Mechanism of high velocity jet formation after a gas bubble collapse near the micro fiber immersed in a liquid

Study of methods for controlling direction and velocity of liquid jets formed during subcooled boiling

Objective To investigate the mechanism of stone dusting in Holmium (Ho): YAG laser lithotripsy (LL). Materials and methods Cylindrical BegoStone samples (6 x 6 mm, H x D) were treated in water using a clinical Ho: YAG laser lithotripter in dusting mode (0.2 ~ 0.4 J with 70 ~ 78 s in pulse duration, 20 Hz) at various fiber tip to stone standoff distances (SD = 0, 0.5, and 1 mm). Stone damage craters were quantified by optical coherence tomography and bubble dynamics were captured by high-speed video imaging. To differentiate the contribution of cavitation vs. thermal ablation to stone damage, three additional experiments were performed. First, pre-soaked wet stones were treated in air to assess stone damage without cavitation. Second, the laser fiber was advanced at various offset distances (OSD = 0.25, 1, 2, 3, and 10 mm) from the tip of a flexible ureteroscope to alter the dynamics of bubble collapse. Third, stones were treated with parallel fiber to minimize photothermal damage while isolating the contribution of cavitation to stone damage. Results Treatment in water resulted in 2.5- to 90-fold increase in stone damage compared to those produced in air where thermal ablation dominates. With the fiber tip placed at OSD = 0.25 mm, the collapse of the bubble was distracted away from the stone surface by the ureteroscope tip, leading to significantly reduced stone damage compared to treatment without the scope or with scope at large OSD of 3 ~ 10 mm. The average crater volume produced by parallel fiber orientation at 0.2 J after 100 pulses where cavitation is the dominant mechanism of stone damage was comparable with those produced by using perpendicular fiber orientation within SD = 0.25 ~ 1 mm. Conclusion Cavitation plays a dominant role over photothermal ablation in stone dusting during short pulse Ho: YAG LL.

Cavitation Plays a Vital Role in Stone Dusting during Short Pulse Holmium: YAG Laser Lithotripsy.

This article outlines the current best practice in the management of varicose veins. "Varicose veins" traditionally means bulging veins, usually seen on the legs, when standing. It is now a general term used to describe these bulging veins, and also underlying incompetent veins that reflux and cause the surface varicose veins. Importantly, "varicose veins" is often used for superficial venous reflux even in the absence of visible bulging veins. These can be simply called "hidden varicose veins". Varicose veins usually deteriorate, progressing to discomfort, swollen ankles, skin damage, leg ulcers, superficial venous thrombosis and venous bleeds. Patients with varicose veins and symptoms or signs have a significant advantage in having treatment over conservative treatment with compression stockings or venotropic drugs. Small varicose veins or telangiectasia without symptoms or signs can be treated for cosmetic reasons. However, most have underlying venous reflux from saphenous, perforator or local "feeding veins" and so investigation with venous duplex should be mandatory before treatment. Best practice for investigating leg varicose veins is venous duplex ultrasound in the erect position, performed by a specialist trained in ultrasonography optimally not the doctor who performs the treatment. Pelvic vein reflux is best investigated with transvaginal duplex ultrasound (TVS), performed using the Holdstock-Harrison protocol. In men or women unable to have TVS, venography or cross-sectional imaging is needed. Best practice for treating truncal vein incompetence is endovenous thermal ablation. Increasing evidence suggests that significant incompetent perforating veins should be found and treated by thermal ablation using the transluminal occlusion of perforator (TRLOP) approach, and that incompetent pelvic veins refluxing into symptomatic varicose veins in the genital region or leg should be treated by coil embolisation. Bulging varicosities should be treated by phlebectomy at the time of truncal vein ablation. Monitoring and reporting outcomes is essential for doctors and patients; hence, participation in a venous registry should probably be mandatory. 

/pdf/current-best-practice-in-the-management-of-varicose-veins-1ide3p27.pdf

Current Best Practice in the Management of Varicose Veins

Endovenous laser ablation using laser systems emitting at wavelengths > 1900 nm: a systematic review

Thulium fiber laser with a wavelength of 1.94 µm is widely used in urology for lithotripsy. This paper studies the mechanism of lithotripsy and evaluates its clinical efficiency using the superpulse thulium fiber laser with a wavelength of 1.94 µm and a peak power of 500 W. An experimental setup was developed to study the mechanism of lithotripsy. The superpulse thulium fiber laser (TFL) with a wavelength of 1.94 µm with a peak power of 500 W (FiberLase U2 from “IRE-POLUS” Ltd., Fryazino, Moscow Region, Russia) was used for the lithotripsy of stone phantoms (BegoStone). The processes were recorded with a high-speed camera. The acoustic signals registered during lithotripsy were studied with wideband and needle hydrophones. The main mechanism of lithotripsy performed by using superpulse TFL was thermal cavitation in the water-filled pore space and thermal destruction of the phantom. During the clinical application of the superpulse thulium fiber laser, the high efficiency of laser lithotripsy was established. The performed optical and acoustic studies showed that the mechanism of the destruction of stones was based on the synergic effect of the explosive boiling of water in the pore space of the stone, and its thermal destruction is associated with the heating of the stone to several hundred degrees with laser radiation.

Mechanism of Lithotripsy by Superpulse Thulium Fiber Laser and Its Clinical Efficiency

Heat transfer in water under laser heating through fibres for endovenous laser coagulation

There are considered characteristics of the laser medical devices working at the wavelengths 1.94; 2.01 and 2.1 µm, which are used in urology for surgical operations. It is shown that unlike action in the air environment, section of the biotissue in the water environment (physiological solution) is performed by the steam-gas stream which is formed as a result of superintensive boiling in thin (about 0.1 mm) a liquid layer in which absorbed laser radiation. Coagulation of the biotissue, adjacent to a section, happens due to heat which is produced via vapor condensation.

/pdf/laser-hydrodynamic-biotissue-dissection-in-operative-urology-3bdbnalykk.pdf

Laser hydrodynamic biotissue dissection in operative urology

It is shown that unlike action in the air environment, section of the biotissue in the water environment (physiological solution) is performed by the steam-gas stream which is formed as a result of superintensive boiling in thin (about 0.1 mm) a liquid layer in which absorbed laser radiation. Coagulation of the biotissue, adjacent to a section, happens due to heat which is produced via vapor condensation.
Keywords: laser radiation in urology, a laser enucleation of the BPH, laser removal of the bladder cancer.

/pdf/on-the-difference-in-action-of-the-laser-light-with-4laug4ogmh.pdf

On the Difference in Action of the Laser Light with Wavelength Near 2mm on Biotissue in Gas and Water Media

Investigation results of laser induced blood plasma heating and coagulation are presented. The laser radiation with wavelengths 1.55 and 1.94 μm and fibers with flat end and radial fibers were used. Experiments shown that for radiation of 1.94 μm, heat transfer and plasma coagulation begin at lower power levels comparing to 1.55 μm, and that even with radial emission output, for most of the time heat flows and coagulated particles propagate asymmetric in the vertical plane, mostly upward.

Study of laser radiation blood plasma heating and coagulation

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