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

Plasma formation in holmium:YAG laser lithotripsy

OBJECTIVES

During holmium:yttrium-aluminum-garnet (holmium:YAG) laser lithotripsy to break urinary stones, urologists frequently see flashes of light. As infrared laser pulses are invisible, what is the source of light? Here we studied the origin, characteristics, and some effects of flashes of light in laser lithotripsy.

METHODS

Ultrahigh-speed video-microscopy was used to record single laser pulses at 0.2-1.0 J energy lasered with 242 µm glass-core-diameter fibers in contact with whole surgically retrieved urinary stones and hydroxyapatite (HA)-coated glass slides in air and water. Acoustic transients were measured with a hydrophone. Visible-light and infrared photodetectors resolved temporal profiles of visible-light emission and infrared-laser pulses.

RESULTS

Temporal profiles of laser pulses showed intensity spikes of various duration and amplitude. The pulses were seen to produce dim light and bright sparks with submicrosecond risetime. The spark produced by the intensity spike at the beginning of laser pulse generated a shock wave in the surrounding liquid. The subsequent sparks were in a vapor bubble and generated no shock waves. Sparks enhanced absorption of laser radiation, indicative of plasma formation and optical breakdown. The occurrence and number of sparks varied even with the same urinary stone. Sparks were consistently observed at laser energy >0.5 J with HA-coated glass slides. The slides broke or cracked by cavitation with sparks in 63 ± 15% of pulses (1.0 J, N = 60). No glass-slide breakage occurred without sparks (1.0 J, N = 500).

CONCLUSION

Unappreciated in previous studies, plasma formation with free-running long-pulse holmium:YAG lasers can be an additional physical mechanism of action in laser procedures.

Laser accessories: surgical fibers, strippers, cleavers, and protective glasses

PURPOSE OF REVIEW

This review provides most recent findings and developments relating to surgical laser fibers, strippers, cleavers, and protective glasses.

RECENT FINDINGS

The smallest core diameter that can be used with Holmium:YAG lasers is 200 μm. Smaller core diameter fibers can be used with the Thulium fiber laser and offer better flexibility and lower risk of fracture, at the risk of greater burnback effect. Misleading discrepancies between the true diameter of laser fibers and their packaging labels must be considered. Fiber tip degradation from the burnback occurs within few minutes, thus questioning the need for time-consuming fiber tip reprocessing with fiber strippers and special cleaving tools. This shortcoming also applies to instrument-protecting ball-tip fibers. Cleavage of fiber tips through their protective jackets ('coated tips') is a cheaper alternative for instrument protection, additionally offering better visual control of the fiber tip. Third-generation side-firing greenlight laser fibers are still prone to rapid deterioration. Laser eyewear does not seem necessary for Holmium:YAG applications, whereas laser-specific protective glasses should be worn for greenlight laser applications.

SUMMARY

With better understanding of laser accessories, practicing urologists may tailor their practice to reach optimal efficacy and safety for Holmium:YAG, Thulium fiber laser and Greenlight laser applications.

Superpulse thulium fiber laser lithotripsy: an in vitro comparison of 200 μm and 150 μm laser fibers

PURPOSE

To investigate the thermal effects, stone retropulsion and ablation rate of SuperPulse Thulium-fiber laser (SP TFL) with two different surgical fibers of 200 and 150 μm in diameter.

METHODS

SP TFL (NTO IRE-Polus, Fryazino, Russia) performance with 200 and 150 μm fibers (NTO IRE-Polus, Fryazino, Russia) was evaluated. Before each test, the laser fiber was cleaved, and the power measurement was taken to verify the actual laser output power. To compare the laser fibers in well-controlled environments, a number of setups were used to assess retropulsion, ablation efficacy, fiber burnback, energy transmission, and safety.

RESULTS

Power measurements performed before each test revealed a 4.7% power drop for a 200 μm fiber SP TFL (14.3 ± 0.5 W) and 7.3% power drop for a 150 μm fiber SP TFL (13.9 ± 0.5 W) versus the nominally indicated power (15.0 W). Retropulsion with the TFL was minimal and comparable between fibers. We found no clinically relevant temperature differences between SP TFL with either 200 or 150 μm fibers. The ablation efficacy tended to be comparable under most parameters. Yet, we did observe a decreased diameter of residual fragments after the ablation with a 150 μm fiber.

CONCLUSION

The smaller fiber (150 μm) is not inferior to 200 μm fiber in terms of fiber burnback, retropulsion, safety, and ablation rate. Moreover, it has the potential to decrease the diameter of fragments during lithotripsy, which may facilitate dusting during RIRS.

Thulium fiber laser: The new kid on the block

OBJECTIVE

Laser technology in urology is currently used for both stone lithotripsy and prostate enucleation. Thulium fiber laser (TFL) is a novel laser, with initial studies showing potential benefits over other lasers both in terms of its effectiveness and safety profile.

MATERIAL AND METHODS

In the first part of this review, a descriptive analysis of the theoretical concepts behind TFL was performed. This part focused on the physics and laser parameters as applied to the clinical practice. These were interpreted in the context of other lasers, namely, the Holmium:YAG laser to highlight the theoretical advantages as well as potential pitfalls offered by the TFL. In the second part of the review, a narrative synthesis of in-vitro studies regarding TFL and its modifications is performed assessing stone-related parameters, namely, ablation rate, operative time retropulsion, and safety.

RESULTS

TFL achieved high ablation rates in most studies and performed better than Holmium:YAG laser across a range of different settings and ablation modes when the two lasers were compared. Moreover, its ability to use low pulse energy ensures minimal stone retropulsion with the retropulsion threshold estimated to be 2-4 times higher than that of Holmium:YAG laser. From a safety viewpoint, TFL poses no additional risks than other lasers, although it does potentially lead to slightly higher temperatures in the surrounding tissues during lithotripsy.

CONCLUSION

The unique properties of TFL have made it an attractive alternative to conventional laser techniques currently used in urology. Clinical studies are required before its application can become more widespread.

Thulium fiber laser: the new player for kidney stone treatment? A comparison with Holmium:YAG laser

PURPOSE

To compare the operating modes of the Holmium:YAG laser and Thulium fiber laser. Additionally, currently available literature on Thulium fiber laser lithotripsy is reviewed.

MATERIALS AND METHODS

Medline, Scopus, Embase, and Web of Science databases were searched for articles relating to the operating modes of Holmium:YAG and Thulium fiber lasers, including systematic review of articles on Thulium fiber laser lithotripsy.

RESULTS

The laser beam emerging from the Holmium:YAG laser involves fundamental architectural design constraints compared to the Thulium fiber laser. These differences translate into multiple potential advantages in favor of the Thulium fiber laser: four-fold higher absorption coefficient in water, smaller operating laser fibers (50-150 µm core diameter), lower energy per pulse (as low as 0.025 J), and higher maximal pulse repetition rate (up to 2000 Hz). Multiple comparative in vitro studies suggest a 1.5-4 times faster stone ablation rate in favor of the Thulium fiber laser.

CONCLUSIONS

The Thulium fiber laser overcomes the main limitations reported with the Holmium:YAG laser relating to lithotripsy, based on preliminary in vitro studies. This innovative laser technology seems particularly advantageous for ureteroscopy and may become an important milestone for kidney stone treatment.

Advances in laser technology and fibre-optic delivery systems in lithotripsy

The flashlamp-pumped, solid-state holmium:yttrium-aluminium-garnet (YAG) laser has been the laser of choice for use in ureteroscopic lithotripsy for the past 20 years. However, although the holmium laser works well on all stone compositions and is cost-effective, this technology still has several fundamental limitations. Newer laser technologies, including the frequency-doubled, double-pulse YAG (FREDDY), erbium:YAG, femtosecond, and thulium fibre lasers, have all been explored as potential alternatives to the holmium:YAG laser for lithotripsy. Each of these laser technologies is associated with technical advantages and disadvantages, and the search continues for the next generation of laser lithotripsy systems that can provide rapid, safe, and efficient stone ablation. New fibre-optic approaches for safer and more efficient delivery of the laser energy inside the urinary tract include the use of smaller-core fibres and fibres that are tapered, spherical, detachable or hollow steel, or have muzzle brake distal fibre-optic tips. These specialty fibres might provide advantages, including improved flexibility for maximal ureteroscope deflection, reduced cross section for increased saline irrigation rates through the working channel of the ureteroscope, reduced stone retropulsion for improved stone ablation efficiency, and reduced fibre degradation and burnback for longer fibre life.

The laser of the future: reality and expectations about the new thulium fiber laser-a systematic review

The Holmium:yttrium-aluminum-garnet (Ho:YAG) laser has been the gold-standard for laser lithotripsy over the last 20 years. However, recent reports about a new prototype thulium fiber laser (TFL) lithotripter have revealed impressive levels of performance. We therefore decided to systematically review the reality and expectations for this new TFL technology. This review was registered in the PROSPERO registry (CRD42019128695). A PubMed search was performed for papers including specific terms relevant to this systematic review published between the years 2015 and 2019, including already accepted but not yet published papers. Additionally, the medical sections of ScienceDirect, Wiley, SpringerLink, Mary Ann Liebert publishers, and Google Scholar were also searched for peer-reviewed abstract presentations. All relevant studies and data identified in the bibliographic search were selected, categorized, and summarized. The authors adhered to PRISMA guidelines for this review. The TFL emits laser radiation at a wavelength of 1,940 nm, and has an optical penetration depth in water about four-times shorter than the Ho:YAG laser. This results in four-times lower stone ablation thresholds, as well as lower tissue ablation thresholds. As the TFL uses electronically-modulated laser diodes, it offers the most comprehensive and flexible range of laser parameters among laser lithotripters, with pulse frequencies up to 2,200 Hz, very low to very high pulse energies (0.005-6 J), short to very long-pulse durations (200 µs up to 12 ms), and a total power level up to 55 W. The stone ablation efficiency is up to four-times that of the Ho:YAG laser for similar laser parameters, with associated implications for speed and operating time. When using dusting settings, the TFL outperforms the Ho:YAG laser in dust quantity and quality, producing much finer particles. Retropulsion is also significantly reduced and sometimes even absent with the TFL. The TFL can use small laser fibers (as small as 50 µm core), with resulting advantages in irrigation, scope deflection, retropulsion reduction, and (in)direct effects on accessibility, visibility, efficiency, and surgical time, as well as offering future miniaturization possibilities. Similar to the Ho:YAG laser, the TFL can also be used for soft tissue applications such as prostate enucleation (ThuFLEP). The TFL machine itself is seven times smaller and eight times lighter than a high-power Ho:YAG laser system, and consumes nine times less energy. Maintenance is expected to be very low due to the durability of its components. The safety profile is also better in many aspects, i.e., for patients, instruments, and surgeons. The advantages of the TFL over the Ho:YAG laser are simply too extensive to be ignored. The TFL appears to be a real alternative to the Ho:YAG laser and become a true game-changer in laser lithotripsy. Due to its novelty, further studies are needed to broaden our understanding of the TFL, and comprehend the full implications and benefits of this new technology, as well its limitations.

In Vivo Fluoride Ion Detection and Imaging in Mice Using a Designed Near-Infrared Ratiometric Fluorescent Probe Based on IR-780

A ratiometric near-infrared fluorescence probe based on IR-780 is developed and applied to fluoride anion (F^-) detection in potable water and white flour as well as fluorescence imaging in living cells and mice. The proposed probe not only displays a linear ratiometric (F₇₄₀/F₆₉₀ nm) fluorescence response but also possesses near-infrared wavelengths to F^- with a detection limit of 0.2 μM. Moreover, the designed probe displays high selectivity toward F^-, which makes it feasible for F^- detection in potable water and white flour. More importantly, applied to monitor F^- in living HepG2 cells and male BALB/c mice, the probe indicates good biocompatibility and low cytotoxicity. However, no study for F^- detection has been reported by a ratiometric NIR fluorescent probe so far. We expect that this probe with superior properties has great potential for use in F^- detection in biological systems and in vivo studies.

Intraductal Laser Fiber Tip Fracture and Retrieval During Sialendoscopic Laser-Assisted Lithotripsy

Fragmentation of flexible laser fiber tips has been reported to occur during therapeutic bronchoscopy and urologic stone treatment. We report fragmentation of 200-µm single-use silica-based fibers during sialendoscopy-controlled Holmium:YAG laser treatment of a parotid and a submandibular stone. The technique employed to successfully retrieve the fiber tips is described in the context of identifying this potential complication from endoscopic management of sialolithiasis.

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