Comparison of Different Pulse Modulation Modes for Holmium:Yttrium-Aluminum-Garnet Laser Lithotripsy Ablation in a Benchtop Model

Effect of Pulse Modulation on Diode-Pumped Laser Lithotripsy

Introduction: This study addresses pulse modulation for kidney stone lithotripsy using diode-pumped thulium yttrium aluminum garnet (Tm:YAG, λ = 2.02 µm) and thulium fiber lasers (TFLs, λ = 1.94 µm). Three research questions were investigated: (1) What are the effects of varying pulse duration and energy of the first pulse and varying the interpulse delay in a pulse modulation sequence to increase energy transfer across saline to a stone? (2) Does an optimal pulse modulation profile exist in a single-pulse sequence to provide highest percent radiant energy transfer? (3) Does a higher effective energy transfer to the stone using pulse modulation produce greater stone volumetric removal? Materials and Methods: We measured radiant energy transmission efficiency (RETE) and ablation volumes in phantom and human stones. RETE was utilized to compare the pulse energy transmission through air and saline media. We recorded fast camera traces and vapor bubble collapse pressures. Craters were created at fiber standoff distances (SDs) of 0.0 mm, 0.5 mm, and 1.0 mm, and volumes were measured using optical coherence tomography. Results: For Tm:YAG laser irradiation, dual-pulse mode significantly increased RETE by as much as 75% at 1 mm SD compared with single-pulse mode. With the Tm:YAG laser, an optimal "dual-pulse" modulation resulted in greater volumetric removal compared with a "single-pulse" across all stone cohorts (p < 0.05) except for calcium oxalate monohydrate stones (p = 0.38) at a 1 mm SD. TFL yielded similar results, but showed heterogeneity across stone compositions. Conclusions: Pulse-modulated diode-pumped Tm:YAG and TFL can deliver higher photon count through a saline layer if the first pulse is optimized. An optimal pulse modulation profile where the second pulse is synchronized with the vapor bubble dynamics of the first pulse results in the highest percent RETE and increased stone volumetric removal.

Optimal stone density for ablation lithotripsy with vapor tunnel Ho:YAG pulse modality

INTRODUCTION

Vapor-Tunnel™ (VT) consists of a very long pulse that uses the minimum peak power, causing the energy to pass through a previously created vapor channel or tunnel. There are studies that have shown acceptable ablation lithotripsy efficiency. Nevertheless, there are no in-vivo studies that have compared the VT performance according to the stone density.

METHODS

A retrospective study of 152 patients who underwent RIRS using VT Ho:YAG laser was performed. We divided the patients according to the stone density (Group 1: < 1000UH vs. Group 2: > 1000UH). We assessed the lithotripsy efficiency (mm3/JJ) and the laser-energy consumption (JJ/mm3). The stone-free rate (SFR) was defined as the absence of stone fragments in a non-contrast abdominal computed tomography 4 weeks after the procedure.

RESULTS

Ninety three patients were included in Group 1 and 59 in Group 2. Body mass index was higher in Group 1 and the median stone volume was higher in Group 2 (846 vs. 672 mm3, p = 0.03). Total energy used (11.9 vs. 24 kj, p < 0.001), the laser emission time (19 vs. 30 min, p < 0.001), and the total operative time (60 vs. 85 min, p < 0.001) were lower in the Group 1. SFR was higher in Group 1 (96.7% vs. 57.6%, p < 0.001) with a global SFR of 81.6%. The ablation lithotripsy efficiency was higher in Group 1 (0.053 mm3/JJ vs. 0.035 mm3/JJ, p < 0.001).

CONCLUSIONS

VT Ho:YAG was associated with decreased laser time, operative time and laser-energy consumption in Group 1 than Group 2. Similarly, VT Ho:YAG increased lithotripsy efficiency and the SFR compared to hard stones with the same laser settings and pulse modality.

Characterizing stone ablation with the thulium fiber laser: a single-pulse comparison of different pulse durations

Stone ablation using the thulium fiber laser (TFL) at different pulse duration/peak power or laser fiber-to-stone distances requires further research to understand effective and safe settings. In this study we characterized the vapor bubble anatomy and stone crater morphology at various settings and standoff distances. Optical profiles of 1 J short pulse (SP), 1 J long pulse (LP), 3 J SP, and 2.4 J LP of a TFL system (Fiberdust, Quanta) were assessed. We used high-speed imaging and segmentation to quantify the vapor bubble. Using Begostones, stone craters from a single pulse at each setting were compared at 0, 0.5, 1, 2 and 3 mm standoff distances. The temporal optical profile of TFL is rectangular in shape with a peak power of ~ 180W (LP) and ~ 470W (SP). Increasing the pulse energy did not increase the peak power. LP generated a channel-like bubble while SP formed multiple generations of a spherical bubble. Ablation volume with SP was greater than LP for all distances (p < 0.001) with up to 350% increased crater volume at contact. Ablation reduced as distance increased with both modes. There was no ablation at > 1 mm distance with LP. For SP, increasing the pulse energy had minimal impact on crater depth. The SP creates a bubble geometry that tends to collapse more quickly in comparison to LP. Peak power of TFL is a function of pulse duration, not pulse energy. LP results in weak ablation. When using SP, increasing the pulse energy increased ablation volume by increasing crater area rather than depth.

Is Pulse Modulation the Future of Laser Technology in Endourology: Evidence from a Literature Review - Section of EAU Endourology

BACKGROUND AND OBJECTIVE

The aim of our review was to comprehensively evaluate the impact of pulse modulation technology in the field of endourology, with a focus on laser lithotripsy and prostate enucleation.

METHODS

A systematic search was conducted in the PubMed, MEDLINE, and Scopus databases for articles published during the past 20 yr (January 2004-July 2024). Article selection adhered to the Population, Intervention, Comparator, Outcome (PICO) framework and the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. In vivo, ex vivo, in vitro, and clinical studies that reported on the impact of pulse modulation technologies in laser lithotripsy or prostate enucleation in comparison to a standard references or as a standalone report, with a focus on stone ablation efficiency, safety, tissue ablation, and hemostasis, were eligible. A total of 29 articles were included.

KEY FINDINGS

Pulse modulation is a feature mostly implemented for Ho:YAG laser generators. Preclinical studies on pulse modulation have demonstrated promising results for both stone fragmentation and laser-tissue interaction. Clinical studies that investigated technologies such as the Vapor Tunnel, Virtual Basket, and Moses have revealed better efficiency in comparison to the short-pulse modality. While there have been modest improvements in hemostasis and operating time, there has been no obvious improvement in outcomes after prostate surgery.

CONCLUSIONS AND CLINICAL IMPLICATIONS

While in vitro studies have shown that pulse modulation improves stone fragmentation, reduces retropulsion, and maintains thermal safety, clinical outcomes are more variable. For prostate enucleation, the benefits are less consistent. Pulse modulation may improve efficiency, primarily by reducing operating times, but key outcomes such as stone-free and complication rates remain comparable to those with standard modalities.

PATIENT SUMMARY

Our review shows that pulse modulation technology improves the effectiveness and safety of laser treatments for kidney stones. However, the benefits of this technology for prostate surgery are still uncertain, highlighting the need for more research.

A comparison between vapor tunnel and virtual basket for the treatment of proximal ureteral stones using holmium:YAG laser (Cyber Ho): which is the best tool to reduce retropulsion?

PURPOSE

To compare vapor tunnel (VT) and virtual basket (VB) tools to reduce retropulsion in the treatment of proximal ureteral stones.

METHODS

Patients with a single proximal ureteral stone were randomly assigned to holmium laser lithotripsy with the use of VT (Group A) or VB (Group B) tool. The 150W holmium:YAG cyber Ho generator was used. We compared operative time, dusting time, need for flexible ureteroscopy due to stone push-up and occurrence of ureteral lesions. The stone-free rate (SFR) and the occurrence of postoperative ureteral strictures were assessed.

RESULTS

186 patients were treated, of which 92 with the VT (49.5%, Group A) and 94 with the VB (50.5%, Group B). Mean stone size was 0.92 vs. 0.91 cm in Groups A vs. B (p = 0.32). Mean total operative time and dusting time were comparable between groups. 7 (7.6%) vs. 6 (6.4%) patients in Groups A vs. B required a flexible ureteroscope because of stone push-up (p = 0.12). Ureteral mucosa lesions were observed in 15 (16.3%) vs. 18 (19.1%) cases in the VT vs. VB group (p = 0.09). 1-Month SFR was comparable (97.8% vs. 95.7%, p = 0.41). We observed one case (1.1%) of postoperative ureteral stricture in the VT group vs. two cases (2.1%) in the VB group (p = 0.19).

CONCLUSIONS

VT and VB are equally safe and effective tools in reducing retropulsion of ureteral stones. Operative time, dusting time and SFR were comparable. They also equally avoided stone push-up and prevented ureteral lesions, which may later occur in ureteral strictures.

Advances in lasers for the minimally invasive treatment of upper and lower urinary tract conditions: a systematic review

PURPOSE

Technological advancements in laser lithotripsy are expanding into numerous fields of urology, like ureteroscopy (URS), percutaneous nephrolithotomy (PCNL), and benign and malignant soft-tissue treatments. Since the amount of research regarding lasers in urology has grown exponentially, we present a systematic review of the most recent and relevant advances encompassing all lasers used in urological endoscopic treatment.

METHODS

We performed a literature search using PubMed (May 2023) to obtain information about lasers for urological purposes. We included only recent data from published articles between 2021 and 2023 or articles ahead of print.

RESULTS

Lasers are widely used in lithotripsy for ureteric, renal, and bladder stones, benign prostate surgery, and bladder and upper tract tumor ablation. While the holmium (Ho:YAG) laser is still predominant, there seems to be more emphasis on pulse modulation and newer lasers such as thulium fiber laser (TFL) and pulsed Tm:YAG laser.

CONCLUSION

The use of lasers and related technological innovations have shown increasing versatility, and over time have proven to be invaluable in the management of stone lithotripsy, treatment of benign and malignant prostate diseases, and urothelial tumors. Laser endoscopic treatment is heavily based on technological nuances, and it is essential to know at least the basics of these technologies. Ultimately the choice of laser used depends on its availability, cost, surgeon experience and expertise.

Dusting efficacy between the regular setting of holmium laser (Ho:YAG) versus Vapor Tunnel pulse modality for non-complex kidney stones

The new pulse modality Vapor-Tunnel™ (VT) consists of a very long pulse that uses the minimum peak power, causing the energy to pass through a previously created vapor channel or tunnel. The first part of the pulse creates a vapor channel, whereas the remaining energy is discharged immediately after, passing straight through the previously created tunnel. The aim of this study is to compare the dusting efficacy between Ho:YAG laser with long pulse and Ho:YAG laser with VT for non-complex kidney stones. A retrospective comparative study of 236 patients who underwent retrograde intrarenal surgery using Ho:YAG laser (long pulse vs. VT) was performed. Stone size, stone density, laser settings, laser emission time, and total operative time were recorded. We also assessed the lithotripsy efficacy (J/mm3). The stone-free rate was defined as the absence of stone fragments in a non-contrast abdominal computed tomography 4 weeks after the procedure. A total of 118 patients were included in each group. There was no significant difference in age, gender, and body mass index. Median stone volume (737 mm3 vs. 636 mm3) and stone density (788 HU vs. 656 HU) were higher in the VT group. Total energy used (14.5 J vs. 18.2 J), the laser emission time (20 min vs. 26 min), and the total operative time (79.5 min vs. 95 min) were significantly lower in the VT group. The stone-free rate was comparable between both groups (74.5% for VT and 66.1% for the long-pulse group, p = 0.15). When we evaluated the efficacy of laser lithotripsy, a significantly lower difference was obtained in the VT group (median 12.5 J/mm3 vs. median 23.1 J/mm3). The VT pulse modality was associated with decreased laser time and operative time. Additionally, it increased lithotripsy efficacy compared to Ho:YAG long pulse laser, but with a comparable free-stone rate.

Lasers for stone lithotripsy: advantages/disadvantages of each laser source

PURPOSE

The purpose of this article was to make a narrative review of the literature in search of all articles regarding thulium:yttrium-aluminium-garnet (YAG), thulium laser fiber (TFL) and holmium:YAG (Ho:YAG) for lithotripsy from 2020 to 2023. A selection of articles of special interest and best evidence was made in order to give a better perspective on their advantages and disadvantages.

RECENT FINDINGS

New Ho:YAG technologies of as high power, high frequency and pulsed modulations have shown promising results for lithotripsy by reducing retropulsion with good ablation efficiency. High peak power makes it particularly good for percutaneous nephrolithotomy. High intrarenal temperatures and correct setting are still concerning points.TFL has arrived to be one of the main players in flexible ureteroscopy. Being highly efficient and quick, and by producing micro-dusting the laser is quickly heading to become a gold standard. The new pulsed Thulium YAG is the newest laser. For now, only in-vitro studies show promising results with efficient lithotripsy. As the peak power lies between Ho:YAG and TFL it may be able to adequately perform when needing and low power lithotripsy.

SUMMARY

Several new technologies have been developed in the last years for stone lithotripsy. All being efficient and safe if well used. Different advantages and disadvantages of each laser must be taken into consideration to give each laser the proper indication.

The Effects of Scanning Speed and Standoff Distance of the Fiber on Dusting Efficiency during Short Pulse Holmium: YAG Laser Lithotripsy

To investigate the effects of fiber lateral scanning speed across the stone surface (v_fiber) and fiber standoff distance (SD) on dusting efficiency during short pulse holmium (Ho): YAG laser lithotripsy (LL), pre-soaked BegoStone samples were treated in water using 0.2 J/20 Hz at SD of 0.10~0.50 mm with v_fiber in the range of 0~10 mm/s. Bubble dynamics, pressure transients, and stone damage were analyzed. To differentiate photothermal ablation vs. cavitation damage, experiments were repeated in air, or in water with the fiber tip at 0.25 mm proximity from the ureteroscope end to mitigate cavitation damage. At SD = 0.10 mm, the maximum dusting efficiency was produced at v_fiber = 3.5 mm/s, resulting in long (17.5 mm), shallow (0.15 mm), and narrow (0.4 mm) troughs. In contrast, at SD = 0.50 mm, the maximum efficiency was produced at v_fiber = 0.5 mm/s, with much shorter (2.5 mm), yet deeper (0.35 mm) and wider (1.4 mm), troughs. With the ureteroscope end near the fiber tip, stone damage was significantly reduced in water compared to those produced without the ureteroscope. Under clinically relevant v_fiber (1~3 mm/s), dusting at SD = 0.5 mm that promotes cavitation damage may leverage the higher frequency of the laser (e.g., 40 to 120 Hz) and, thus, significantly reduces the procedure time, compared to at SD = 0.1 mm that promotes photothermal ablation. Dusting efficiency during short pulse Ho: YAG LL may be substantially improved by utilizing an optimal combination of v_fiber, SD, and frequency.

The future of laser technology in kidney stones

PURPOSE OF REVIEW

The aim of this study was to present the recent and promising innovations of the new laser technologies used for the treatment of renal stones.

RECENT FINDINGS

Taking advantage of pulse modulation, new technologies such as the Moses effect, the Virtual basket and the Vapor tunnel have been introduced. These technologies seem to improve lithotripsy efficacy by reducing retropulsion and increasing the stone ablation rate.High-power laser lithotripsy has arisen in everyday clinical practice in some centres. The combination of equal efficacy and safety levels compared with the low-power laser lithotripsy and significantly reduced operative time could explain this trend.Thulium fibre laser is an innovative type of laser-emitting machine that offers a lot of advantages compared with its predecessors. The different mechanism of creating the laser pulse offers new possibilities in laser lithotripsy and perhaps in the future thulium fibre laser could replace Ho:YAG as the golden standard for laser lithotripsy.

SUMMARY

Laser lithotripsy is heavily based on technological equipment. The continuous improvement of available lasers increases the endoscopic lithotripsy levels of efficacy and safety.

New Generation Pulse Modulation in Holmium:YAG Lasers: A Systematic Review of the Literature and Meta-Analysis

(1) Background: New pulse modulation (PM) technologies in Holmium:YAG lasers are available for urinary stone treatment, but little is known about them. We aim to systematically evaluate the published evidence in terms of their lithotripsy performance. (2) Methods: A systematic electronic search was performed (MEDLINE, Scopus, and Cochrane databases). We included all relevant publications, including randomized controlled trials, non-randomized comparative and non-comparative studies, and in-vitro studies investigating Holmium:YAG lithotripsy performance employing any new PM. (3) Results: Initial search yielded 203 studies; 24 studies were included after selection: 15 in-vitro, 9 in-vivo. 10 In-vitro compared Moses with regular PM, 1 compared Quanta’s, 1 Dornier MedTech’s, 2 Moses with super Thulium Fiber Laser, and 1 compared Moses with Quanta PMs. Six out of seven comparative studies found a statistically significant difference in favor of new-generation PM technologies in terms of operative time and five out of six in fragmentation time; two studies evaluated retropulsion, both in favor of new-generation PM. There were no statistically significant differences regarding stone-free rate, lasing and operative time, and complications between Moses and regular PM when data were meta-analyzed. (4) Conclusions: Moses PM seems to have better lithotripsy performance than regular modes in in-vitro studies, but there are still some doubts about its in-vivo results. Little is known about the other PMs. Although some results favor Quanta PMs, further studies are needed.