Holmium:yttrium-aluminum-garnet laser induced lithotripsy: in-vitro investigations on fragmentation, dusting, propulsion and fluorescence

The assistive role of an internal fluid circulatory device in ureteroscopic lithotripsy: a randomized, controlled and prospective study

PURPOSE

To evaluate and compare the efficacy of a newly designed in-house assistive internal fluid circulatory device in ureteroscopic lithotripsy for ureteral stones.

METHODS

In this study, 97 patients were assigned to the trial group and underwent ureteroscopic lithotripsy with an in-house newly designed assistive internal fluid circulatory device; 96 patients were assigned to the control group and underwent traditional ureteroscopic lithotripsy without the assistive device. The primary outcome was the final stone-free rate (SFR) at 1-month post-surgery. Secondary observations included the quality of the surgical field, difficulty experienced during insertion of the ureteroscope, stone migration rate, operative time, change in serum creatinine, changes in the urinary leukocyte count, and perioperative complications.

RESULTS

No significant differences were detected between the two groups in terms of gender, age, body mass index, location, or stone burden (P > 0.05). At the 1-month follow-up, the SFR was significantly higher in the trial group than the control group (P < 0.05). Furthermore, the operative time was significantly shorter in the trial group (P < 0.05) with easier ureteroscope insertion relative to the control group (P < 0.05). The incidence of stone migration in the trial group was significantly lower than that in the control group (P < 0.05) and the quality of the surgical field was significantly improved (P < 0.001). No significant differences were detected in terms of serum creatinine levels, urinary leukocyte counts, or perioperative complications (P > 0.05).

CONCLUSIONS

The application of an assistive internal fluid circulatory device represents an effective and safe method for ureteroscopic lithotripsy.

Stone dust in endourology: a systematic review of its definition, management, and clinical impact

OBJECTIVE

To evaluate and synthesise the existing literature on stone dust (DUST) in endourology, focusing on its definition, creation methods, and removal techniques.

METHODS

A comprehensive electronic literature search was conducted using the PubMed/Medline, Web Of Science, and Embase databases to identify reports published until October 2024. The Preferred Reporting Items for Systematic Reviews and Meta-analyses guidelines were followed to identify eligible studies. The outcomes assessed included the definition of DUST, the method by which DUST was created, and how it was removed, evaluating both in vitro and in vivo studies. The review also assessed the efficacy of different laser technologies, including holmium-yttrium-aluminium-garnet (Ho:YAG) laser, thulium fibre laser (TFL), and pulsed thulium-YAG laser (p-Tm:YAG) laser, in generating DUST and their clinical relevance in stone management.

RESULTS

The systematic review identified 43 eligible studies, revealing significant variability in the definition and evaluation of DUST. Criteria for DUST ranged from sub-millimetre particle sizes to functional properties like floatability and aspiration capability. While Ho:YAG lasers remain widely used for stone dusting, emerging technologies such as TFL and p-Tm:YAG lasers have shown superior efficiency in producing finer particles and reducing retropulsion. No consensus emerged regarding the settings used by surgeons and the pre-settings provided by laser manufacturers.

CONCLUSIONS

Despite the widespread use of dusting techniques in endourology, a standardised definition of DUST remains lacking, with significant variability in laser settings, particle sizes, and evacuation methods. It must be clarified whether DUST should be defined as a noun-representing a distinct entity with a precise definition-or as the result of the dusting process, in which case clear criteria are needed to characterise it accurately. Establishing standardised definitions and protocols through international consensus is crucial to optimising clinical outcomes and ensuring consistency in future research.

Intracorporeal lithotripsy of salivary stones: in vitro comparison of different methods

PURPOSE

Intracorporeal lithotripsy is a gland-preserving treatment option for sialolithiasis. Laser lithotripsy (LL) and pneumatic lithotripsy (PL) are the only two methods currently approved, the latter being no longer available. Electrokinetic lithotripsy (EKL) is a promising alternative used for the treatment of ureteral stones. The aim of this study is to compare efficacy and therapeutical safety of EKL with LL and PL.

METHODS

StoneBreaker® (PL), Lithotron EL 27 Compact (EKL) and Ho:YAG laser Auriga (LL) were assessed using in vitro setups with human salivary stones, casted and tumbled stones. Efficacy was measured by the number of impulses and time taken until fragmentation. Parameters for therapeutical safety were number of impulses until perforation, propulsion, duct widening, number of tears and tear length.

RESULTS

Efficacy of EKL was higher than LL but lower than PL. The fragmentation of casted stones took 01:50 ± 00:28 min with PL, 02:49 ± 00:37 min with EKL and 05:12 ± 00:58 min with LL (Mann-Whitney-U test p < 0.01). LL caused the lowest propulsion (0.0 ± 0 cm, n = 20); the highest propulsion was observed for PL (3.5 ± 0.7 cm, n = 20). In the gelatin setup, LL induced the most extensive damage (damage index: 5.9 ± 2.9, n = 15). LL was the fastest to cause perforation in the parotid duct (1 ± 0 impulses until perforation, n = 10).

CONCLUSION

Efficacy and safety of EKL are between those of LL and PL. Therefore, clinical testing of EKL seems to be justified.

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

Introduction

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.

Materials and Methods

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).

Results

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.

Conclusion

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.

Theoretical and experimental evaluation of the distance dependence of fiber-based fluorescence and reflection measurements for laser lithotripsy

OBJECTIVES

In laser lithotripsy, a green aiming beam overlying the infrared (IR) treatment radiation gives rise to reflection and fluorescence signals that can be measured via the treatment fiber. While stone autofluorescence is used for target detection, the condition of the fiber can be assessed based on its Fresnel reflection. For good applicability, fluorescence detection of stones should work even when the stone and fiber are not in direct contact. Fiber breakage detection, on the other hand, can be falsified if surfaces located in front of the fiber reflect light from the aiming laser back into it. For both applications, therefore, a fundamental investigation of the dependence of the signal amplitude on the distance between fiber and surface is important.

METHODS

Calculations of the signal drop of fluorescence or diffuse and specular reflection with increasing fiber distance were performed using ray tracing based on a simple geometric model for different fiber core diameters. Reflection signals from a mirror, diffuse reflector, human calculi, and porcine renal tissue placed in water were measured at varying distances (0 - 5 mm). For human calculi, fluorescence signals were recorded simultaneously.

RESULTS

The calculations showed a linear signal decrease down to ~60% of the maximum signal (fiber in contact). The distance z at which the signal drops to for example 50% depends linearly on the diameter of the fiber core. For fibers used in lithotripsy and positioned in water,z_50%ranges from 0.55 mm (200 µm core diameter) to 2.73 mm (1 mm core diameter). The calculations were in good agreement with the experimental results.

CONCLUSIONS

The autofluorescence signals of stones can be measured in non-contact mode. Evaluating the Fresnel signal of the end face of the fiber to detect breakage is possible unless the fiber is situated less than some millimeters to reflecting surfaces.

Efficiency and Clinical Outcomes of Moses Technology with Flexible Ureteroscopic Laser Lithotripsy for Treatment of Renal Calculus

OBJECTIVE

The aim of the study was to compare the efficiency and clinical outcomes of Moses contact mode (MCM) and regular dusting mode (RDM) during flexible ureteroscopic lithotripsy (FURL) for treatment of renal calculus.

METHODS

This retrospective analysis examined 216 patients with renal calculus who underwent FURL with MCM or RDM between March 2015 and January 2020. Stone characteristics, including size, volume, and density, were collected. Laser parameters, including laser type, laser working time, laser pause time, and foot-pedal use, were automatically recorded by the lithotripter work panel. The percentages of laser working time and laser pause time, stone fragmentation efficiency (SFE; volume/laser working time), postoperative complications, including fever and acute renal failure (ARF), stone-free rate (SFR), and the need for auxiliary procedures were determined.

RESULTS

There were no significant differences in preoperative demographic and stone characteristics between the MCM group and the RDM group. The MCM group had a shorter laser working time (4.99 ± 1.06 vs. 5.94 ± 0.96 min, p < 0.001) and a greater SFE (137.86 [163.78-114.38] versus 114.94 [132.06-101.34] mm3/min, p < 0.001), which shortened the overall operative time (18.39 ± 5.13 vs. 21.17 ± 6.78 min, p = 0.001). There were no differences in postoperative complications, including fever and ARF, SFR (86.8 vs. 85.3%, p = 0.743), and auxiliary procedures between the 2 groups.

CONCLUSIONS

Using Moses laser technology with FURL significantly reduced laser working time and increased SFE, which shortened overall operative time. Urologists should consider this new instrument for the clinical management of renal calculus.

Retropulsion force in laser lithotripsy-an in vitro study comparing a Holmium device to a novel pulsed solid-state Thulium laser

PURPOSE

To investigate retropulsion forces generated by two laser lithotripsy devices, a standard Ho:YAG and a new pulsed solid-state Thulium laser device.

MATERIALS AND METHODS

Two different Dornier laser devices were assessed: a Medilas H Solvo 35 and a pulsed solid-state Thulium laser evaluation model (Dornier MedTech Laser GmbH, Wessling, Germany). We used a 37 °C water bath; temperature was monitored with a thermocouple/data-logger. Representative sets of settings were examined for both devices, including short and long pulse lengths where applicable. For each setting, ten force values were recorded by a low-force precision piezo sensor whereby the laser fibre was either brought into contact with the sensor or placed at a 3 mm distance.

RESULTS

The mean retropulsion forces resulting from the new Tm:YAG device were significantly lower than those of the Ho:YAG device under all pulse energy and frequency settings, ranging between 0.92 and 19.60 N for Thulium and 8.09-39.67 N for Holmium. The contact setups yielded lower forces than the distance setups. The forces increased with increasing pulse energy settings while shorter pulse lengths led to 12-44% higher retropulsive force in the 2.0 J/5 Hz comparisons.

CONCLUSION

The Tm:YAG device not only significantly generated lower retropulsion forces in all comparisons to Holmium at corresponding settings but also offers adjustment options to achieve lower energy pulses and longer pulse durations to produce even lower retropulsion. These advantages are a promising add-on to laser lithotripsy procedures and may be highly relevant for improving laser lithotripsy performance.

Homogeneously Emitting, Mechanically Stable, and Efficient fs-Laser-Machined Fiber Diffusers for Medical Applications

BACKGROUND AND OBJECTIVES

Light delivery is an essential part of therapy forms like photodynamic therapy (PDT), laser-induced thermotherapy, and endovenous laser therapy. While there are approaches to the light application for all three therapies, there is no diffuser that can be used for all three approaches. This diffuser must meet the following criteria: Homogeneous radiation profile over a length of 40 mm, efficient light extraction in the diffuser area, mechanical breakage resistance as well as thermal stability when applying high power.

STUDY DESIGN/MATERIALS AND METHODS

An ultrashort pulse laser was used to inscribe inhomogeneities into the core of a fused-silica fiber core while scanning the laser focus within a linear arrangement of cuboids centered around the fiber axis. The manufactured diffuser was optically and mechanically characterized and examined to determine the maximum power that can be applied in a tissue environment.

RESULTS

Based on the analysis of all examined diffusers, the manufactured diffuser exhibits an emission efficiency ε = (81.5 ± 5.9)%, an intensity variability of (19 ± 5)% between distal and proximal diffuser end, and a minimum bending radius R_b = (15.4 ± 1.5) mm. It was taken advantage of the fact that the outer areas of the fiber core do not undergo any structural changes due to the machining and therefore do not suffer a major loss of stability. Tissue experiments revealed that a maximal power of 15 W was deliverable from the diffuser without harming the diffuser itself.

CONCLUSIONS

It could be shown that a diffuser manufactured by ultrafast-laser processing can be used for low power applications as well as for high power applications. Further tests have to show whether the mechanical stability is still maintained after the application of high power in a tissue environment. Lasers Surg. Med. © 2020 Wiley Periodicals LLC.

Surface modifications of optical fiber ferrule for diffusive optical-thermal transport

The current study aimed to develop surface modifications of a capillary ferrule to avoid misalignment-related thermal damage in the fiber connector and the eventual fiber failure during high-power laser lithotripsy. Numerical analysis showed that the modified surface diffused leaking rays (high-order modes) from the misalignment. The light diffusion subsequently confined absorption-induced heat accumulation to the stainless steel connector tip (used as heat sink). Light-offset experiments validated minimal transient and steady-state heating of the modified connector surface with no thermal damage in the connector due to diffusive optical-thermal transport. The ferrule surface modifications may prevent fiber failure during the lithotripsy.

Exploiting the aiming beam to increase the safety of laser lithotripsy: Experimental evaluation of light reflection and fluorescence

BACKGROUND AND OBJECTIVES

In Holmium laser lithotripsy, usually, the surgeon is guided by a visible beam superimposing the infrared (IR) treatment radiation. It has been shown that a green aiming beam excites stone autofluorescence. This fluorescence signal can be used for calculi detection to check the correct fiber position before triggering the IR laser, thus preventing damage to soft tissue and application devices. However, also the directly reflected green light from the fiber tip gives valuable information on fiber position and its surface condition.

MATERIALS AND METHODS

An external fiber-fiber-coupling-box (fiber core diameter 365 µm) for pulsed holmium laser radiation (2.1 µm) was set up containing a green diode laser module (520 nm, average power on the sample <0.5 mW) and optics and detectors for measuring the reflected light of this aiming beam as well as the fluorescence excited with it. Measurements were done via a lock-in technique with more than 20 human calculi samples and porcine calix in vitro. After the implementation of automatic data storage signals during ongoing in vitro lithotripsy procedures were recorded with the fiber positioned on tissue, stone, or in/on medical equipment (working channel of an endoscope, stone retrieval basket).

RESULTS

Stone fluorescence signals measured were a factor of 7 to >100 higher than those of tissue. Stone fluorescence was detectable in "non-contact mode" with a linear signal decrease over a distance up to ~1 mm in front of the fiber tip (core diameter 365 µm) and with severely damaged fibers (max. decrease: 75% with pinched off fiber). Reflection signals of the fiber tip surface in air and water surrounding decreased significantly when the fiber was damaged; measured ratios of intact to damaged fiber found in the air were (5-17):1 and in water (1.6-3.7):1. Surfaces in front of the fiber aggravated the evaluation of fiber condition due to reflections but enabled to detect, for example, the working channel of a flexible endoscope in combination with the (missing) fluorescence signal.

CONCLUSIONS

Autofluorescence induced by a green aiming beam can be exploited for stone detection in laser lithotripsy. A reflection measurement can give further information on fiber condition and position. Implementing this kind of safety features for an automatic block of IR laser emission in case of weak or missing fluorescence and un-normal reflections can assist the surgeon by avoiding tissue perforation, and damage to medical devices such as endoscopes. Lasers Surg. Med. © 2019 Wiley Periodicals, Inc.

High power holmium:YAG versus thulium fiber laser treatment of kidney stones in dusting mode: ablation rate and fragment size studies

OBJECTIVES

The experimental Thulium fiber laser (TFL) is currently being studied as a potential alternative to the gold standard Holmium:YAG laser for lithotripsy. Recent advances in both Holmium and TFL technology allow operation at similar laser parameters for direct comparison. The use of a "dusting" mode with low pulse energy (0.2-0.4 J) and high pulse rate (50-80 Hz) settings, is gaining popularity in lithotripsy due to the desire to produce smaller residual stone fragments during ablation, capable of being spontaneously passed through the urinary tract.

METHODS

In this study, Holmium and TFL were directly compared for 'dusting' using three laser groups, G1: 0.2 J/50 Hz/10 W; G2: 0.2 J/80 Hz/16 W; and G3: 0.4 J/80 Hz/32 W. Holmium laser pulse durations ranged from 200 to 350 μs, while TFL pulse durations ranged from 500 to 1,000 μs, due to technical limitations for both laser systems. An experimental setup consisting of 1 × 1 cm cuvette with 1 mm sieve was used with continuous laser operation time limited to ≤5 minutes. Calcium oxalate monohydrate stone samples with a sample size of n = 5 were used for each group, with average initial stone mass ranging from 216 to 297 mg among groups.

RESULTS

Holmium laser ablation rates were lower than for TFL at all three settings (G1: 0.3 ± 0.2 vs. 0.8 ± 0.2; G2: 0.6 ± 0.1 vs. 1.0 ± 0.4; G3: 0.7 ± 0.2 vs. 1.3 ± 0.9 mg/s). The TFL also produced a greater percentage by mass of stone dust (fragments <0.5 mm) than Holmium laser. For all three settings combined, one out of 15 (7%) stones treated with Holmium laser were completely fragmented in ≤5 minutes compared to nine out of 15 (60%) stones treated with TFL.

CONCLUSIONS

These preliminary studies demonstrate that the TFL is a promising alternative laser for lithotripsy when operated in dusting mode, producing higher stone ablation rates and smaller stone fragments than the Holmium laser. Clinical studies are warranted. Lasers Surg. Med. 51:522-530, 2019. © 2019 Wiley Periodicals, Inc.