F/L fiber were used to assess stone ablation rate in conventional Short and Long Pulse as well as Moses Contact and Distance at 10 W (0.5Jx20Hz and 2Jx5Hz) and 60 W (1Jx60Hz and 2Jx30Hz). Hard and soft phantom stones were formed, and all tests were conducted in a custom experimental configuration installed in a saline-filled bath. The laser was delivered up to 3 kJ of total energy. The fragmentation pattern was assessed via photographs in each cohort. Results The time to reach the target energy was 5 min and 50 s in all 10 W and 60 W trials, respectively. In both stone types, ablation was more effective when high-power, high-energy and Moses Distance was utilized. In soft stones, the lowest ablation rate was detected in the Long Pulse modality in all power, energy and frequency settings. Overall, when dusting settings (high-frequency, low-energy) were used, a deeper single cavitation was observed rather than small cavitations. Conclusions The most effective pulse modality as evaluated via stone ablation rate depends on the stone hardness as well as energy and frequency settings. In both hard and soft stones, ablation is more effective when 60 W (2Jx30Hz) power settings and Moses Distance are used. Tailored laser settings in terms of energy and frequency could be set for each case scenario.

Urinary stone ablation with a thulium fibre laser: a rate-of-completion evaluation

Introduction. The main disadvantage of using the rate of ablation of urinary stones as a parameter of thulium lithotripsy is the dependence of this parameter on the energy and frequency of laser pulses. Therefore, the results of measurements of this parameter by researchers differ significantly, since they were carried out at different values of the energy and pulse frequency, as well as at different values of the radiographic density of stones.Objective. To develop a universal indicator to assess the specific value of reducing the mass of urinary stones when performing laser lithotripsy.Materials & methods. We have analyzed scientific publications in domestic and foreign specialized publications (2005 to 2023) related to the measurement of urinary stone ablation rate during thulium laser lithotripsy. We used physical methods of estimation of specific values when we developed a universal indicator of specific value of stone mass reduction.Results. Having processed the data, we obtained the average value of the specific indicator of urinary stone mass reduction per unit of pulse energy during thulium lithotripsy in the ‘dusting mode’, equal to 0.059 ± 0.003 mg/J. The article provides a formula for calculating the "pure" time of lithotripsy, as well as examples of calculating the specific indicator of the stone mass reduction and the time of lithotripsy.Conclusion. This value can be used both to evaluate the efficiency of thulium laser lithotripsy and to predict the time of lithotripsy.

Enhanced popcorning using polyanionic chelating solutions as irrigation.

Poly-anionic compounds can chelate divalent cations and dissolve calcium oxalate stone. Our objective was to assess how much concurrent irrigation with poly-anionic chelating solutions during non-contact laser lithotripsy or popcorning could improve stone ablation rate. A popcorning model was created by lowering a ureteroscope with thulium fiber laser into a test tube calyx. Begostones of matching size and mass were placed in the test tube and treated with the laser while irrigating with different iso-osmolar poly-anionic solutions. We compared 0.9% sodium chloride (NaCl), sodium citrate, sodium hexa-metaphosphate, and sodium ethylenediaminetetraacetate (EDTA) solutions. After treatment, residual stones were passed through a 1mm sieve, and remaining fragments greater than 1mm were weighed as remaining stone mass. Average remaining stone mass after lithotripsy with NaCl irrigation was 27.8% (± 10.0%). The average remaining stone mass after lithotripsy with hexa-metaphosphate, sodium citrate, and EDTA irrigation was 28.9% (± 13.4%), 17.5% (± 10.5%), and 9.8% (± 5.7%) respectively. Compared with NaCl, there was a 37% reduction in remaining stone mass when using citrate (p = 0.008) and a 64.7% reduction when using EDTA irrigation during lithotripsy (p < 0.001). Concurrent irrigation with citrate or EDTA solutions synergistically enhances the efficacy laser lithotripsy in this in vitro popcorning model. This may lead to tangible improvements in endoscopic stone removal outcomes; however, the effectiveness on different stone types and safety during short duration lithotripsy should be further investigated.

Stone ablation efficacy: a comparison of a thulium fibre laser and two pulse-modulated holmium:YAG lasers

We present preliminary stone ablation rate results from an automated bench model using two pulse-modulated Ho:YAG lasers and a thulium fibre laser (TFL) in contact and non-contact modes. Ablation rate was assessed using automated apparatus that moved the laser fibre across flat BegoStone phantoms at a constant stone-to-fibre working distance (WD). Pre-soaked and unsoaked stones were used. A range of powers (20–60 W) was tested at WD of up to 3 mm. In pseudocontact, the prototype Ho:YAG laser produced higher ablation than the reference Ho:YAG laser at all powers tested (p < 0.002), and higher ablation than TFL at 20 W and 40 W (p < 0.001). At distance, ablation rates for the prototype were higher than the reference Ho:YAG laser using pre-soaked stones at WD up to 3 mm (p < 0.001). TFL required the laser fibre to be moved faster (5–12 mm/s) for optimal ablation, compared to 1–3 mm/s for the Ho:YAG lasers. TFL was unable to demonstrate ablation with unsoaked BegoStone. At any given power, similar ablation rates were achievable with all three lasers under optimised conditions. Novel pulse-modulation modes demonstrated higher ablation rates than the reference Ho:YAG laser’s pulse-modulation at a range of powers and WDs. Ablation rate of Ho:YAG lasers decreased linearly with WD whereas the ablation rate of TFL decreased rapidly beyond 2 mm WD. TFL was more affected by scan speed and pre-soaking of stone than Ho:YAG lasers. Ho:YAG lasers may be more practical in clinical settings because they are less dependent on ablation technique.

Holmium: Yttrium-aluminum-garnet laser lithotripsy: Is there a difference in ablation rates between short and long pulse duration?

The high-power holmium: yttrium-aluminum-garnet lasers provide a wide variety of settings for stone disintegration. The aim of this in vitro study is to evaluate the effect of short and long pulse duration on ablation rates on urinary stones. Two types of artificial stones were created by BegoStone™ with different compositions (15:3 and 15:6, stone/water ratio). Stones with a 15:3 and 15:6 powder-to-water ratio were defined as hard and soft stones, respectively. Lithotripsy was performed with different laser settings using a custom-made in vitro model consisting of a 60 cm long and 19 mm diameter tube. The ablation rate is defined as the final total mass subtracted from the initial total mass and divided to the time of treatment. Stone ablation rates were measured according to different laser settings with total power of 10W (0,5J-20 Hz, 1J-10 Hz, 2J-5 Hz) and 60W (1J-60 Hz, 1,5J-40 Hz, 2J-30 Hz). Higher pulse rates and higher total power settings were related to higher ablation rates. Short pulse duration was more effective on soft stones, whereas long pulse duration was more effective on hard stones. For the same power settings, the highest energy-lowest frequency combination resulted in higher ablation rate in comparison to the lowest energy-higher frequency combination. Finally, short and long pulse average ablation rates do not differ so much. Regardless of the stone type and pulse duration, utilization of higher power settings with higher energies increased the ablation rates. Higher ablation rates were demonstrated for hard stones using long pulse duration, and for soft stones with short pulse duration.

This Month in Adult Urology.

This Month in Adult Urology.

Thermal Injury and Laser Efficiency with Holmium YAG and Thulium Fiber Laser-An In Vitro Study.

Objective: To evaluate using an inanimate model the thermal injury and laser efficiency on high frequency, high energy, and its combination in hands of junior and experienced urologists during holmium YAG (Ho:YAG) and Thulium fiber laser (TFL) lithotripsy. Methods: A Cyber: Ho 150 WTM and Fiber Dust TFL (Quanta System) with 200 μm core-diameter laser fibers (LF) were used in a saline in vitro ureteral model. Each participant (five junior and five experienced urologists) performed 32 sessions of 5-minute lasering (125 mm3 phantom BegoStones™), comparing four modes (3 J/5 Hz [1.5 W], 0.3 J/20 Hz [6 W], 1.2 J/5 Hz [6 W], and 1.2 J/20 Hz [24 W]). Transparent tip and cleaved LF, and digital and fiberoptic ureteroscopes were also compared. Ureteral damage was classified in a scale (0-5) according to the burns and holes seen in the ureteral model's surface. Results: High-power (HP) setting (24 W) was associated with higher delivered energy and higher ablation rates (ARs) in both lasers (p < 0.001). For the same power setting (6 W), there was no difference in delivered energy or stone ARs. Regardless the settings, a higher AR was observed with TFL than with Ho:YAG (0.5Δ mg/s ± 0.33 vs 0.39 Δmg/s ± 0.31, p = 0.002) laser. Higher mean AR was found with cleaved tip vs transparent tip (p = 0.03) in TFL. For both lasers, higher ureteral damage was observed in the 24 W group (p = 0.006) and in the junior urologists (p = 0.03). Between 6 W groups, different types of lesions were found and junior urologist have more lesions when high frequency was used, for both Ho:YAG (p = 0.05) and TFL (p = 0.04). Conclusion: More stone ARs and reduced operative time are observed in HP settings; however, more ureteral thermic-related damage is produced. When comparing the same power, higher energy or frequency does not modify the AR. Nonetheless, more ureteral thermic-related thermal damage is observed in high-frequency settings in unexperienced hands.

PD55-10 MOSES 2.0 LASER IMPACT ON INTRAOPERATIVE PARAMETERS

You have accessJournal of UrologyCME1 May 2022PD55-10 MOSES 2.0 LASER IMPACT ON INTRAOPERATIVE PARAMETERS Samuel Antoine, Kerri Thurmon, Michael Atwell, Xavier Glover, Miguel Rodriguez-Homs, Fernando Kim, and Rodrigo Donalisio da Silva Samuel AntoineSamuel Antoine More articles by this author , Kerri ThurmonKerri Thurmon More articles by this author , Michael AtwellMichael Atwell More articles by this author , Xavier GloverXavier Glover More articles by this author , Miguel Rodriguez-HomsMiguel Rodriguez-Homs More articles by this author , Fernando KimFernando Kim More articles by this author , and Rodrigo Donalisio da SilvaRodrigo Donalisio da Silva More articles by this author View All Author Informationhttps://doi.org/10.1097/JU.0000000000002635.10AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookLinked InTwitterEmail Abstract INTRODUCTION AND OBJECTIVE: The Moses 2.0 laser was introduced to our hospital this year. The pulse-delivery technology increases energy transmission at each working distance. Frequency can be performed as high as 120 Hz which could improve stone dusting times, and energy levels can be performed up to 6 J which could improve fragmentation time. We aimed to evaluate the impact of this technology on patients undergoing ureteroscopy with laser lithotripsy in our hospital cohort. METHODS: We retrospectively analyzed ureteroscopy with laser lithotripsy cases performed at our hospital in 2021. All procedures performed prior to July 1, 2021 were performed with the Moses 1.0 laser, while all subsequent procedures were performed with the Moses 2.0 laser. Variables that were studied included stone density (Hounsfield units, i.e. HU), stone volume (mm3), lasing time, total energy used, stone ablation rate (volume/laser time), energy use rate (J/mm3), intraoperative stone stone-free rate, and complications. Comparisons were made between the Moses 1.0 and 2.0 groups using Student’s t tests. Multiple linear and logistic regression was also performed to evaluate the impact of energy, stone volume, stone density, and laser type on lasing time. A significance level of p-value ≤0.05 was used. RESULTS: There were 82 procedures in this cohort. Statistical results are summarized in Table 1. Overall, the only variable that reached statistical significance with Student’s t tests was the energy use rate with a p-value of 0.05. On regression analysis, the type of laser used did not have a statistically significant impact on lasing time when controlling for the total energy used, stone volume, and stone density, though the coefficient for total energy used was statistically significant with a p <0.001. CONCLUSIONS: The Moses 2.0 laser did deliver more energy per unit stone volume. However, this did not have an impact on lasing time. This remained true when controlling for total energy, stone volume, and density. It is possible that differences in lasing time will become apparent with a larger sample size and more familiarity with the 2.0 laser. Source of Funding: None © 2022 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 207Issue Supplement 5May 2022Page: e951 Advertisement Copyright & Permissions© 2022 by American Urological Association Education and Research, Inc.MetricsAuthor Information Samuel Antoine More articles by this author Kerri Thurmon More articles by this author Michael Atwell More articles by this author Xavier Glover More articles by this author Miguel Rodriguez-Homs More articles by this author Fernando Kim More articles by this author Rodrigo Donalisio da Silva More articles by this author Expand All Advertisement PDF DownloadLoading ...

MP070 - Assessment of stone ablation rates using high and low power lithotripsy with the Moses technology: An experimental study.

MP070 - Assessment of stone ablation rates using high and low power lithotripsy with the Moses technology: An experimental study.

Stone ablation rates using innovative pulse modulation technology: Vapor tunnel, virtual basket, and bubble blast. An in vitro experimental study.

Virtual BasketTM , Bubble BlastTM , and Vapor TunnelTM are three laser pulse modulation technologies that modify the holmium: yttrium-aluminum-garnet (Ho:YAG) laser pulse transmission through the creation of bubbles emerging from the fiber tip with different effects on the target stone. The primary outcome of the current study was to test the stone ablation rates for the different pulse modulation modes, Virtual Basket, Bubble Blast, and Vapor Tunnel, using different power, energy, and frequency settings. Quanta Cyber: Ho 150 WTM , a 365 µm PrecisionTM fiber, and hard and soft phantom BegoStonesTM were used in an in vitro experimental configuration in a saline bath. In the Virtual Basket mode, the combinations of power, energy and frequency were tested; 10 W = 0.5 J × 20 Hz, 10 W = 0.5 J × 20 Hz, 60 W = 1 J × 60 Hz and 60 W = 2 J × 30 Hz. In the Bubble Blast mode, the combinations, 12 W = 1.2J × 10 Hz, 60 W = 1.2J × 50 Hz and 60 W = 2 J × 30 Hz, were tested. Similarly, the combination of 10 W = 0.5 J × 20 Hz was tested with Vapor Tunnel mode. High-speed camera captures of the bubble formation and regular photographs of the fragmentation pattern were also taken for each mode. High power lithotripsy was faster and related to higher ablation rates. The Virtual Basket, Bubble Blast, and Vapor Tunnel modalities showed different ablation rates for the same energy and frequency settings. For hard stones, there was an improvement in the ablation rate using 60 W = 2 J × 30 Hz compared with 60 W = 1 J × 60 Hz and 60 W = 1.2 J × 50 Hz. The highest ablation rates were recorded using the Virtual Basket mode with the high-power settings of 2 J of energy and 30 Hz of frequency. The Virtual BasketTM pulse-modulation technology was related to the highest ablation rates for both hard and soft stones, compared to the Bubble BlastTM and the Vapor TunnelTM technologies in high-power and low-power lithotripsy respectively. For the same high power settings, higher energy seems to provide higher ablation rates.

PD54-08 HOLMIUM:YAG (HO:YAG) VERSUS THULIUM FIBER LASER (TFL) FOR TREATMENT OF UPPER URINARY TRACT CALCULI IN DUSTING MODE: A CLINICAL COMPARISON OF EFFICIENCY, EFFICACY AND COSTS EFFECTIVENESS

You have accessJournal of UrologyStone Disease: Surgical Therapy IV (PD54)1 Sep 2021PD54-08 HOLMIUM:YAG (HO:YAG) VERSUS THULIUM FIBER LASER (TFL) FOR TREATMENT OF UPPER URINARY TRACT CALCULI IN DUSTING MODE: A CLINICAL COMPARISON OF EFFICIENCY, EFFICACY AND COSTS EFFECTIVENESS Ahmed Ghazi, Mahmoud Khalil, Changyong Feng, Scott Quarrier, and Rajat Jain Ahmed GhaziAhmed Ghazi More articles by this author , Mahmoud KhalilMahmoud Khalil More articles by this author , Changyong FengChangyong Feng More articles by this author , Scott QuarrierScott Quarrier More articles by this author , and Rajat JainRajat Jain More articles by this author View All Author Informationhttps://doi.org/10.1097/JU.0000000000002081.08AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookLinked InTwitterEmail Abstract INTRODUCTION AND OBJECTIVE: Preliminary studies have demonstrated the superiority of TFL compared to Ho:YAG for dusting of urinary calculi. These are mainly based on laboratory studies with emerging clinical reports limited to optimizing TFL dusting settings. We aim to compare the efficiency, effectiveness and costs effectiveness of high power Ho:YAG (100W Empower, Olympus) to TFL (Soltive PLS, Olympus) lasers operated at a fixed dusting protocol. METHODS: A prospective study of 62 patients (31 per group) with 10–30 mm renal calculi was completed. Fixed dusting settings (0.4J X 60Hz) during retrograde intrarenal surgery (RIRS) lithotripsy was used for both lasers. Laser on time (LOT), Ablation efficacy (J/mm3) and Ablation speed (mm3/second) were calculated. Retropulsion, visibility, and bleeding during RIRS were graded by 3 urologists using 5-point Likert scales. Stone-free rate (SFR) was assessed at 1 month with non-contrast CT. Projected cost savings were calculated utilizing the formula [average LOT difference x $100/minute billed to insurance for RIRS minus $178 differential between list price of the 200m TFL ball tip and regular Ho:YAG fiber plus price differential for upgrade to PLS Soltive ($18800/1000) amortized over 1000 procedures=$18.8]. RESULTS: Mean age, BMI, stone number, density, ellipsoid stone volume and STONE score was not significantly different among both groups (Table 1). TFL lithotripsy had significantly shorter LOTs (380.6 vs 533.6 seconds, p=0.015) and higher SFRs (68% vs 34.8%, p=0.03). Both ablation efficacy (21.2 vs 12.5 J/mm3, p=0.02) and speed (4.1 vs 1.2 mm3/second, p=0.003) were significantly higher with TFL. TFL was 2.6 min faster for all stones (3.4 min for stones <15mm vs 1.7min for stones >15mm) with an overall projected $69.2 saving per case [$266- ($178+ $18.8) (Table 1). TFL was superior in terms of retropulsion (1.6 vs 2.8), visibility (1.8 vs 3.3) and bleeding (1.1 vs 1.9) gradings. CONCLUSIONS: This clinical study demonstrates TFL as a more effective, efficient and cost effective laser during RIRS lithotripsy when operated in dusting mode, producing higher stone ablation rates and speed with improved stone free rates than Ho:YAG laser. Source of Funding: None © 2021 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 206Issue Supplement 3September 2021Page: e925-e926 Advertisement Copyright & Permissions© 2021 by American Urological Association Education and Research, Inc.MetricsAuthor Information Ahmed Ghazi More articles by this author Mahmoud Khalil More articles by this author Changyong Feng More articles by this author Scott Quarrier More articles by this author Rajat Jain More articles by this author Expand All Advertisement Loading ...

Thulium fiber laser utilization in urological surgery: A narrative review

The thulium fiber laser (TFL) is a novel technology under active investigation as an conceivable alternative to the Holmium:yttrium-aluminum-garnet (Ho:YAG) laser, which is currently the gold standard for an array of urologic procedures. The purpose of this review is to discuss the existing literature on the functionality and effectiveness of TFL in urological practice. We conducted a search of the PubMed, Medline, Web of Science Core Collection, SCOPUS, Embase (OVID), and Cochrane Databases for all full articles and systematic reviews on the TFL. We found a total of 35 relevant pieces of literature. The early research findings pertaining to the TFL exhibit numerous potential advantages over the Ho:YAG laser. In vitro and ex vivo studies have highlighted the TFL's ability to utilize smaller laser fibers, obtain faster stone ablation rates, and achieve less retropulsion when tested against the Ho:YAG laser in lithotripsy. Currently, there is limited in vivo research that investigates the utilization of the TFL. The in vivo results that are available, however, look promising both for laser lithotripsy and soft tissue ablation. Indeed, the existing literature suggests that the TFL has great potential and may possess numerous technological advantages over the Ho:YAG laser, especially in laser lithotripsy. Although these early studies are promising, randomized control trials are needed to assess the full applicability of the TFL in urology.

Comparison of first-generation (1908 nm) and second-generation (1940 nm) thulium fiber lasers for ablation of kidney stones

Thulium fiber lasers (TFL) are being developed as alternatives to conventional holmium:YAG lasers for lithotripsy. TFLs emit at two primary infrared (IR) wavelengths, 1908 or 1940 nm, closely matching high (70°C) and low (22°C) temperature water absorption peaks in tissue, respectively. Water, which is present in the pores of kidney stones and fluid environment of the urinary tract as well as delivered through the working channel of the ureteroscope during lithotripsy, is a primary absorber of IR laser radiation. The water absorption peak shifts from 1940 to 1920 nm with increasing water temperature during laser ablation. At high water temperatures (70°C), the absorption coefficient is 150 cm − 1 at 1908 nm and 135 cm − 1 at 1940 nm. The goal of this study was to determine whether this 10% difference translates into a measurable difference in kidney stone ablation rates. Two TFLs (1908 and 1940 nm) were tested at similar laser parameters of 35 mJ energy/pulse, 500-μs pulse duration, 300-Hz pulse rate, and 10.5-W average power, using 200-μm-core silica optical fibers. The handheld fiber was maintained in contact with 6- to 9-mm diameter uric acid (UA) stones, immersed in a saline bath with saline flow ( n = 10 stones / group). Laser irradiation time to fragment and pass all stone fragments through a 1-mm sieve was measured and then divided into initial stone mass to calculate stone ablation rates. For each laser group (1908 and 1940 nm), initial stone mass was 270 ± 60 mg versus 260 ± 50 mg, respectively ( p = 0.9). Stone ablation rates measured 0.9 ± 0.2 and 0.9 ± 0.1 mg s − 1 ( p = 0.9). Stone ablation thresholds measured 8 ± 7 and 5 ± 13 J cm − 2 ( p = 0.8). There was no significant difference in UA stone ablation thresholds and ablation rates between 1908- and 1940-nm wavelengths. Newer, more compact, efficient, and higher peak power TFLs operating at 1940 nm provide comparable stone ablation rates to older 1908-nm TFLs for similar laser parameters.

Miniature ball-tip optical fibers for use in thulium fiber laser ablation of kidney stones.

Optical fibers, consisting of 240-μm-core trunk fibers with rounded, 450-μm-diameter ball tips, are currently used during Holmium:YAG laser lithotripsy to reduce mechanical damage to the inner lining of the ureteroscope working channel during fiber insertion and prolong ureteroscope lifetime. Similarly, this study tests a smaller, 100-μm-core fiber with 300-μm-diameter ball tip during thulium fiber laser (TFL) lithotripsy. TFL was operated at a wavelength of 1908 nm, with 35-mJ pulse energy, 500-μs pulse duration, and 300-Hz pulse rate. Calcium oxalate/phosphate stone samples were weighed, laser procedure times were measured, and ablation rates were calculated for ball tip fibers, with comparison to bare tip fibers. Photographs of ball tips were taken before and after each procedure to track ball tip degradation and determine number of procedures completed before need for replacement. A high speed camera also recorded the cavitation bubble dynamics during TFL lithotripsy. Additionally, saline irrigation rates and ureteroscope deflection were measured with and without the presence of TFL fiber. There was no statistical difference (P>0.05) between stone ablation rates for single-use ball tip fiber (1.3±0.4 mg/s) (n=10), multiple-use ball tip fiber (1.3±0.5 mg/s) (n=44), and conventional single-use bare tip fibers (1.3±0.2 mg/s) (n=10). Ball tip durability varied widely, but fibers averaged greater than four stone procedures before failure, defined by rapid decline in stone ablation rates. Mechanical damage at the front surface of the ball tip was the limiting factor in fiber lifetime. The small fiber diameter did not significantly impact ureteroscope deflection or saline flow rates. The miniature ball tip fiber may provide a cost-effective design for safe fiber insertion through the ureteroscope working channel and into the ureter without risk of instrument damage or tissue perforation, and without compromising stone ablation efficiency during TFL lithotripsy.

A Miniaturized, 1.9F Integrated Optical Fiber and Stone Basket for Use in Thulium Fiber Laser Lithotripsy.

The thulium fiber laser (TFL) is being explored as an alternative laser lithotripter to the standard holmium:yttrium-aluminum-garnet laser. The more uniform beam profile of the TFL enables higher power transmission through smaller fibers. In this study, a 100-μm core, 140-μm outer-diameter (OD) silica fiber with 5-mm length hollow steel tip was integrated with 1.3F (0.433-mm OD) nitinol wire basket to form a 1.9F (0.633-mm OD) device. TFL energy of 30 mJ, 500 μs pulse duration, and 500 Hz pulse rate was delivered to human uric acid stones, ex vivo. Stone ablation rates measured 1.5 ± 0.2 mg/s, comparable to 1.7 ± 0.3 mg/s using bare fiber tips separately with stone basket. With further development, this device may minimize stone retropulsion, allowing more efficient TFL lithotripsy at higher pulse rates. It may also provide increased flexibility, higher saline irrigation rates through the ureteroscope working channel, reduce fiber degradation compared with separate fiber and basket manipulation, and reduce laser-induced nitinol wire damage.

Rapid Thulium Fiber Laser Lithotripsy at Pulse Rates up to 500 Hz Using a Stone Basket

Our laboratory is currently studying the experimental thulium fiber laser (TFL) for ablation of kidney stones. Previous studies have reported increased stone ablation rates with TFL operation at higher pulse rates; however, stone retropulsion remains an obstacle to more efficient stone ablation. This study explores TFL operation at high pulse rates in combination with a stone stabilization device (e.g., stone basket) for improved stone ablation efficiency. A TFL beam with pulse energy of 35 mJ, pulse duration of 500 μs, and pulse rates of 10-500 Hz was delivered through 100-μm-core, low-OH, silica fibers, in contact mode with human uric acid (UA) and calcium oxalate monohydrate (COM) stones, ex vivo. TFL operation at 500 Hz produced mean UA and COM stone ablation rates up to 4.4 and 1.4 mg/s, respectively. High TFL pulse rates produce increased stone ablation rates that may be suitable for future translation into the clinic.

Thulium fiber laser ablation of kidney stones using a 50-μm-core silica optical fiber

Our laboratory is currently studying the experimental thulium fiber laser (TFL) as a potential alternative laser lithotripter to the gold standard, clinical Holmium:YAG laser. We have previously demonstrated the efficient coupling of TFL energy into fibers as small as 100-μm-core-diameter without damage to the proximal end. Although smaller fibers have a greater tendency to degrade at the distal tip during lithotripsy, fiber diameters (≤200 μm) have been shown to increase the saline irrigation rates through the working channel of a flexible ureteroscope, to maximize the ureteroscope deflection, and to reduce the stone retropulsion during laser lithotripsy. In this study, a 50-μm-core-diameter, 85-μm-outer-diameter, low-OH silica fiber is characterized for TFL ablation of human calcium oxalate monohydrate urinary stones, ex vivo. The 50-μm-core fiber consumes approximately 30 times less cross-sectional area inside the single working channel of a ureteroscope than the standard 270-μm-core fiber currently used in the clinic. The ureteroscope working channel flow rate, including the 50-μm fiber, decreased by only 10% with no impairment of ureteroscope deflection. The fiber delivered up to 15.4±5.9 W under extreme bending (5-mm-radius) conditions. The stone ablation rate measured 70±22 μg/s for 35-mJ-pulse-energy, 500-μs-pulse-duration, and 50-Hz-pulse-rate. Stone retropulsion and fiber burnback averaged 201±336 and 3000±2600 μm, respectively, after 2 min. With further development, thulium fiber laser lithotripsy using ultra-small, 50-μm-core fibers may introduce new integration and miniaturization possibilities and potentially provide an alternative to conventional Holmium:YAG laser lithotripsy using larger fibers.

Hollow steel tips for reducing distal fiber burn-back during thulium fiber laser lithotripsy

The use of thulium fiber laser (TFL) as a potential alternative laser lithotripter to the clinical holmium:YAG laser is being studied. The TFL's Gaussian spatial beam profile provides efficient coupling of higher laser power into smaller core fibers without proximal fiber tip degradation. Smaller fiber diameters are more desirable, because they free up space in the single working channel of the ureteroscope for increased saline irrigation rates and allow maximum ureteroscope deflection. However, distal fiber tip degradation and "burn-back" increase as fiber diameter decreases due to both excessive temperatures and mechanical stress experienced during stone ablation. To eliminate fiber tip burn-back, the distal tip of a 150-μm core silica fiber was glued inside 1-cm-long steel tubing with fiber tip recessed 100, 250, 500, 1000, or 2000 μm inside the steel tubing to create the hollow-tip fiber. TFL pulse energy of 34 mJ with 500-μs pulse duration and 150-Hz pulse rate was delivered through the hollow-tip fibers in contact with human calcium oxalate monohydrate urinary stones during ex vivo studies. Significant fiber tip burn-back and degradation was observed for bare 150-μm core-diameter fibers. However, hollow steel tip fibers experienced minimal fiber burn-back without compromising stone ablation rates. A simple, robust, compact, and inexpensive hollow fiber tip design was characterized for minimizing distal fiber burn-back during the TFL lithotripsy. Although an increase in stone retropulsion was observed, potential integration of the hollow fiber tip into a stone basket may provide rapid stone vaporization, while minimizing retropulsion.