Stone Retropulsion with Ho: YAG and Tm: YAG Lasers: A Clinical Practice-Oriented Experimental Study

What to expect from the novel pulsed thulium:YAG laser? A systematic review of endourological applications

INTRODUCTION

Several preclinical studies about a novel pulsed-thulium:yttrium-aluminum-garnet (p-Tm:YAG) device have been published, demonstrating its possible clinical relevance.

METHODS

We systematically reviewed the reality and expectations for this new p-Tm:YAG technology. A PubMed, Scopus and Embase search were performed. All relevant studies and data identified in the bibliographic search were selected, categorized, and summarized.

RESULTS

Tm:YAG is a solid state diode-pumped laser that emits at a wavelength of 2013 nm, in the infrared spectrum. Despite being close to the Ho:YAG emission wavelength (2120 nm), Tm:YAG is much closer to the water absorption peak and has higher absorption coefficient in liquid water. At present, there very few evaluations of the commercially available p-Tm:YAG devices. There is a lack of information on how the technical aspects, functionality and pulse mechanism can be maximized for clinical utility. Available preclinical studies suggest that p-Tm:YAG laser may potentially increase the ablated stone weight as compared to Ho:YAG under specific condition and similar laser parameters, showing lower retropulsion as well. Regarding laser safety, a preclinical study observed similar absolute temperature and cumulative equivalent minutes at 43° C as compared to Ho:YAG. Finally, laser-associated soft-tissue damage was assessed at histological level, showing similar extent of alterations due to coagulation and necrosis when compared with the other clinically relevant lasers.

CONCLUSIONS

The p-Tm:YAG appears to be a potential alternative to the Ho:YAG and TFL according to these preliminary laboratory data. Due to its novelty, further studies are needed to broaden our understanding of its functioning and clinical applicability.

New Lasers for Stone Treatment

Laser technology has been a breakthrough in urology. The new era in endocorporeal laser lithotripsy has recently begun in mid-2020, where promising technologies tested in vitro have reached their approval for clinical use and, in that way, have made it possible to confirm their safety and advantages in the real world, for the patient and for the urologist.

Stone retropulsion caused by the pulse-duration adjustable Holmium laser: analysis of the whole-process dynamics with a modified method

INTRODUCTION

Stone retropulsion was shown to be impacted by pulse duration during Holmium laser lithotripsy, while the whole process of retropulsion was troublesome to study. We developed a modified method to analyze retropulsion using a smartphone and video tracking software.

MATERIALS AND METHODS

A Holmium laser system was incorporated with a short (200 μs) and long pulse duration (800 μs), and a 272 μm core fiber was attached. A cross-sectional V-shaped rail was submerged in a tank, on which artificial stones were displaced linearly after lasering. Different combinations of pulse energy, frequency and pulse duration were tested for at least four seconds. An iPhone 11 capable of high-definition videoing and video tracking software were used to analyze the stone's displacement and velocity.

RESULTS

For most settings, the displacement-time graph resembled logarithmic growth and the velocity peaked within the first second after lasering. Higher energy or frequency translated into greater displacement, accompanied by earlier and faster velocity peaks. When the laser power was constant, the stone displacement at the fourth second after lasering was much larger in 0.5 J × 40 Hz than 1.0 J × 20 Hz under the short pulse duration (SP) (13.17 ± 0.92 mm vs. 6.90 ± 1.98 mm, p < 0.05), but this discrepancy was offset by the long pulse duration (LP). The largest stone displacement and velocity were observed in 0.5 J × 40 Hz SP.

CONCLUSION

The pulse duration plays a dominant role in determining the stone retropulsion and velocity, and a long pulse decreases retropulsion and velocity. Given a constant power, the variable combination of frequency and pulse energy contributes to significantly different retropulsion with a short pulse rather than a long pulse. The modified method offers a feasible solution for the study of stone retropulsion by laser lithotripsy.

"VirtualBasket" ureteroscopic holmium laser lithotripsy: intraoperative and early postoperative outcomes

BACKGROUND

The "VirtualBasket" technology is the result of pulse modulation during holmium laser emission: the laser emits part of the energy to create an initial bubble, and a second pulse is emitted when the vapor bubble is at its maximum expansion, so that it can pass through the previously created vapor channel. The aim of this study is to outline the outcomes of the "VirtualBasket" technology in ureteral and renal stones.

METHODS

160 Patients were randomly assigned to holmium laser lithotripsy with or without the "VirtualBasket" technology in ureteric or renal cases (40 per 4 groups). All procedures were performed by four experienced urologists. The Quanta System Cyber Ho 100W laser generator with 365 μm fibers was used for all of the ureteral cases, whereas, 272 μm fibers were used for all of the cases in the renal pelvis. Demographic data, stone parameters, perioperative complications and success rates were compared. A statistical analysis was carried out to assess patients data and outcomes. All of the reported p-values were obtained with the two-sided exact method at the conventional 5% significance level. The degree of stone retropulsion was graded on a Likert scale from zero (no retropulsion) to 3 (maximum retropulsion).

RESULTS

All groups were comparable in terms of age, and pre-operative stone size (ureter stone size: 1.2 vs. 1.1 cm; renal pelvis stone size: 1.55 vs. 1.62 cm). Compared to the regular mode, the "VirtualBasket" technology was associated with significantly lower fragmentation time (mean time for ureteral stones: 20.4 vs. 16.1 minutes, p<0.05; mean time for renal stones: 28.7 vs. 19.8 minutes, p<0.05) and total procedural time (mean time for ureteral stones 49 vs. 35.7 minutes; mean time for renal stones 67.1 vs. 52.4 minutes). There were no significant differences in terms of energy delivered to the stones, intraoperative complications and success rate at 1 month. The "VirtualBasket" technology was associated with significantly lower retropulsion.

CONCLUSIONS

The "VirtualBasket" technology is associated with significantly lower fragmentation and procedural times. The reduced fragmentation time is a result of the significantly lower retropulsion of the stones during laser lithotripsy, which improves stone fragmentation efficiency.

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.

Dusting, fragmenting, popcorning or dustmenting?

PURPOSE OF REVIEW

The present review identifies the latest scientific investigations within the fields of fragmenting and dusting to discuss optimizing treatment. In addition, new settings such as 'popcorning' are scrutinized carefully.

RECENT FINDINGS

During the past years, endoscopic techniques have continuously developed and changed the management of the treatment of kidney stones using ureteroscopy (URS). The most currently used energy source for stone disintegration is holmium laser lithotripsy. This technique offers different options for the surgeons to treat their patients suffering from kidney stones.

SUMMARY

URS with the holmium laser allows surgeons to use a variety of different strategies for treating urinary stones. There are two techniques which are most frequently used within this field: firstly fragmenting, using low frequencies and high pulse energy to break stones into small fragments before removal. On the other hand, dusting has been popularized in the field of endourology in recent years. This uses high frequencies and low pulse energy to form fine dust particles which then pass spontaneously down the ureter.

Assessing Cost-Effectiveness of New Technologies in Stone Management

Diagnosis, treatment, and follow-up are all influential in determining the overall cost to the health care system for kidney stones. New innovations in the field of nephrolithiasis have been abundant, including disposable ureteroscopes, ultrasound-guided approaches to percutaneous nephrolithotomy, and advanced laser lithotripters. Identifying cost-effective treatment strategies encourages practitioners to be thoughtful about providing value-based high-quality care and remains on important principle in the treatment of urinary stone disease.

Recent advances in infrared laser lithotripsy [Invited]

The flashlamp-pumped, solid-state, pulsed, mid-infrared, holmium:YAG laser (λ = 2120 nm) has been the clinical gold standard laser for lithotripsy for over the past two decades. However, while the holmium laser is the dominant laser technology in ureteroscopy because it efficiently ablates all urinary stone types, this mature laser technology has several fundamental limitations. Alternative, mid-IR laser technologies, including a thulium fiber laser (λ = 1908 and 1940 nm), a thulium:YAG laser (λ = 2010 nm), and an erbium:YAG laser (λ = 2940 nm) have also been explored for lithotripsy. The capabilities and limitations of these mid-IR lasers are reviewed in the context of the quest for an ideal laser lithotripsy system capable of providing both rapid and safe ablation of urinary stones.

Advances in Lasers for the Treatment of Stones-a Systematic Review

PURPOSE OF REVIEW

Laser lithotripsy is increasingly used worldwide and is a continuously evolving field with new and extensive research being published every year.

RECENT FINDINGS

Variable pulse length Ho:YAG lithotripters allow new lithotripsy parameters to be manipulated, and there is an effort to integrate new technologies into lithotripters. Pulsed thulium lasers seem to be a viable alternative to holmium lasers. The performance of similar laser fibers varies from manufacturer to manufacturer. Special laser fibers and "cleaving only" fiber tip preparation can be beneficial for the lithotripsy procedure. Different laser settings and the surgical technique employed can have significant impact on the success of laser lithotripsy. When safely done, complications of laser lithotripsy are rare and concern the endoscopic nature of procedure, not the technology itself, making laser lithotripsy one of the safest tools in urology. Laser lithotripsy has had several new developments and more insight has been gained in recent years with many more advances expected in the future.

In vitro investigations of propulsion during laser lithotripsy using video tracking

OBJECTIVES

Ureteroscopic laser lithotripsy is an important and widely used method for destroying ureter stones. It represents an alternative to ultrasonic and pneumatic lithotripsy techniques. Although these techniques have been thoroughly investigated, the influence of some physical parameters that may be relevant to further improve the treatment results is not fully understood. One crucial topic is the propulsive stone movement induced by the applied laser pulses. To simplify and speed up the optimization of laser parameters in this regard, a video tracking method was developed in connection with a vertical column setup that allows recording and subsequently analyzing the propulsive stone movement in dependence of different laser parameters in a particularly convenient and fast manner.

MATERIALS AND METHODS

Pulsed laser light was applied from below to a cubic BegoStone phantom loosely guided within a vertical column setup. The video tracking method uses an algorithm to determine the vertical stone position in each frame of the recorded scene. The time-dependence of the vertical stone position is characterized by an irregular series of peaks. By analyzing the slopes of the peaks in this signal it was possible to determine the mean upward stone velocity for a whole pulse train and to compare it for different laser settings. For a proof of principle of the video tracking method, a specific pulse energy setting (1 J/pulse) was used in combination with three different pulse durations: short pulse (0.3 ms), medium pulse (0.6 ms), and long pulse (1.0 ms). The three pulse durations were compared in terms of their influence on the propulsive stone movement in terms of upward velocity. Furthermore, the propulsions induced by two different pulse energy settings (0.8 J/pulse and 1.2 J/pulse) for a fixed pulse duration (0.3 ms) were compared. A pulse repetition rate of 10 Hz was chosen for all experiments, and for each laser setting, the experiment was repeated on 15 different freshly prepared stones. The latter set of experiments was compared with the results of previous propulsion measurements performed with a pendulum setup.

RESULTS

For a fixed pulse energy (1 J/pulse), the mean upward propulsion velocity increased (from 120.0 to 154.9 mm · s^-1 ) with decreasing pulse duration. For fixed pulse duration (0.3 ms), the mean upward propulsion velocity increased (from 91.9 to 123.3 mm · s^-1 ) with increasing pulse energy (0.8 J/pulse and 1.2 J/pulse). The latter result corresponds roughly to the one obtained with the pendulum setup (increase from 61 to 105 mm · s^-1 ). While the mean propulsion velocities for the two different pulse energies were found to differ significantly (P < 0.001) for the two experimental and analysis methods, the standard deviations of the measured mean propulsion velocities were considerably smaller in case of the vertical column method with video tracking (12% and 15% for n = 15 freshly prepared stones) than in case of the pendulum method (26% and 41% for n = 50 freshly prepared stones), in spite of the considerably smaller number of experiment repetitions ("sample size") in the first case.

CONCLUSION

The proposed vertical column method with video tracking appears advantageous compared to the pendulum method in terms of the statistical significance of the obtained results. This may partly be understood by the fact that the entire motion of the stones contributes to the data analysis, rather than just their maximum distance from the initial position. The key difference is, however, that the pendulum method involves only one single laser pulse in each experiment run, which renders this method rather tedious to perform. Furthermore, the video tracking method appears much better suited to model a clinical lithotripsy intervention that utilizes longer series of laser pulses at higher repetition rates. The proposed video tracking method can conveniently and quickly deliver results for a large number of laser pulses that can easily be averaged. An optimization of laser settings to achieve minimal propulsive stone movement should thus be more easily feasible with the video tracking method in connection with the vertical column setup. Lasers Surg. Med. 50:333-339, 2018. © 2017 Wiley Periodicals, Inc.

Intracorporeal lithotripsy

Since the introduction of ESWL, PNL and URS during the early 1980s the application rate of ESWL has declined while those of PNL and URS have increased. This is mainly due to the facts that instruments and techniques for Intracorporeal Lithotripsy (IL) have made a continuous progress. This review shows that today an array of options for IL within the entire urinary tract is available to treat stones in a perfect minimal invasive way. At the same time further improvements of IL are already visible.

Holmium Laser Lithotripsy in the New Stone Age: Dust or Bust?

Modern day holmium laser systems for ureteroscopy (URS) provide users with a range of settings, namely pulse energy (PE), pulse frequency (Fr), and pulse width (PW). These variables allow the surgeon to choose different combinations that have specific effects on stone fragmentation during URS lithotripsy. Contact laser lithotripsy can be performed using fragmentation or dusting settings. Fragmentation employs settings of low Fr and high PE to break stones that are then extracted with retrieval devices. Dusting is the utilization of high Fr and low PE settings to break stones into submillimeter fragments for spontaneous passage without the need for basket retrieval. Use of the long PW mode during lithotripsy can reduce stone retropulsion and is increasingly available in new generation lasers. During non-contact laser lithotripsy, stone fragments are rapidly pulverized in a calyx in laser bursts that result in stones breaking into fine fragments. In this review, we discuss the effect of different holmium laser settings on stone fragmentation, and the clinical implications in a very much evolving field.

Fiber optic muzzle brake tip for reducing fiber burnback and stone retropulsion during thulium fiber laser lithotripsy

The experimental thulium fiber laser (TFL) is being explored as an alternative to the current clinical gold standard Holmium:YAG laser for lithotripsy. The near single-mode TFL beam allows coupling of higher power into smaller optical fibers than the multimode Holmium laser beam profile, without proximal fiber tip degradation. A smaller fiber is desirable because it provides more space in the ureteroscope working channel for increased saline irrigation rates and allows maximum ureteroscope deflection. However, distal fiber tip burnback increases as fiber diameter decreases. Previous studies utilizing hollow steel sheaths around recessed distal fiber tips reduced fiber burnback but increased stone retropulsion. A “fiber muzzle brake” was tested for reducing both fiber burnback and stone retropulsion by manipulating vapor bubble expansion. TFL lithotripsy studies were performed at 1908 nm, 35 mJ, 500 ?? ? s , and 300 Hz using a 100 - ? m -core fiber. The optimal stainless steel muzzle brake tip tested consisted of a 1-cm-long, 560 - ? m -outer-diameter, 360 - ? m -inner-diameter tube with a 275 - ? m -diameter through hole located 250 ?? ? m from the distal end. The fiber tip was recessed a distance of 500 ?? ? m . Stone phantom retropulsion, fiber tip burnback, and calcium oxalate stone ablation studies were performed ex vivo. Small stones with a mass of 40 ± 4 ?? mg and 4-mm-diameter were ablated over a 1.5-mm sieve in 25 ± 4 ?? s