Cees W. M. van der Geld

The heat-pipe resembling action of boiling bubbles in endovenous laser ablation

Endovenous laser ablation (EVLA) produces boiling bubbles emerging from pores within the hot fiber tip and traveling over a distal length of about 20xa0mm before condensing. This evaporation-condensation mechanism makes the vein act like a heat pipe, where very efficient heat transport maintains a constant temperature, the saturation temperature of 100°C, over the volume where these non-condensing bubbles exist. During EVLA the above-mentioned observations indicate that a venous cylindrical volume with a length of about 20xa0mm is kept at 100°C. Pullback velocities of a few mm/s then cause at least the upper part of the treated vein wall to remain close to 100°C for a time sufficient to cause irreversible injury. In conclusion, we propose that the mechanism of action of boiling bubbles during EVLA is an efficient heat-pipe resembling way of heating of the vein wall.

Endovenous laser ablation (EVLA): a review of mechanisms, modeling outcomes, and issues for debate

Endovenous laser ablation (EVLA) is a commonly used and very effective minimally invasive therapy to manage leg varicosities. Yet, and despite a clinical history of 16xa0years, no international consensus on a best treatment protocol has been reached so far. Evidence presented in this paper supports the opinion that insufficient knowledge of the underlying physics amongst frequent users could explain this shortcoming. In this review, we will examine the possible modes of action of EVLA, hoping that better understanding of EVLA-related physics stimulates critical appraisal of claims made concerning the efficacy of EVLA devices, and may advance identifying a best possible treatment protocol. Finally, physical arguments are presented to debate on long-standing, but often unfounded, clinical opinions and habits. This includes issues such as (1) the importance of laser power versus the lack of clinical relevance of laser energy (Joule) as used in Joule per centimeter vein length, i.e., in linear endovenous energy density (LEED), and Joule per square centimeter vein wall area, (2) the predicted effectiveness of a higher power and faster pullback velocity, (3) the irrelevance of whether laser light is absorbed by hemoglobin or water, and (4) the effectiveness of reducing the vein diameter during EVLA therapy.

Particle image velocimetry measurements of a steam-driven confined turbulent water jet

In this paper experiments are reported on a condensing steam jet. Superheated steam is injected at the bottom centre of a cylindrical water vessel, resulting in a turbulent jet with Reynolds numbers varying between

Some controversies in endovenous laser ablation of varicose veins addressed by optical-thermal mathematical modeling.

7.9{times}10^4

Irreversible electroporation: Just another form of thermal therapy?

and

The influence of a metal stent on the distribution of thermal energy during irreversible electroporation

18.1{times}10.4

Optical-thermal mathematical model for endovenous laser ablation of varicose veins

, depending on the bulk temperature of the water. Near the steam inlet, the flow is two-phase with rapidly condensing steam. Downstream of a development region the jet is essentially single-phase. Using particle image velocimetry in a vertical plane through the central axis, instantaneous velocity fields of the single-phase region have been measured at a rate of 15Hz. The velocity field in this region is found to be self-similar, i.e. the width of the jet,

Temperature measurements for dose-finding in steam ablation

r_{1/2}

Periocular CO2 laser resurfacing: severe ocular complications from multiple unintentional laser impacts on the protective metal eye shields: OCULAR COMPLICATIONS OF CO2 LASER RESURFACING

, increases linearly with increasing distance to the virtual origin, and a Gaussian profile prevails if velocities and distances are properly scaled. The spreading rate is equal to the one usually found in single-phase jets, and temperature independent. The virtual origin of the jet is positioned at a temperature-dependent distance (3–7 nozzle diameters) upstream of the steam inlet, and this distance is shown to correlate with the length of the condensation region. The turbulence intensity is found to be similar to the intensities usually reported for single-phase jets, although full isotropy is only reached at a distance of 15 nozzle diameters from the nozzle. The jet exhibits a slow wobbling motion, which can be attributed to instability of the backflow resulting from the confinement. When the measurements are compensated for this wobble, a slightly smaller spreading rate is obtained, which indicates that unconditional averaging may conceal significant flow structuring.

Comment to: Månsson C, Nilsson A, Karlson B-M. Severe complications with irreversible electroporation of the pancreas in the presence of a metallic stent: a warning of a procedure that never should be performed. Acta Radiologica Short Reports 2014;3(11):1-3.

Minimally invasive treatment of varicose veins by endovenous laser ablation (EVLA) becomes more and more popular. However, despite significant research efforts performed during the last years, there is still a lack of agreement regarding EVLA mechanisms and therapeutic strategies. The aim of this article is to address some of these controversies by utilizing optical–thermal mathematical modeling. Our model combines Mordons light absorption-based optical–thermal model with the thermal consequences of the thin carbonized blood layer on the laser fiber tip that is heated up to temperatures of around 1,000xa0°C due to the absorption of about 45xa0% of the laser light. Computations were made in MATLAB. Laser wavelengths included were 810, 840, 940, 980, 1,064, 1,320, 1,470, and 1,950xa0nm. We addressed (a) the effect of direct light absorption by the vein wall on temperature behavior, comparing computations by using normal and zero wall absorption; (b) the prediction of the influence of wavelength on the temperature behavior; (c) the effect of the hot carbonized blood layer surrounding the fiber tip on temperature behavior, comparing wall temperatures from using a hot fiber tip and one kept at room temperature; (d) the effect of blood emptying the vein, simulated by reducing the inside vein diameter from 3 down to 0.8xa0mm; (e) the contribution of absorbed light energy to the increase in total energy at the inner vein wall in the time period where the highest inner wall temperature was reached; (f) the effect of laser power and pullback velocity on wall temperature of a 2-mm inner diameter vein, at a power/velocity ratio of 30xa0J/cm at 1,470xa0nm; (g) a comparison of model outcomes and clinical findings of EVLA procedures at 810xa0nm, 11xa0W, and 1.25xa0mm/s, and 1,470xa0nm, 6xa0W, and 1xa0mm/s, respectively. Interestingly, our model predicts that the dominating mechanism for heating up the vein wall is not direct absorption of the laser light by the vein wall but, rather, heat flow to the vein wall and its subsequent temperature increase from two independent heat sources. The first is the exceedingly hot carbonized layer covering the fiber tip; the second is the hot blood surrounding the fiber tip, heated up by direct absorption of the laser light. Both mechanisms are about equally effective for all laser wavelengths. Therefore, our model concurs the finding of Vuylsteke and Mordon (Ann Vasc Surg 26:424–433, 2012) of more circumferential vein wall injury in veins (nearly) devoid of blood, but it does not support their proposed explanation of direct light absorption by the vein wall. Furthermore, EVLA appears to be a more efficient therapy by the combination of higher laser power and faster pullback velocity than by the inverse combination. Our findings suggest that 1,470xa0nm achieves the highest EVLA efficacy compared to the shorter wavelengths at all vein diameters considered. However, 1,950xa0nm of EVLA is more efficacious than 1,470xa0nm albeit only at very small inner vein diameters (smaller than about 1xa0mm, i.e., veins quite devoid of blood). Our model confirms the efficacy of both clinical procedures at 810 and 1,470xa0nm. In conclusion, our model simulations suggest that direct light absorption by the vein wall is relatively unimportant, despite being the supposed mechanism of action of EVLA that drove the introduction of new lasers with different wavelengths. Consequently, the presumed advantage of wavelengths targeting water rather than hemoglobin is flawed. Finally, the model predicts that EVLA therapy may be optimized by using 1,470xa0nm of laser light, emptying of the vein before treatment, and combining a higher laser power with a greater fiber tip pullback velocity.