Endovenous Simulated Laser Experiments at 940 nm and 1470 nm Suggest Wavelength-Independent Temperature Profiles

Endovenous (minimally invasive) procedures for treatment of varicose veins : The gentle and effective alternative to high ligation and stripping operations

Thermal ablation of saphenous vein varicosis has developed into a standard procedure for treatment of varicose veins. The clinical success of the endovenous thermal procedure is comparable to high ligation and stripping operations and a significant difference between these groups could not be detected in long-term analyses. The only difference is in the genesis of saphenofemoral recurrence detected by duplex ultrasound: neoangiogenesis occurs after high ligation and stripping operation and after endovenous ablation of the great saphenous vein a recurrence occurs predominantly via a residual anterior accessory saphenous vein (AASV). Reduction of costs by an increase in endovenous procedures carried out in an outpatient setting in comparison to stripping operations, which are still frequently carried out in Germany (in comparison to other countries) as an inpatient procedure, have meanwhile been confirmed. An endovenous crossectomy (i.e., high ligation) should be strived for. Nonthermal endoluminal catheter procedures are predominantly reserved for treatment of the short saphenous vein.

[Endovenous (minimally invasive) procedures for treatment of varicose veins : The gentle and effective alternative to high ligation and stripping operations]

Thermal ablation of saphenous vein varicosis has developed into a standard procedure for treatment of varicose veins. The clinical success of the endovenous thermal procedure is comparable to high ligation and stripping operations and a significant difference between these groups could not be detected in long-term analyses. The only difference is in the genesis of saphenofemoral recurrence detected by duplex ultrasound: neoangiogenesis occurs after high ligation and stripping operation and after endovenous ablation of the great saphenous vein a recurrence occurs predominantly via a residual anterior accessory saphenous vein (AASV). Reduction of costs by an increase in endovenous procedures carried out in an outpatient setting in comparison to stripping operations, which are still frequently carried out in Germany (in comparison to other countries) as an inpatient procedure, have meanwhile been confirmed. An endovenous crossectomy (i.e. high ligation) should be strived for. Nonthermal endoluminal catheter procedures are predominantly reserved for treatment of the short saphenous vein.

Picosecond Laser-Induced Photothermal Skin Damage Evaluation by Computational Clinical Trial

Background and Objectives

Computational clinical trial (CCT) in the field of laser medicine promotes clinical application of novel laser devices, because this trial carried out based on numerical modeling of laser-tissue interactions and simulation of a series of treatment process. To confirm the feasibility of the computational clinical trial of skin treatment with a novel picosecond laser, this paper presents an evaluation method of the safety.

Study Design/Materials and Methods

In this method, the light propagation and thermal diffusion process after ultrashort light pulse irradiation to a numerical skin model is calculated and the safety based on the photothermal damage is evaluated by computational modeling and simulation. As an example, the safety of a novel picosecond laser device was examined by comparing with several laser devices approved for clinical use.

Results

The ratio of the maximum thermal damage induced by picosecond laser irradiation was 1.2 × 10^-2 % at the epidermis, while that caused by approved laser irradiation was 99 % at the capillary vessels. The numerical simulation demonstrated that less thermal damage was observed compared with the approved devices. The results show the safety simulated by photothermal damage calculation was consistent with the reported clinical trials.

Conclusions

This computational clinical trial shows the feasibility of applying computational clinical trials for the safety evaluation of novel medical laser devices. In contrast to preclinical and clinical tests, the proposed computational method offers regulatory science for appropriately and quickly predicting and evaluating the safety of a novel laser device.

Endovascular laser treatment of incompetent saphenous veins using the 1470 nm diode laser and radial fiber

Objectives

To assess the technical success, complications, and patients' quality of life (QoL) after treatment of chronic venous disease (CVD) using the 1470 nm radial fiber laser.

Methods

A total of 170 patients with chronic venous disease, classified as C2 to C4 according to CEAP classification, were treated for incompetent greater (GSV) and small (SSV) saphenous veins, using the 1470 nm radial fiber laser and application of tumescent anesthesia. Additional phlebectomies were performed through stab microincisions, while 11 patients further underwent sclerotherapy intraoperatively. Patients' QoL was recorded using a CIVIQ-20 questionnaire pre and post-operatively.

Results

Technical success regarding GSV vein occlusion was recorded at 100% and 98% during 12 and 24 month follow up respectively. SSV occlusion rates were recorded at 100% for the same period. 55% of patients were classified as C2. Mean laser application time was 401.1 ± 92.6 s and 169.4 ± 56.8 s, while an average of 3986.6 ± 934.9 and 1643.5 ± 534.1 J were applied during ablation of GSV and SSV respectively. Three incidents of postoperative pain were recorded. Two patients exhibited partial proximal GSV recanalization, while two patients reported mild post-operative temporal paresthesia. No major complications were observed post-operatively. A significant improvement in patients' QoL was demonstrated through the CIVIQ-20 questionnaires. Mean pre-operative CIVIQ-20 total score was recorded at 77 ± 3.9, with a total score of 32.8 ± 2.8 being observed during 12 month follow-up.

Conclusions

Endovascular laser treatment using the 1470 nm radial fiber laser constitutes an effective and safe modality for treatment of CVD.

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Chronic venous disease (CVD) is one of the most commonly encountered health issues regarding venous disorders.

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A paradigm shift has occurred in the 21st century regarding its treatment, offering less invasive treatment options.

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This study was conducted in a series of 170 patients who were treated for CVD the 1470 nm diode laser with radial fiber.

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Technical success rate was excellent with only a few minor incidents of post operative complications.

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Patients' quality of life was drastically improved as it was recorded using a CIVIQ-20 questionnaire.

Endovenous Laser Application

Introduction: Endoluminal vein treatment is a promising minimal invasive treatment option for peoples suffering from varicose veins. The basic mechanism underlying this procedure is to selectively induce heat in the vessel wall with the result of denaturation of proteins and shrinkage of collagen fibers due to energy application. So far energy could be applied either as RF-current, laser light or water steam. The different approaches to deliver such forms of energies are described.

Methods: Investigations on heat dependent vein tissue effects were performed. The degree of shrinkage and wall thickening due to heat induction was calculated. Tensile test on vein tissue were performed. Investigation using the radial emitting laser fibre in the ox-foot-model under reproducible condition were done and wavelengths dependent tissue reaction were explored.

Results: The experiments clearly demonstrate the degree of the shrinkage of length and diameter, the thickening of the vein wall, as well as the decrease of the elasticity of the tissue. The optical irradiation pattern of the radial emitting laser fiber serves for safe and reproducible energy application directly to the vein wall. Using a laser wavelength with high absorption by the tissue water needs reduced irradiation and irradiance compared to wavelengths with less water absorption. Conclusion: An experimental approach to improve laser application for endovenous varicose treatment is described. Laser parameters and treatment parameters were found which are now under clinical testing. The demonstrated tissue effects may help to find further arguments for clinical findings and sensations described by the patients during follow-up.

Real-time temperature monitoring with fiber Bragg grating sensor during diffuser-assisted laser-induced interstitial thermotherapy

High-sensitivity temperature sensors have been used to validate real-time thermal responses in tissue during photothermal treatment. The objective of the current study was to evaluate the feasible application of a fiber Bragg grating (FBG) sensor for diffuser-assisted laser-induced interstitial thermotherapy (LITT) particularly to treat tubular tissue disease. A 600 - ? m core-diameter diffuser was employed to deliver 980-nm laser light for coagulation treatment. Both a thermocouple and a FBG were comparatively tested to evaluate temperature measurements in ex vivo liver tissue. The degree of tissue denaturation was estimated as a function of irradiation times and quantitatively compared with light distribution as well as temperature development. At the closer distance to a heat source, the thermocouple measured up to 41% higher maximum temperature than the FBG sensor did after 120-s irradiation (i.e., 98.7 ° C ± 6.1 ° C for FBG versus 131.0 ° C ± 5.1 ° C for thermocouple; p < 0.001 ). Ex vivo porcine urethra tests confirmed the real-time temperature measurements of the FBG sensor as well as consistently circumferential tissue denaturation after 72-s irradiation ( coagulation thickness = 2.2 ± 0.3 ?? mm ). The implementation of FBG can be a feasible sensing technique to instantaneously monitor the temperature developments during diffuser-assisted LITT for treatment of tubular tissue structure.

Resultados de médio e longo prazo do tratamento endovenoso de varizes com laser de diodo em 1940 nm: análise crítica e considerações técnicas

Contexto

Desde a introdução do laser endovenoso para tratamento das varizes, há uma busca pelo comprimento de onda ideal, capaz de produzir o maior dano seletivo possível com maior segurança e menor incidência de efeitos adversos.

Objetivos

Avaliar os resultados de médio e longo prazo do laser de diodo de 1940 nm no tratamento de varizes, correlacionando os parâmetros utilizados com a durabilidade do desfecho anatômico.

Métodos

Revisão retrospectiva de pacientes diagnosticados com insuficiência venosa crônica em estágio clínico baseado em clínica, etiologia, anatomia e patofisiologia (CEAP) C2 a C6, submetidos ao tratamento termoablativo endovenoso de varizes tronculares, com laser com comprimento de onda em 1940 nm com fibra óptica de emissão radial, no período de abril de 2012 a julho de 2015. Uma revisão sistemática dos registros médicos eletrônicos foi realizada para obter dados demográficos e dados clínicos, incluindo dados de ultrassom dúplex, durante o período de seguimento pós-operatório.

Resultados

A média de idade dos pacientes foi de 53,3 anos; 37 eram mulheres (90,2%). O tempo médio de seguimento foi de 803 dias. O calibre médio das veias tratadas foi de 7,8 mm. A taxa de sucesso imediato foi de 100%, com densidade de energia endovenosa linear (linear endovenous energy density, LEED) média de 45,3 J/cm. A taxa de sucesso tardio foi de 95,1%, com duas recanalizações por volta de 12 meses pós-ablação. Não houve nenhuma recanalização nas veias tratadas com LEED superior a 30 J/cm.

Conclusões

O laser 1940 nm mostrou-se seguro e efetivo, em médio e longo prazo, para os parâmetros propostos, em segmentos venosos com até 10 mm de diâmetro.

Factors affecting optimal linear endovenous energy density for endovenous laser ablation in incompetent lower limb truncal veins – A review of the clinical evidence

Objectives

The objective is to identify the factors that affect the optimal linear endovenous energy density (LEED) to ablate incompetent truncal veins.

Methods

We performed a literature review of clinical studies, which reported truncal vein ablation rates and LEED. A PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analysis) flow diagram documents the search strategy. We analysed 13 clinical papers which fulfilled the criteria to be able to compare results of great saphenous vein occlusion as defined by venous duplex ultrasound, with the LEED used in the treatment.

Results

Evidence suggests that the optimal LEED for endovenous laser ablation of the great saphenous vein is >80 J/cm and <100 J/cm in terms of optimal closure rates with minimal side-effects and complications. Longer wavelengths targeting water might have a lower optimal LEED. A LEED <60 J/cm has reduced efficacy regardless of wavelength. The optimal LEED may vary with vein diameter and may be reduced by using specially shaped fibre tips. Laser delivery technique and type as well as the duration time of energy delivery appear to play a role in determining LEED.

Conclusion

The optimal LEED to ablate an incompetent great saphenous vein appears to be >80 J/cm and <95 J/cm based on current evidence for shorter wavelength lasers. There is evidence that longer wavelength lasers may be effective at LEEDs of <85 J/cm.

Randomized clinical trial of 940- versus 1470-nm endovenous laser ablation for great saphenous vein incompetence

Background

The independent effect of wavelength used for endovenous laser ablation (EVLA) on patient-reported outcomes, health-related quality of life (HRQoL), treatment success and complications has not yet been established in a randomized clinical trial. The aim was to compare two different wavelengths, with identical energy level and laser fibres, in patients undergoing EVLA.

Methods

Patients with great saphenous vein incompetence were randomized to receive 940- or 1470-nm EVLA. The primary outcome was pain at 1 week. Secondary outcomes were: patient satisfaction, duration of analgesia use and time without normal activities assessed at 1 week; HRQoL after 12 weeks; treatment success after 12 and 52 weeks; change in Venous Clinical Severity Score (VCSS) after 12 weeks; and adverse events at 1 and 12 weeks.

Results

A total of 142 legs were randomized (940-nm EVLA, 70; 1470-nm EVLA, 72). Patients in the 1470-nm laser group reported significantly less pain on a visual analogue scale than those in the 940-nm laser group: median (i.q.r.) score 3 (2–7) versus 6 (3–8) (P = 0·004). Duration of analgesia use was significantly shorter after 1470-nm EVLA: median (i.q.r.) 1 (0–3) versus 2 (0–5) days (P = 0·037). HRQoL and VCSS improved equally in both groups. There was no difference in treatment success rates. Complications were comparable in both groups, except for more superficial vein thrombosis 1 week after 1470-nm EVLA.

Conclusion

EVLA using a 1470-nm wavelength fibre was associated with improved postoperative pain and a reduction in analgesia use in the first week after surgery compared with use of a 940-nm fibre. Treatment success and adverse event rates were similar. Registration number: NCT01637181 (http://www.clinicaltrials.gov).

Laser; best practice techniques and evidence

Laser ablation involves the delivery of laser light through a glass fibre placed into the lumen of a refluxing vein. This energy is converted into heat inducing a permanent, non-thrombotic occlusion. This highly effective and safe approach has significant advantages over traditional surgical treatment and has driven the endovenous revolution in the management of varicose veins. This chapter will explore the mechanism of action, present the evidence of laser' clinical and cost effectiveness, and analyse specific and generic aspects of laser ablation technique.

Circumferential irradiation for interstitial coagulation of urethral stricture

An optical diffuser was developed to achieve radially uniform light irradiation by micro-machining helical patterns on the fiber surface for endoscopically treating urethral stricture. Spatial emission from the diffuser was evaluated by goniometric measurements. A computational model was developed to predict spatio-temporal heat distribution during the interstitial coagulation. The fabricated diffuser yielded circumferential light distribution with slightly concentrated energy at the proximal end. Both simulation and tissue testing demonstrated approximately 1-mm coagulation thickness at 6 W for 10 sec with 1470 nm. The proposed optical diffuser may be a feasible tool to treat the urethral stricture in a uniform manner.

Comparing 1470- and 980-nm diode lasers for endovenous ablation treatments

The purpose of this study was to compare the effectiveness of 1470- and 980-nm lasers with regard to power output, complications, recanalization rates, and treatment response. We prospectively evaluated the effectiveness of endovenous laser ablation (EVLA) in a total of 152 great and small saphenous veins from 96 patients. Lasers were randomly used based on the availability of the units. Patients were clinically evaluated for Clinical Etiologic Anatomic Pathophysiologic (CEAP) stage and examined with Doppler ultrasound. Treatment response was determined anatomically by occlusion of the vein and clinically by the change in the venous clinical severity score (VCSS). Seventy-eight of the saphenous veins underwent EVLA with a 980-nm laser and 74 underwent EVLA with a 1470-nm laser. Treatment response was (68) 87.2 % in the 980-nm group and (74) 100 % in the 1470-nm group (p = 0.004). The median VCSS decreased from 4 to 2 in the 980-nm group (p < 0.001) and from 8 to 2 (p < 0.001) in the 1470-nm group. At 1-year follow-up, seven veins treated with 980 nm and two veins treated with 1470 nm were recanalized (p = 0.16); the average linear endovenous energy density (LEED) was 83.9 (r, 55-100) J/cm and 58.5 (r, 45-115) J/cm, respectively (p < 0.001). Postoperative minor complications occurred in 23 (29.4 %) limbs in the 980-nm group and in 19 (25.6 %) limbs of the 1470-nm group (p = 0.73). EVLA with the 1470-nm laser have less energy deposition for occlusion and better treatment response.

Temperature profiles of 980- and 1,470-nm endovenous laser ablation, endovenous radiofrequency ablation and endovenous steam ablation

Endovenous thermal ablation (EVTA) techniques are very effective for the treatment of varicose veins, but their exact working mechanism is still not well documented. The lack of knowledge of mechanistic properties has led to a variety of EVTA protocols and a commercially driven dissemination of new or modified techniques without robust scientific evidence. The aim of this study is to compare temperature profiles of 980-and 1,470-nm endovenous laser ablation (EVLA), segmental radiofrequency ablation (RFA), and endovenous steam ablation (EVSA). In an experimental setting, temperature measurements were performed using thermocouples; raw potato was used to mimic a vein wall. Two laser wavelengths (980 and 1,470 nm) were used with tulip-tip fibers and 1,470 nm also with a radial-emitting fiber. Different powers and pullback speeds were used to achieve fluences of 30, 60, and 90 J/cm. For segmental RFA, 1 cycle of 20 s was analyzed. EVSA was performed with two and three pulses of steam per centimeter. Maximum temperature increase, time span of relevant temperature increase, and area under the curve of the time of relevant temperature increase were measured. In all EVLA settings, temperatures increased and decreased rapidly. High fluence is associated with significantly higher temperatures and increased time span of temperature rise. Temperature profiles of 980- and 1,470-nm EVLA with tulip-tip fibers did not differ significantly. Radial EVLA showed significantly higher maximum temperatures than tulip-tip EVLA. EVSA resulted in mild peak temperatures for longer durations than EVLA. Maximum temperatures with three pulses per centimeter were significantly higher than with two pulses. RFA temperature rises were relatively mild, resulting in a plateau-shaped temperature profile, similar to EVSA. Temperature increase during EVLA is fast with a high-peak temperature for a short time, where EVSA and RFA have longer plateau phases and lower maximum temperatures.

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

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 Mordon's 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 1,000 °C due to the absorption of about 45% of the laser light. Computations were made in MATLAB. Laser wavelengths included were 810, 840, 940, 980, 1,064, 1,320, 1,470, and 1,950 nm. 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 0.8 mm; (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 30 J/cm at 1,470 nm; (g) a comparison of model outcomes and clinical findings of EVLA procedures at 810 nm, 11 W, and 1.25 mm/s, and 1,470 nm, 6 W, and 1 mm/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 1,470 nm achieves the highest EVLA efficacy compared to the shorter wavelengths at all vein diameters considered. However, 1,950 nm of EVLA is more efficacious than 1,470 nm albeit only at very small inner vein diameters (smaller than about 1 mm, i.e., veins quite devoid of blood). Our model confirms the efficacy of both clinical procedures at 810 and 1,470 nm. 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 1,470 nm of laser light, emptying of the vein before treatment, and combining a higher laser power with a greater fiber tip pullback velocity.

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

Endovenous laser ablation (EVLA) is successfully used to treat varicose veins. However, the exact working mechanism is still not fully identified and the clinical procedure is not yet standardized. Mathematical modeling of EVLA could strongly improve our understanding of the influence of the various EVLA processes. The aim of this study is to combine Mordon's optical-thermal model with the presence of a strongly absorbing carbonized blood layer on the fiber tip. The model anatomy includes a cylindrically symmetric blood vessel surrounded by an infinite homogenous perivenous tissue. The optical fiber is located in the center of the vessel and is withdrawn with a pullback velocity. The fiber tip includes a small layer of strongly absorbing material, representing the layer of carbonized blood, which absorbs 45% of the emitted laser power. Heat transfer due to boiling bubbles is taken into account by increasing the heat conduction coefficient by a factor of 200 for temperatures above 95 °C. The temperature distribution in the blood, vessel wall, and surrounding medium is calculated from a numerical solution of the bioheat equation. The simulations were performed in MATLAB™ and validated with the aid of an analytical solution. The simulations showed, first, that laser wavelength did virtually not influence the simulated temperature profiles in blood and vessel wall, and, second, that temperatures of the carbonized blood layer varied slightly, from 952 to 1,104 °C. Our improved mathematical optical-thermal EVLA model confirmed previous predictions and experimental outcomes that laser wavelength is not an important EVLA parameter and that the fiber tip reaches exceedingly high temperatures.