Comparison of holmium:yttrium-aluminium-garnet (YAG), thulium fiber laser, and pulsed thulium:YAG lasers on soft tissue: an ex vivo study.

OBJECTIVES: To assess laser-tissue interactions through ablation, coagulation, and carbonisation characteristics in a non-perfused porcine kidney model between three pulsed lasers: holmium (Ho): yttrium-aluminium-garnet (YAG), thulium fiber laser (TFL), and pulsed thulium (p-Tm):YAG. MATERIALS AND METHODS: A 150-W Ho:YAG, a 60-W TFL, and a 100-W p-Tm:YAG lasers were compared. The laser settings that can be set identically between the three lasers and be clinically relevant for prostate laser enucleation were identified and used on fresh, unfrozen porcine kidneys. Laser incisions were performed using stripped laser fibers of 365 and 550 µm, set at distances of 0 and 1 mm from the tissue surface at a constant speed of 2 mm/s. Histological analysis evaluated shape, depth, width of the incision, axial coagulation depth, and presence of carbonisation. RESULTS: Incision depths, widths, and coagulation zones were greater with Ho:YAG and p-Tm:YAG lasers than TFL. Although no carbonisation was found with the Ho:YAG and p-Tm:YAG lasers, it was common with TFL, especially at high frequencies. The shapes of the incisions and coagulation zones were more regular and homogeneous with the p-Tm:YAG laser and TFL than with Ho:YAG laser. Regardless of the laser used, short pulse durations resulted in deeper incisions than long pulse durations. Concerning the distance, we found that to be effective, TFL had to be used in contact with the tissue. Finally, 365-µm fibers resulted in deeper incisions, while 550-µm fibers led to wider incisions and larger coagulation zones. CONCLUSION: Histological analysis revealed greater tissue penetration with the p-Tm:YAG laser compared to the TFL, while remaining less than with Ho:YAG. Its coagulation properties seem interesting insofar as it provides homogeneous coagulation without carbonisation, while incisions remained uniform without tissue laceration. Thus, the p-Tm:YAG laser appears to be an effective alternative to Ho:YAG and TFL lasers in prostate surgery.

How much energy do we need to ablate 1 cubic millimeter of stone during Thulium Fiber Laser lithotripsy? An in vitro study.

INTRODUCTION: Both Holmium:yttrium-aluminium-garnet (Ho:YAG) laser and Thulium Fiber Laser (TFL) can effectively treat all urinary stone types. This in vitro study evaluated the ablation volume per pulse (AVP) and required energy needed to ablate 1mm3 (RE, J/mm3) of various stone types at different laser settings with TFL. METHODS: 272-µm core-diameter laser fibers (Boston Scientific©) were connected to a 50 Watts TFL generator (IPG®). An experimental setup immerged human stones of calcium oxalate monohydrate (COM), uric acid (UA), and cystine (CYS) with a single pulse lasing emission (0.5/0.8/1 J), in contact mode. Stones were dried out before three-dimensional scanning to measure AVP and deduce from the pulse energy (PE) and AVP the RE. A direct comparison with known Ho:YAG's AVP and RE was then carried out. RESULTS: AVP for COM stones was significantly greater than those for CYS stones and similar to UA stones (p = 0.02 and p = 0.06, respectively). If AVP increased with PE against COM and UA stones, AVP decreased against CYS stones. 1 J PE resulted in a threefold lower RE compared with other PE for COM stones. On the contrary, RE for CYS increased with PE, whereas PE did not had influence on RE for UA. TFL was associated with greater AVP for COM, but lower for UA and CYS stones compared to Ho:YAG laser. CONCLUSION: This in vitro study firstly describes the ablation volume per pulse and required energy to treat a cubic millimeter of three frequent human stone types, and suggest TFL could not be suited for cystine. Therefore, stone composition could be considered when choosing the laser source for lithotripsy.

Is "Kidney Stone Calculator" efficient in predicting ureteroscopic lithotripsy duration? A holmium:YAG and thulium fiber lasers comparative analysis.

PURPOSE: This study aimed to evaluate the ability of Kidney Stone Calculator (KSC), a flexible ureteroscopy surgical planning software, to predict the lithotripsy duration with both holmium:YAG (Ho:YAG) and thulium fiber laser (TFL). METHODS: A multicenter prospective study was conducted from January 2020 to April 2023. Patients with kidney or ureteral stones confirmed at non-contrast computed tomography and treated by flexible ureteroscopy with laser lithotripsy were enrolled. "Kidney Stone Calculator" provided stone volume and subsequent lithotripsy duration estimation using three-dimensional segmentation of the stone on computed tomography and the graphical user interface for laser settings. The primary endpoint was the quantitative and qualitative comparison between estimated and effective lithotripsy durations. Secondary endpoints included subgroup analysis (Ho:YAG-TFL) of differences between estimated and effective lithotripsy durations and intraoperative outcomes. Multivariate analysis assessed the association between pre- and intraoperative variables and these differences according to laser source. RESULTS: 89 patients were included in this study, 43 and 46 in Ho:YAG and TFL groups, respectively. No significant difference was found between estimated and effective lithotripsy durations (27.37 vs 28.36 min, p = 0.43) with a significant correlation (r = + 0.89, p < 0.001). Among groups, this difference did not differ (p = 0.68 and 0.07, respectively), with a higher correlation between estimated and effective lithotripsy durations for TFL compared to Ho:YAG (r = + 0.95, p < 0.001 vs r = + 0.81, p < 0.001, respectively). At multivariate analysis, the difference was correlated with preoperative (volume > 2000 mm3 (Ho:YAG), 500-750 mm3 SV and calyceal diverticulum (TFL)), operative (fragmentation setting (p > 0.001), and basket utilization (p = 0.05) (Ho:YAG)) variables. CONCLUSION: KSC is a reliable tool for predicting the lithotripsy duration estimation during flexible ureteroscopy for both Ho:YAG and TFL. However, some variables not including laser source may lead to underestimating this estimation.

Development and optimization of Laser Shock Repeated Dense Peening (LSRDP) using most advanced laser architectures.

The laser shock peening process (LSP), used to reinforce metals, currently has two major configurations with limitations. (1) Laser irradiation with large spot sizes, but with the need to use a thermal protective coating to avoid detrimental thermal damage (which increases the overall cost of the process) or (2) laser irradiation without thermal coating but with very small spot sizes and high overlap ratios, thus increasing the amount of time required to treat a given surface. In this study, we develop a new faster configuration for the LSP process, which can be applied without a thermal coating, but is still effective regarding surface treatment time. A new laser system has been developed for this faster configuration and has been used to perform the LSP treatment of aluminum alloys at a high-repetition rate. This new DPSS Q-switched Nd:YAG laser, delivers 1 J of energy with a pulse duration from 7 to 21 ns at a very high frequency of 200 Hz. We also studied the laser/matter interaction, according to the laser pulse duration, energy, and its wavelength. The water confinement (ejection and renewing) was monitored while an air-blowing system was implemented to manage water issues identified with this new configuration. Altogether, we demonstrated that such a configuration is fully operational.

Comparison of the ablation rates, fissures and fragments produced with 150 µm and 272 µm laser fibers with superpulsed thulium fiber laser: an in vitro study.

INTRODUCTION: Holmium:YAG(Ho:YAG) is currently the standard for lithotripsy. Superpulsed Thulium Fiber Laser(TFL) has been evaluated as an alternative for lithotripsy, using laser fibers with core-diameters(CDF) down to 50 µm and additional available settings suitable for "dusting" technique. This in-vitro study compared ablation rates, fissures and fragments' size with 150µmCDF or 272µmCDF with different laser settings using TFL and Ho:YAG. METHODS: 150CDF and 272CDF were compared using three settings for TFL "fine dusting"(FD:0.15 J/100 Hz); "dusting"(D:0.5 J/30 Hz); "fragmentation"(Fr:1 J/15 Hz) and Ho:YAG(D and Fr). An experimental setup consisting of immerged 10 mm cubes of artificial hard(H) or soft(S) stone phantoms was used with a 20 s' lasing time and a spiral trajectory, in contact mode. Fragments (acquired through sieves) and stones were observed under optical microscopy before three-dimensional scanning to measure fragments and fissures(DOF) mean diameters and ablation volumes. RESULTS: Ablation volumes in with 150CDF-TFL and 272CDF-TFL were higher than those for 272CDF-Ho:YAG in both "dusting" (twofold and threefold) and "fragmentation"(1,5-fold and twofold). "Fine dusting" ablation rates with 150CDF-TFL and 272CDF-TFL were respectively at least 1,5-fold and twofold higher than those for 272CDF-Ho:YAG in "dusting". 150CDF produced significantly smaller DOF than 272CDF in all settings against S and H except in fragmentation. 150CDF produced lower fragments' diameter than 272CDF in all settings except dusting. CONCLUSION: These preliminary studies demonstrate that at equal settings and CDF, TFL ablation rates are at least two-fold higher than those with Ho:YAG. 150CDF produces smaller fissures and fragments (that meets the definition of "dusting" lithotripsy) than 272CDF and higher ablation volumes than Ho:YAG.

Evaluation of a free 3D software for kidney stones' surgical planning: "kidney stone calculator" a pilot study.

INTRODUCTION: Kidney Stone Calculator (KSC) is a free, three-dimensional (3D) planning software for flexible ureteroscopy(fURS) with Holmium:YAG(Ho:YAG) endocorporeal lithotripsy (EL). KSC provides the stone volume (SV) and expected duration of lithotripsy (ExDL) estimations based on non-enhanced-CT scan (NECT) DICOM series. We aimed to provide a preclinical and clinical evaluation of KSC. PATIENTS AND METHODS: A preclinical evaluation measured the SV by three operators (resident, endourology expert and research engineer) among 17 NECT cases. Between January and March 2020, a multicentric, prospective, observational double-blind clinical evaluation was conducted in patients presenting with renal stones treated with Ho:YAG-EL during fURS and preoperative NECT. Demographic and surgical data were collected. The primary endpoint was a significant median difference between ExDL and EffectiveDL (EfDL). Second, efficiency (J/mm3) and efficacy (mm3/min) ratios were calculated. RESULTS: The preclinical evaluation showed no significant difference in the SV measurements among operators (p > 0.05). Pearson and Kendall coefficients of 0.99 and 0.98, respectively, were found. Twenty-six patients were included in the clinical evaluation, with a median age of 55 years. In 66% of cases, there was a single stone located in the lower pole, with a density > 1000 Hounsfield Unit observed in 42% and 85% of cases. A 14% [Q1-Q3 (5.4-24.8); p = 0.36] median difference between ExDL and EfDL was noted, which was greater in the case of lower pole stones with no possible relocation (p = 0.008). Median values of 17.6 J/mm3 and 0.4 (0.32-0.56) mm3/s EL were also noted. CONCLUSIONS: Kidney Stone Calculator is a reproducible and accurate software that allows for an estimation of the stone burden and provides an ExDL for URSf. Defining the influencing factors of EL will improve its ExDL.

How much energy do we need to ablate 1 mm3 of stone during Ho:YAG laser lithotripsy? An in vitro study.

INTRODUCTION: Holmium:yttrium-aluminium-garnet (Ho:YAG) is currently the gold standard for lithotripsy for the treatment of all known urinary stone types. Stone composition and volume are major determinants of the lithotripsy. This in vitro study evaluated the required energy to ablate 1 mm3 of various stone types with different laser settings using Ho:YAG. METHODS: 272 µm core-diameter laser fibers (Boston Scientific©) were connected to a 30 Watt MH1 Ho:YAG generator (Rocamed®). An experimental setup consisting of immerged human stones of calcium oxalate monohydrate (COM), uric acid (UA) or cystine (Cys) was used with a single pulse lasing emission (0.6/0.8/1 J), in contact mode. Stones were dried out before three-dimensional scanning to measure ablation volume per pulse (AVP) and required energy to treat 1 mm3 (RE). RESULTS: All settings considered, ablation volumes per pulse (AVP) for COM were significantly lower than those for UA and Cys (p = 0.002 and p = 0.03, respectively), whereas AVP for Cys was significantly lower than those for UA (p = 0.03). The mean REs at 0.6 J pulse energy (PE) for COM, Cys and UA were 34, 8.5 and 3.2 J, respectively The mean REs at 1 J PE for COM, Cys and UA were 14.7, 6.4 and 2 J, respectively. At 0.6 J PE, RE for COM was more than tenfold and fivefold higher than those for UA and Cys, respectively. CONCLUSION: This in vitro study shows for the first time a volumetric evaluation of Ho:YAG efficiency by the ablation volume per pulse on human stone samples, according to various pulse energies. The REs for COM, UA and Cys should be considered in clinical practice.

Ho:YAG laser lithotripsy in non-contact mode: optimization of fiber to stone working distance to improve ablation efficiency.

PURPOSE: To evaluate how variable working distances between the laser fiber and the stone influence ablation volume. METHODS: A laser fiber was fixed on a robotic arm perpendicular to an artificial stone. A single laser pulse was triggered at different working distances (0-2.0 mm in 0.2 mm increments) between the distal fiber tip and the stone. To achieve a measurable impact, pulse energy was set to 2 and 3 J, with either short or long pulse duration. Ablation volume was calculated with an optical microscope. Experiments were repeated five times for each setting. RESULTS: Highest ablation volume was observed with a long pulse of 3 J at a working distance of 0.4 mm between the laser fiber and the stone surface (p value < 0.05). At 2 J, the highest ablation volume was noticed with a short pulse in contact mode. However, ablation volume of the latter was not significantly greater than with a long pulse of 2 J at a working distance of 0.4 mm (p value > 0.05). Compared to lithotripsy in contact mode, triggering a single long pulse at 0.4 mm increased ablation volume by 81% (p value = 0.016) at 2 J and by 89% (p value = 0.034) at 3 J. CONCLUSIONS: For Ho:YAG laser lithotripsy, ablation volume may be higher in non-contact mode using long pulses, rather than in direct contact to the stone. Findings of the current study support the need of further studies of lithotripsy in non-contact mode.

In Vitro Comparison of Pulsed-Thulium:YAG, Holmium:YAG, and Thulium Fiber Laser.

Objective: To characterize the pulse characteristics and risk of fiber fracture (ROF) of the pulsed-Thulium:YAG (p-Tm:YAG) laser and to compare its ablation volumes (AVs) against Holmium:Yttrium-Aluminium-Garnet (Ho:YAG) laser and Thulium fiber laser (TFL). Materials and Methods: p-Tm:YAG (100 W-Thulio, Dornier-Medtech©, Germany) was characterized using single-use 272 µm core-diameter-fibers. p-Tm:YAG characterization included pulse shape, duration, and peak power (PP) studies. ROF was assessed after 5 minutes of continuous laser activation (CLA) at five decreasing fiber bend radii (1, 0.9, 0.75, 0.6, and 0.45 cm). p-Tm:YAG, Ho:YAG (120 W-Cyber-Ho, Quanta®, USA), and TFL (60 W-TFLDrive, Coloplast®, Denmark) AVs were compared using a 20-mm linear CLA at 2 mm/second velocity in contact with 20 mm3 hard stone phantoms (HSP) and soft stone phantoms (SSP) (15:3 and 15:5 water to powder ratio, respectively) fully submerged in saline at 0.5 J-20 Hz or 1 J-10 Hz. After CLA, phantoms underwent three-dimensional (3D) micro-scanning (CT) and subsequent 3D segmentation to estimate the AVs, using 3DSlicer©. Each experiment was performed in triplicate. Results: p-Tm:YAG presents a uniform pulse profile in all of the available preset modes. PP ranged from 564 to 2199 W depending on pulse mode. No laser fiber fracture occurred at any bend radius. p-Tm:YAG achieved similar mean AVs to TFL and Ho:YAG for HSP (8.96 ± 3.1 vs 9.78 ± 1.1 vs 8.8 ± 2.8 mm3, p = 0.67) but TFL was associated with higher AVs compared with p-Tm:YAG and Ho:YAG (12.86 ± 1.85 vs 10.12 ± 1.89 vs 7.56 ± 2.21 mm3, p = 0.002) against SSP. AVs for HSP increased with pulse energy for p-Tm:YAG and Ho:YAG and (11.56 ± 1.8 vs 6.36 ± 0.84 mm3 and 11.27 ± 1.98 vs 6.34 ± 0.55 mm3, p = 0.03 and p = 0.02), whereas AVs for SSP were similar across laser settings for all laser sources. AVs with TFL were similar across laser settings for both phantom types. Conclusion: p-Tm:YAG combines intermediate PP between Ho:YAG and TFL, a uniform pulse profile, no ROF with increasing deflection and effective ablation rates. Further clinical studies are needed to confirm these in vitro results.

Comparison of Holmium:YAG and Thulium Fiber Lasers on Soft Tissue: An Ex Vivo Study.

Objective: To assess the fiber-tissue interaction through ablation, coagulation, and carbonization characteristics of the Ho:YAG laser and super pulsed thulium fiber laser (TFL) in a nonperfused porcine kidney model. To assess the degradation of laser fibers during soft tissue treatment. Methods: A 50 W TFL generator was compared with a 120 W Ho:YAG laser. The laser settings that can be set identically between the two lasers (pulse energy and frequency), and clinically relevant for prostate laser enucleation, were identified and used for tissue incisions on fresh nonfrozen porcine kidneys. For each parameter, the short, medium, and long pulse durations for the Ho:YAG generator and the different peak powers 150, 250, and 500 W for the TFL generator were also tested. Laser incisions were performed with 550 µm stripped laser fiber fixed on a robotic arm at a distance of 0.1 mm with the tissue surface and at a constant speed of 10 mm/s. Histologic analysis was then performed, evaluating incision shape, incision depth and width, axial coagulation depth, and presence of carbonization. Degradation of the laser fiber was defined as reduction of laser fiber tip length after laser activation. Results: Incision depths and areas of coagulation were greater with the Ho:YAG laser than those with the TFL. Although no carbonization zone was found with the Ho:YAG laser, this was constant with the TFL. Although a fiber tip degradation was constantly observed with Ho:YAG laser, except in the case of a long pulse duration and low pulse energy (0.2 J), this was not the case with TFL. Conclusion: TFL appears to be an efficient alternative to Ho:YAG laser for soft tissue surgery. The histologic analysis found greater tissue penetration with the Ho:YAG laser and different coagulation properties between the two lasers. These results need to be investigated in vivo to assess the clinical impact of these differences and find the optimal settings for laser prostate enucleation.

Assessment of Factors Involved in Laser Fiber Degradation with Thulium Fiber Laser.

Objectives: To assess the effect of various factors on laser fiber tip degradation with the thulium fiber laser (Tm-fiber): fiber stripping, adjustable laser settings (energy, frequency, peak power), and stone density. Methods: Two hundred seventy-three micrometer fibers were used with a 50W Tm-fiber. First, we assessed the evolution of power transmission with stripped and unstripped fibers submerged in saline. The laser was continuously activated for 5 minutes. The influence of each laser parameter (energy, frequency, and peak power) on fiber degradation was assessed by loss of power transmission and reduction of tip length. Second, we assessed the evolution of power transmission after 150 seconds of lithotripsy in a quasicontact mode against soft and hard BegoStones. The influence of lithotripsy with different laser settings on fiber degradation was assessed by loss of power transmission. Results: Power transmission was close to 100% with stripped fibers, while a power gain appeared for unstripped fibers after 5 minutes of laser emission. Thus, only stripped laser fibers were used during the second series of experiments. Regardless of laser settings, there was a constant loss of measured power transmission after lithotripsy with a significant difference between soft and hard stones, p < 0.0001. Power transmission was 67% and 78% against hard and soft stones, respectively. While there was no influence of peak power on power output against hard stones, there was a significant one against soft stones. Conclusions: The main determinant of loss of power transmission during lithotripsy in contact mode with Tm-fiber is the stone density. Higher loss of power transmission occurs against hard stones than soft stones. All peak powers may be used against hard stones without a difference, while high peak power appears as an additional factor of power loss against soft stones, but this decrease will not the reach the one obtained with hard stones.

Laser-Induced Ocular Lesions with Thulium Fiber Laser in Endourology: An Ex Vivo Study.

Introduction and Objectives: The thulium fiber (Tm-F) laser is currently studied as an alternative to the holmium: yttrium-aluminum-garnet (Ho:YAG) laser, the gold standard for endocorporeal laser lithotripsy. We aimed to evaluate the ex vivo effects of an accidental Tm-F laser exposure on bovine eyes and to test the protective action of different eyeglasses in preventing eye lesions in case of an accident. Methods: A 50-W TFL generator (IPG Photonics®, Russia) with a wavelength of 1940 nm and 200-µm core diameter fibers (CDFs) were used. The laser fiber tip was pointed perpendicularly at different distances (0, 1, 3, 5, 8, and 10 cm, respectively) to the pupil center of the bovine eye. The Tm-F laser was activated for 1 or 3 seconds at three different settings (0.5 J-20 Hz, 1 J-10 Hz, and 2 J-10 Hz, respectively). The experiment was repeated using laser safety glasses and eyeglasses. After lasering, eye samples were immersed in a 0.5% fluorescein serum (Faure-Ciba-Geigy®, Switzerland), then rinsed with saline. White and blue light examination looked for localized epithelial burns (LEBs), extended epithelial burns (EEBs), superficial corneal ulcerations (SCUs), and deep corneal ulcerations (DCUs). Results: A total of 68 bovine eyes were used. Despite the laser settings, both DCU (contact) and SCU (1 cm) developed without eye protection for 1 and 3 seconds of lasering. At the 3-cm fiber-eye distance, only burning lesions were observed. Over 5 cm, no lesion was found. At contact or 1-cm fiber-eye distance, pulse energy did not change the lesion grade, but at 3 cm, high pulse energy led to higher grade corneal lesions (0.5 J-10 Hz:LEB; 1 J-10 Hz:EEB). Despite the fiber-eye distance, no corneal lesions were reported in the laser safety glass or eyeglass group for 1 second of laser exposure. Conclusions: Our study highlights the risk of eye damage caused by Tm-F. Without proper eye protection, the Tm-F laser can cause corneal lesions up to 5 cm in distance with 1 second of exposure despite laser settings. Only dedicated protective eyeglasses are effective for long exposures.

Impact of Laser Fiber Diameter and Irrigation Fluids on Induced Bubble Stream Dynamics with Thulium Fiber Laser: An In Vitro Study.

Objectives: The Thulium Fiber Laser (TFL) is studied as an alternative to the holmium:yttrium-aluminium-garnet (Ho:YAG) laser for lithotripsy, with the advantage of an induced bubble stream (IBS). This in vitro study compared the TFL's IBS with 150- and 272 µm-core-diameter laser fiber (CDF) and in four irrigant fluids. Methods: A TFL of 50 W (IPG Photonics©) and 150 and 272 µm-CDF (Boston Scientific©) were used, comparing nine energies (in the range from 0.025 to 4 J). An experimental setup consisted of a vertically disposed fiber in a cuvette filled with saline, iodinated contrast agent (IOA), human urine, or deionized water (DW) at ambient temperature. High-speed imaging of three consecutive IBS was performed to determine the influence of energy on their maximum length (ML; µm), width (MW; µm), and duration (MD; µs). Fibers were cleaved with ceramic scissors between each experience. Results: The IBS had higher ML and MW and MD with 150CDF than 272CDF. Maximum pulse rate for 150CDF and 272CDF was 2182 and 2000 Hz, respectively. Every maximum power was higher than the technological limit of TFL (>50 W). At equal energy density, 150CDF was associated with lower dimensions and durations. The IBS had higher maximum dimensions in IOA compared with saline solution (SS). Compared with DW and urine, IBS in IOA were longer beyond 500 mJ. Over 25 mJ, IBS were thinner in DW, urine, and SS. The IBS in DW, urine, and SS had similar maximum dimensions. The IBS's duration was higher in IOA compared with DW, urine, and SS, meaning a lower theoretical maximum pulse rate and power in IOA. Conclusion: Lasering with 150CDF fits with lower pulse energies-higher pulse rates settings than 272CDF, such as fine dusting mode. In IOA, Induced Bubbles Streams present higher dimensions and durations than in other studied fluids, related to its higher viscosity. Safety distance and pulse rate should be increased and decreased, respectively.

Comparison of Holmium:YAG and Thulium Fiber Lasers on the Risk of Laser Fiber Fracture.

OBJECTIVES: To compare the risk of laser fiber fracture between Ho:YAG laser and Thulium Fiber Laser (TFL) with different laser fiber diameters, laser settings, and fiber bending radii. METHODS: Lengths of 200, 272, and 365 µm single use fibers were used with a 30 W Ho:YAG laser and a 50 W Super Pulsed TFL. Laser fibers of 150 µm length were also tested with the TFL only. Five different increasingly smaller bend radii were tested: 1, 0.9, 0.75, 0.6, and 0.45 cm. A total of 13 different laser settings were tested for the Ho:YAG laser: six fragmentation settings with a short pulse duration, and seven dusting settings with a long pulse duration. A total of 33 different laser settings were tested for the TFL. Three laser settings were common two both lasers: 0.5 J × 12 Hz, 0.8 J × 8 Hz, 2 J × 3 Hz. The laser was activated for 5 min or until fiber fracture. Each measurement was performed ten times. RESULTS: While fiber failures occurred with all fiber diameters with Ho:YAG laser, none were reported with TFL. Identified risk factors of fiber fracture with the Ho:YAG laser were short pulse and high energy for the 365 µm fibers (p = 0.041), but not for the 200 and 272 µm fibers (p = 1 and p = 0.43, respectively). High frequency was not a risk factor of fiber fracture. Fiber diameter also seemed to be a risk factor of fracture. The 200 µm fibers broke more frequently than the 272 and 365 µm ones (p = 0.039). There was a trend for a higher number of fractures with the 365 µm fibers compared to the 272 µm ones, these occurring at a larger bend radius, but this difference was not significant. CONCLUSION: TFL appears to be a safer laser regarding the risk of fiber fracture than Ho:YAG when used with fibers in a deflected position.

Laser Fiber Displacement Velocity during Tm-Fiber and Ho:YAG Laser Lithotripsy: Introducing the Concept of Optimal Displacement Velocity.

BACKGROUND: Endocorporeal laser lithotripsy (EL) during flexible ureteroscopy (URS-f) often uses "dusting" settings with "painting" technique. The displacement velocity of the laser fiber (LF) at the stone surface remains unknown and could improve EL's ablation rates. This in vitro study aimed to define the optimal displacement velocity (ODV) for both holmium:yttrium-aluminium-garnet (Ho:YAG) and thulium fiber laser (Tm-Fiber). METHODS: A 50W-TFL (IRE Polus®, Moscow, Russia) and a 30W-MH1-Ho:YAG laser (Rocamed®, Signes, Provence-Alpes-Côte d'Azur, France), were used with 272 µm-Core-Diameter LF (Sureflex, Boston Scientific©, San Jose, CA, USA), comparing three TFL modes, "fine dusting" (FD: 0.05-0.15 J/100-600 Hz); "dusting" (D: 0.5 J/30-60 Hz); "fragmentation" (Fr: 1 J/15-30 Hz) and two Ho:YAG modes (D: 0.5 J/20 Hz, Fr: 1 J/15 Hz). An experimental setup consisting of immerged cubes of calcium oxalate monohydrate (COM) stone phantoms (Begostone Plus, Bego©, Lincoln, RI, USA) was used with a 2 s' laser operation time. LF were in contact with the stones, static or with a displacement of 5, 10 or 20 mm. Experiments were repeated four times. Stones were dried and µ-scanned. Ablation volumes (mm3) were measured by 3D-segmentation. RESULTS: ODV was higher in dusting compared to fragmentation mode during Ho:YAG lithotripsy (10 mm/s vs. 5 mm/s, respectively). With Tm-Fiber, dusting and fragmentation OVDs were similar (5 mm/s). Tm-Fiber ODV was lower than Ho:YAGs in dusting settings (5 mm/s vs. 10 mm/s, respectively). Without LF displacement, ablation volumes were at least two-fold higher with Tm-Fiber compared to Ho:YAG. Despite the LF-DV, we report a 1.5 to 5-fold higher ablation volume with Tm-Fiber compared to Ho:YAG. CONCLUSIONS: In dusting mode, the ODVTm-Fiber is lower compared to ODVHo:YAG, translating to a potential easier Tm-Fiber utilization for "painting" dusting technique. The ODV determinants remain unknown. Dynamic ablation volumes are higher to static ones, regardless of the laser source, settings or LF displacement velocity.

The True Ablation Effect of Holmium YAG Laser on Soft Tissue.

PURPOSE: The holmium YAG (Ho:YAG) laser penetration depth (PD) of 0.4 mm has been widely described. Nonetheless, in physics, this concept refers to the tissue thickness at which 90% of the energy has been absorbed and not to the incision depth (ID) that the laser can achieve in tissue. The aim of this study is to evaluate the ablation efficiency of Ho:YAG laser on soft tissue. MATERIALS AND METHODS: With an automated robotic arm, systematic fissures were performed on flat veal kidney specimens. Broad setting spectrums from 2.5 to 80 W, short and long pulse, were tested with 272 and 365 µm laser fibers. Experiments were repeated three times. Two pathologists in a blinded manner measured the width, depth, and coagulation area with electronic microscopy. RESULTS: The overall mean ID was 2 mm (0.25-4.39) and the mean width was 1 mm (0.3-3.1). The mean coagulation thickness was 0.48 mm (0.25-1.73). The higher the frequency and energy, the deeper and wider was the incision p < 0.001. No differences were observed regarding the fiber diameter. The pulse length did not affect the ID, although the mean width was greater with short pulse p = 0.04. The outer mean coagulation was increased by increasing energy but not by increasing frequency p > 0.119. CONCLUSIONS: The overall mean ID was significantly higher than the theoretical 0.4 mm PD described for Ho:YAG laser. The energy, frequency, and pulse length had individual effects regarding ID, incision width, and coagulation. The ID should be specified in accordance with the laser's power output and should not be confused with the physics of PD concept.

Impact of the Curve Diameter and Laser Settings on Laser Fiber Fracture.

OBJECTIVE: To analyze the risk factors for laser fiber fractures when deflected to form a curve, including laser settings, size of the laser fiber, and the fiber bending diameter. MATERIALS AND METHODS: Single-use 272 and 365 µm fibers (Rocamed®, Monaco) were employed along with a holmium laser (Rocamed). Five different fiber curve diameters were tested: 9, 12, 15, 18, and 20 mm. Fragmentation and dusting settings were used at a theoretical power of 7.5 W. The laser was activated for 5 minutes and the principal judgment criterion was fiber fracture. Every test for each parameter, bending diameter, and fiber size combinations was repeated 10 times. RESULTS: With dusting settings, fibers broke more frequently at a curved diameter of 9 mm for both 272 and 365 µm fibers (p = 0.037 and 0.006, respectively). Using fragmentation settings, fibers broke more frequently at 12 mm for 272 µm and 15 mm for 365 µm (p = 0.007 and 0.033, respectively). Short pulse and high energy were significant risk factors for fiber fracture using the 365 µm fibers (p = 0.02), but not for the 272 µm fibers (p = 0.35). Frequency was not a risk factor for fiber rupture. Fiber diameters also seemed to be involved in the failure with a higher number of broken fibers for the 365 µm fibers, but this was not statistically significant when compared with the 272 µm fibers (p > 0.05). CONCLUSION: Small-core fibers are more resistant than large-core fibers as lower bending diameters (<9 mm) are required to break smaller fibers. In acute angles, the use of small-core fibers, at a low energy and long-pulse (dusting) setting, will reduce the risk of fiber rupture.

Laser Fiber and Flexible Ureterorenoscopy: The Safety Distance Concept.

INTRODUCTION: The costs of flexible ureterorenoscopes (fURSs) and their repair oblige the surgeon to know the proper handling of instruments. There is a lack of evidence in the literature about the safety distance that the laser fiber should have once out from the ureterorenoscope to avoid instrumental damages. MATERIALS AND METHODS: We performed an in vitro observational study. Seven fURSs were tested. The distance from the laser fiber tip and the fURS camera was measured at the first appearance on the endoscopic screen and when the fiber was reaching one-fourth of the screen. Second, to evaluate the impact of the holmium laser bubble according to different fiber distances, an assessment of the size and shape of the bubble created at the tip of the fiber with the laser activated was done, recording the images with a high-speed camera. RESULTS: The first appearance on the screen of the laser tip is different in different ureterorenoscopes. In all the ureterorenoscopes, we observed that when the laser fiber was at » of the screen, the bubble was never touching the fURS tip. CONCLUSION: Even if there is a big limitation of this study due to the impossibility to measure and to evaluate the damage of the fURS tip surface, we observed that when the laser fiber tip reaches » of the screen, the bubble generated by laser activation is never rebounding on the camera of the ureterorenoscope, preserving it from laser damages. We can define this position as the safety distance.