Laser-induced Thermal Damage Research Articles

Comparative analysis of thermal damage to laser-irradiated breast tumor based on Fourier conduction and non-Fourier heat conduction models: A numerical study

In recent decades, laser technology has been widely used in surgeries and thermal therapies. To ensure patient safety and enhance therapeutic effectiveness in laser applications, it is crucial to accurately analyze burn injuries during the treatment process. In this study, a bioheat transfer model that includes the effects of metabolic heat generation, capillary blood vessels, and relaxation times of heat flux and temperature gradient was developed to study the non-Fourier heat conduction behavior in 2-D spherical breast tumor during the laser hyperthermia process. By employing different heat conduction models and the Arrhenius burn integration, the temperature distribution and laser-induced thermal damage to tumors were obtained. The progression of burn injury in time and the effect of various parameters on it were investigated. It was observed that the DPL model provides more reliable results in comparison with the CV model in predicting thermal damage to bio-tissue when non-Fourier effects are taken into consideration. The results showed that increasing heat flux phase lag leads to severe thermal damage, earlier onset of empyrosis, and wider and deeper burn injury. However, a greater phase lag of temperature gradient results in lower and superficial thermal damage, milder burn, later onset of empyrosis, and smaller burned area. The effect of laser power density on the onset time of different degrees of burn and their sensitivity to input power were investigated, and the results were represented graphically. Finally, investigation of wave propagation in various tissues revealed that the wave propagation speed is not constant and reduces as time increases.

Investigation of thermal damage in continuous wave laser-induced nanowelding

Continuous wave (CW) laser-induced nanowelding holds great promise in micro-and nano-devices. However, because of the lengthy irradiation duration, the heat effect from CW laser irradiation may harm the manufactured devices. The simulation results show that an increase in irradiation duration will slightly improve the welding temperature but greatly expand the heat-affected area when the irradiation time exceeds 100 ms. Experimental results confirm that Cu nanowires irradiated for 20 ms are slightly oxidized. As the irradiation period is increased to 10,000 ms, the oxygen concentration in Cu nanowires significantly increases, and the color of Cu nanowires becomes first black, then green. The electrical property of the oxidized Cu-Au nanojunction shifts from ohmic contact to Schottky contact. Furthermore, the large heat-affected area will weaken the adhesion between the Au pad and the substrate due to the large difference in thermal expansion coefficient between the metal film and the insulating layer. Consequently, CW laser-induced thermal damage not only impairs the electrical properties of nanostructures but also their reliability.

Numerical and Experimental Study on Thermal Damage Induced by Medium—Infrared Laser

We studied the laser-induced thermal damage on the surface of a single crystal silicon mirror illuminated by a mid-infrared intense laser. We used mid−infrared quasi-continuous wave lasers to irradiate the surface of the single−crystal silicon mirror. The power density of the irradiation process is 1 kW/cm2 to 17 kW/cm2, and the transient temperature field and thermal stress field under different laser fluxes were obtained. The simulation results show that we can calculate the thermal stress and temperature under laser irradiation. In addition, irradiance exceeding the corresponding breaking strength and melting point limit was obtained by the model. We can predict the irradiance that causes cracking and melting. There is little difference between experimental results and simulation results. On this basis, the thermal damage to the surface of the silicon wafer caused by continuous mid−infrared laser irradiation was studied.

Effects of water cooling on laser-induced thermal damage in rat hepatectomy.

PurposeHigh‐powered lasers are commonly used for tissue resection in surgeries, including liver resection, medically known as hepatectomy; however, such lasers inevitably induce thermal damage that causes postoperative complications. This study aims to explore the effects of water cooling and different laser output modes on laser‐induced thermal damage during hepatectomy.MethodsTo avoid the influence of superposition, a 980‐nm diode laser was used for a single‐point hepatectomy. Eighteen Sprague–Dawley rats were used to explore the effects of water cooling and different laser output modes. A constant energy 10‐J laser was used to cut the liver tissue with a power of 10 W and time of 1 second. The rats were randomly divided into six groups. The first three groups were assigned as test subjects for different laser output modes. Group 1 was operated with a continuous laser output for a duration of 1 second. Groups 2 and 3 were operated with a pulsed laser output for a duration of 1 second and a pulse width of 0.5 and 0.25 seconds, respectively. Groups 4, 5, and 6 were assigned for the water cooling test. Water cooling was performed based on the parameters of the first three groups. Medical saline (0.9% NaCl) was used for water cooling. The main observation indicators were resection efficiency and thermal damage, including the area of the thermal damage zone. Resection efficiency is calculated by dividing the resection area by the total thermal damage area.ResultsIn the three water cooling groups, the area of the resection, carbonized, sub‐boiling coagulated, and total thermal damage zones were 0.0677, 0.00, 1.7293, and 2.2982 mm2 in Group 4; 0.0465, 0.00, 1.3205, and 1.8414 mm2 in Group 5; and 0.0565, 0.00, 1.4301, and 1.9650 mm2 in Group 6, respectively. Compared with the first three groups, the water cooling groups exhibited significantly reduced thermal damage areas of in the carbonized, sub‐boiling coagulated, and total thermal damage zones (p < 0.001 for all). In addition, there was no statistical difference in the resection area, vacuolated area, and resection efficiency. Furthermore, there was no statistical difference in the area of each thermal damage zone between the continuous and pulsed output groups. The resection efficiencies were 4.82%, 3.34%, 3.73%, 3.93%, 3.36%, and 3.01% in Groups 1 to 6, respectively. Moreover, there was no statistical difference (p > 0.05) in the resection efficiencies.ConclusionWater cooling can reduce the total laser‐induced thermal damage area and prevent tissue carbonization. Therefore, this cooling method can be used as a simple and safe strategy for controlling thermal damage during hepatectomy.

Prediction of In Vivo Laser-Induced Thermal Damage with Hyperspectral Imaging Using Deep Learning.

Thermal ablation is an acceptable alternative treatment for primary liver cancer, of which laser ablation (LA) is one of the least invasive approaches, especially for tumors in high-risk locations. Precise control of the LA effect is required to safely destroy the tumor. Although temperature imaging techniques provide an indirect measurement of the thermal damage, a degree of uncertainty remains about the treatment effect. Optical techniques are currently emerging as tools to directly assess tissue thermal damage. Among them, hyperspectral imaging (HSI) has shown promising results in image-guided surgery and in the thermal ablation field. The highly informative data provided by HSI, associated with deep learning, enable the implementation of non-invasive prediction models to be used intraoperatively. Here we show a novel paradigm “peak temperature prediction model” (PTPM), convolutional neural network (CNN)-based, trained with HSI and infrared imaging to predict LA-induced damage in the liver. The PTPM demonstrated an optimal agreement with tissue damage classification providing a consistent threshold (50.6 ± 1.5 °C) for the damage margins with high accuracy (~0.90). The high correlation with the histology score (r = 0.9085) and the comparison with the measured peak temperature confirmed that PTPM preserves temperature information accordingly with the histopathological assessment.

Hyperspectral Imagery for Assessing Laser-Induced Thermal State Change in Liver.

This work presents the potential of hyperspectral imaging (HSI) to monitor the thermal outcome of laser ablation therapy used for minimally invasive tumor removal. Our main goal is the establishment of indicators of the thermal damage of living tissues, which can be used to assess the effect of the procedure. These indicators rely on the spectral variation of temperature-dependent tissue chromophores, i.e., oxyhemoglobin, deoxyhemoglobin, methemoglobin, and water. Laser treatment was performed at specific temperature thresholds (from 60 to 110 °C) on in-vivo animal liver and was assessed with a hyperspectral camera (500–995 nm) during and after the treatment. The indicators were extracted from the hyperspectral images after the following processing steps: the breathing motion compensation and the spectral and spatial filtering, the selection of spectral bands corresponding to specific tissue chromophores, and the analysis of the areas under the curves for each spectral band. Results show that properly combining spectral information related to deoxyhemoglobin, methemoglobin, lipids, and water allows for the segmenting of different zones of the laser-induced thermal damage. This preliminary investigation provides indicators for describing the thermal state of the liver, which can be employed in the future as clinical endpoints of the procedure outcome.

Identification of the main factors in the 3-D simulation of laser-induced thermal damage in choroidal melanomas

Computational numerical simulation is a valuable tool for studying processes that involve living tissues, since it is not invasive, safer, and cheaper than in vivo experiments. The study of heat transfer within human eyes raises special interest given the numerous existing treatments that involve exposing the eye to external heat sources. Furthermore, there is not much blood flow in most tissues of the eye, which means there is a limited cooling effect and a higher chance of severe thermal damage. Choroidal melanomas are malignant ocular tumors that arise in the choroid, that can be treated by a variety of thermal procedures, among other techniques. Transpupillary thermotherapy (TTT) is one of these treatments, which consists of irradiating the tumor with diode laser, thus heating the tumor within a specific temperature range. In our previous studies, the influence of some parameters on the temperature and thermal damage within the human eye following TTT treatment was studied– the parameters were Vitreous Humor (VH) viscosity, laser output power, and the size of the tumor. Since the data available that are needed for mathematical modeling are scarce and uncertain, the quality of the results was also uncertain. In this study, the main goal was to perform sensitivity analyses to identify which thermal-physical properties significantly influence the results of simulations. A 3-D model of the human eye with a small choroidal melanoma was used. The Navier-Stokes equations were included to consider natural convection inside the VH. A numerical strategy was used to represent tumor shrinkage due to thermal damage. A fractional factorial design of experiments was adopted, and the results were analyzed by building ANOVA (analysis of variance) tables for each case. Our results indicate that the radiation absorption coefficient for the tumor and for the choroid are the only parameters that significantly influence the results among those analyzed ones. This suggests that the uncertainties of most thermophysical properties do not substantially harm the predictions of the simulations. Also, this reinforces that the level of melanin on the tumor should be carefully assessed in order to decide the treatment protocol, since this level is directly related to the absorption coefficient.

Assessment of laser-induced thermal damage in fresh skin with ex vivo confocal microscopy

Laser-induced thermal damage is conventionally assessed using hematoxylin-eosin or nitrotetrazolium blue histology. 1 Ha L. Jaspan M. Welford D. et al. First assessment of a carbon monoxide laser and a thulium fiber laser for fractional ablation of skin. Lasers Surg Med. 2020; (Published online January 14, 2020)https://doi.org/10.1002/lsm.23215 Crossref PubMed Scopus (12) Google Scholar This tissue processing introduces artifacts that may adversely affect image interpretation.

The characterization of laser-induced thermal damage mechanism of mid-infrared optical coatings with surface contaminants

Understanding the laser-induced thermal damage mechanism is important to the development of high power continuous wave (CW) laser. In this paper, we monitor the evolution of damage via a self-build optical element testing platform and build a correspond theoretical model based on the temperature field and heat conduction theory. The waveband of optical coatings (ZnSe and YbF3) under test is dedicated for the mid-infrared. Using a 10 kW level mid-infrared CW laser, the thermal stress damage process of the optical coatings caused by surface contaminants is recorded. The Finite Element Method was employed to calculate the thermal damage mechanism of mid-infrared optical coatings. The calculated thermal damage mechanism agrees very well with our experiment. To the best of our knowledge, this is the first comprehensive study on thermal damage mechanism of mid-infrared coatings with surface contaminants induced by CW laser.

Prediction of laser-induced thermal damage with artificial neural networks

Laser-induced thermotherapy (LITT) has been widely studied since it is a minimally invasive technique for focal destruction of liver tumors without side effects. However, there are still some concerns about the treatment and monitoring thermal effects during operation. Although real-time imaging modalities are available, like magnetic resonance imaging, they are not cost-effective and not applicable to all conditions. This paper presents artificial neural network (ANN) modeling of laser-induced thermal damages on ex vivo liver tissue. In this work three laser sources, i.e. a diode pumped laser with a wavelength of 980 nm, a 1070 nm yttrium lithium fluoride fiber laser, and a 1940 nm thulium fiber laser, were used in order to thermally damage tissues by applying the laser until coagulation observed. The diameter and depth of coagulation were empirically measured and used to train the ANN model by finding the correlation between laser parameters (application time, power, penetration depth, wavelength, and spot size) and thermal damages. Thermal damage can be determined by observing coagulation diameter and coagulation depth. The prediction ability and accuracy of the trained ANN model were tested by comparing the actual and simulated results. Our result showed that the ANN successfully predicts LITT damage in terms of coagulation diameter and coagulation depth, with a very high accuracy. The trained ANN model was compared with two mathematical models. In terms of performance, the ANN is a very useful and practical tool for determining LITT damage.

Influence of surface cracks on laser-induced thermal damage characteristics of optical material

A thermal damage analysis model of fused silica material with surface crack is established. The distributions of modulated light and temperature field on the optical surface are calculated based on FDTD method. According to the surface temperature distribution, the thermal damage thresholds of materials with different crack scales are analyzed. Furthermore, the variations of the damage thresholds caused by surface cracks with two typical morphologies are compared. Results show that the lengths of the cracks have little effect on the damage threshold. On the contrary, it decreases obviously with the increasing of crack width and depth. In addition, the cracks with sharp rectangular shape are more likely to cause material damage due to the stronger modulation of light field.

The influence of the vitreous humor viscosity during laser-induced thermal damage in choroidal melanomas

The study of heat transfer within the human eye is of utmost importance due to the wide variety of existing treatments commonly given by the aid of devices which expose the eye to external heat sources. Also, the ocular tissues are very sensitive to incident radiation, which is focused by the lens in a small area of the retina. Damage may be often intense because of the lack of blood flow in this region and the limited cooling effect. The transpupillary thermotherapy (TTT) is a laser treatment used to treat choroidal melanomas – malignant ocular tumors that arise from the choroid. In the present work, a 3-D computational model of the eye was created to simulate treatments of two different choroidal melanomas. The goal was to calculate the heat transfer and the thermal damage during TTT. Eight models were studied to determine the influence of the Vitreous Humor (VH) viscosity, the laser output power, and the tumor size following the treatment. The models included the Navier-Stokes equations to consider natural convection inside the VH since the VH's viscosity may decrease with age. A numerical strategy was used to represent tumor shrinkage due to thermal damage. The results showed that the liquefied VH presented natural convection, and dramatically reduced the thermal damage in a small tumor (Eye Model 2) from 26.15% to 1.40%, after 60 s of TTT application. Large tumors (Eye Model 1) also presented less tissue destruction in the presence of liquefied VH. However, large tumors do not respond well to TTT, even with normal VH viscosity, as in both cases less than 1% volume of the tumor is damaged after 60 s (s) of exposure time to an infrared continuous diode laser. Our results suggested that in patients with advanced age and liquefied vitreous humor, treatments choices such as TTT should be more carefully considered since it can be less effective due to the laser induced natural convection inside the VH.

Laser-Induced Thermal Damage Simulations of Optical Coatings Due to Intercoupling of Defect and Organic Contamination

The coupling model of defect and organic contamination was presented to analyze the coupling effects on laser-induced damage and understand the damage degradation mechanism of optical films in a closed vacuum environment. The distributions of temperature rise around an absorbing defect in multilayer ZrO2/SiO2 films were computed based on the finite-element simulation. Laser induced damage tests were made to compare with the theoretical model. Test results were in an agreement with the presented model and calculated results of a temperature rise.

MoS2-clad microfibre laser delivering conventional, dispersion-managed and dissipative solitons.

Molybdenum disulfide (MoS2), whose monolayer possesses a direct band gap, displays promising applications in optoelectronics, photonics, and lasers. Recent researches have demonstrated that MoS2 has not only a significant broadband saturable absorption performance, but also a higher optical nonlinear response than graphene. However, MoS2 shows much lower optical damage threshold owing to the poorer thermal conductivity and mechanical property. Here, we exploit a MoS2-clad microfibre (MCM) as the saturable absorber (SA) for the generation of ultrashort pulses under different dispersion conditions. The improved evanescent field interaction scheme can overcome the laser-induced thermal damage, as well as take full advantage of the strong nonlinear effect of MoS2. With the MCM SA, conventional, dispersion-managed, and dissipative solitons are generated around 1600 nm in Er-doped fibre lasers with anomalous, near-zero, and normal cavity dispersions, respectively. Our work paves the way for applications of 2D layered materials in photonics, especially in laser sources.

材料表面缺陷对激光热损伤的影响

材料表面缺陷对激光热损伤的影响

Evolution of the microstructure, mechanical properties, and high-order modal characteristics of AISI 1045 steel subjected to a simulative environment of surface grinding burn

The thermal damage of AISI 1045 steel induced by laser surface treatment (LST), which is used to simulate the surface grinding burn, was comprehensively studied in this paper. By experimental investigation, a deep analysis was performed on the microstructure, hardness, and residual stress of the AISI 1045 steel specimens subjected to the LST process. Furthermore, the high-order modal characteristics of the AISI 1045 steel specimen were studied based on the high-frequency vibrator system. The experimental results reveal that the phase transformation-induced microstructure change, which can be reflected by hardness value, can be regarded as essential of the laser-induced thermal damage. The large tensile residual stress is another inevitable product that resulted from the LST process, which can be used to define the degree of surface grinding burn and belongs to the nondestructive classification technology for surface grinding burn by comparing with the microstructure-based classification technology. Moreover, the strain mode is more sensitive to the thermal damage of the specimen than the displacement mode and the resonant frequency, and the significant strain mode change of the specimen before and after the LST process will occur at higher vibration frequency. The findings confirm that the degree of surface grinding burn can be classified by using the X-ray diffraction (XRD) method, and the thermal damage in surface grinding process can be detected by using both the XRD method and the high-order strain mode method.

Experimental and Theoretical Investigation of Pump Laser Induced Thermal Damage for Polycrystalline Ceramic and Crystal Nd:YAG

Continuous wave 808-nm pump laser induced thermal damage of polycrystalline ceramic and crystalline Nd:YAG materials were investigated both experimentally and theoretically in this paper. The measured temperature agrees well with the theoretical simulation and the maximum hoop stress occurs on the incident facet of the end pumped rod at about √2 times of the pump beam radius w <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> , where the temperature gradient is the highest and the damage occurs first. The pumping laser power makes no influence on the maximum hoop stress location, when the position of the laser beam is unchanged. The thermal damage investigation indicates that the transparent ceramic Nd:YAG has greater resistance than thermal fracture and it is 64% higher than that of the crystals.

Comparison of laser induced thermal fracture between polycrystalline ceramic and crystal Nd:YAG

Continuous wave 808 nm pump laser-induced thermal damage of polycrystalline transparent ceramic and crystalline Nd:YAG materials was investigated both experimentally and theoretically. The measured temperature agrees well with the theoretical simulation, and the maximum hoop stresses occur on the incident facet of the end-pumped rod at about √2 times of the pump beam radius w0, where the temperature gradient is the highest and the damage occurs first at this location. The fracture-limited laser intensity of ceramics was experimentally measured to be 6.4±0.6 kW/cm2, nearly 64% higher than that of the crystals (3.9±0.3 kW/cm2). The deduced thermal fracture stress for ceramic was 386±50 MPa, which is 64% higher than that of the crystals (235±16 MPa).

Laser-induced thermal damage detection in metallic materials via acoustic emission and ensemble empirical mode decomposition

A detection method of laser-induced thermal damage–surface burn, rehardening and residual stress, was studied in this work. Artificial thermal damage was produced to various steels, e.g., AISI 1045, ASTM A36 and AISI 304, by virtue of laser irradiation. The aim of the present work is to identify thermal damage through sensor and feature extraction techniques. Acoustic emission(AE) sensor and ensemble empirical mode decomposition(EEMD) method were employed for this purpose. A de-noising method was proposed to eliminate noises from original AE signals, based on EEMD. Quantified thermal damage features were obtained. Results evidenced a strong correlation between AE features, i.e., RMS value of the reconstructed acoustic emission signal, and surface burn, residual stress value, as well as hardness of steels. The present work could be used as a potential and indirect approach for thermal damage detection.

Hyperthermia sensitizes pigmented cells to laser damage without changing threshold damage temperature

We studied the efficacy of mild hyperthermia as a protective measure against subsequent laser-induced thermal damage. Using a well established in vitro retinal model for laser bioeffects, consisting of an artificially pigmented human retinal pigment epithelial (RPE) cell culture (hTERT-RPE1), we found both protection and sensitization to laser damage that depended upon the location of pigment granules during the hyperthermia preconditioning (PC). Photothermal challenge of cell monolayers consisted of 16 independent replicate exposures of 65 W/cm2 at 514 nm and post laser damage was assessed using fluorescence indicator dyes. Untreated cells had 44% damage, but when melanosome particles (MPs) were intracellular or extracellular during the hyperthermia treatment, laser-induced cell damage occurred 94% or 25% of the time, respectively. Using a recently published method called microthermography, we found that the hyperthermia pretreatment did not alter the threshold temperature for cell death, indicating an alteration in absorption or localization of heat as the mechanism for sensitization and protection. Raman microspectroscopy revealed significant chemical changes in MPs when they were preconditioned within the cytoplasm of cells. Our results suggest intracellular pigment granules undergo chemical modifications during mild hyperthermia that can profoundly affect absorption or heat dissipation.