A parametric study of thermal therapy of skin tissue

Three-dimensional numerical evaluation of skin surface thermal contrast by application of hypothermia at different depths and sizes of the breast tumor

BACKGROUND AND OBJECTIVE

Thermal procedures can provide improvements in the thermal contrast of thermographic images in an attempt to diagnose early cases of breast cancer. This work aims to analyze the thermal contrast of different stages and depths of breast tumors from hypothermia treatment using an active thermography analysis. The influence of variation in metabolic heat generation and adipose tissue composition on thermal contrasts is also analyzed.

METHODS

The proposed methodology was based on the solution of the Pennes equation for a three-dimensional model similar to the real anatomy of the breast by commercial software COMSOL Multiphysics. The thermal procedure consists of three steps: Stationary, hypothermia and thermal recovery. During hypothermia, the boundary condition of the external surface was replaced by a constant temperature of 0, 5, 10, and 15 ^∘C, simulating a gel pack, for cooling times of up to 20 min. In the thermal recovery, after the removal of the cooling, the breast was submitted again to the condition of natural convection on the external surface.

RESULTS

Thermal contrasts in superficial tumors, for all hypothermia resulted in improvements in thermographs. For smallest tumor, the use of high resolution and sensitive thermal imaging cameras to acquire this thermal change may be necessary. For tumor of diameter of 10 cm, cooling from 0 ^∘C can increase the thermal contrast by up to 136% compared to the passive thermography. Analyzes with deeper tumors showed very small temperature variations. Even so, the thermal contrast gain in cooling at 0 ^∘C for the tumor with a diameter of 1 cm reached 37% in relation to passive thermography.

CONCLUSIONS

Thus, this work contributes as an important tool in the analysis of the appropriate use of hypothermia for different cases in early stages of breast cancer, considering that long times are needed to obtain the best thermal contrast.

Heat transfer analysis for tissue with surface heat flux based on the non-linearized form of the three-phase-lag model

The three-phase-lag model of heat conduction has been proposed for considering thermoelastic effect in medium. The bioheat transfer equations based on Taylor's series approximation of the three-phase-lag model were derived in conjunction with a modified energy conservation equation. For exploring the effect of non-linear expansion in the phase lag times, the Taylor's series of second-order expansion was applied. The resulting equation involves mixed derivative terms and higher-order derivatives of temperature with respect to time. The hybrid application of the Laplace transform method and a modified discretization technique was extended to solve the equations and explore the effect of thermoelasticity on the thermal behavior in living tissue with surface heat flux. The influence of thermoelastic parameters and phase lags on heat transfer in tissue has been investigated. The present results illustrate the thermal response oscillation is excited in medium for the thermoelastic effect, the phase lag times significantly affect the amplitude and frequency of the oscillation, and the expansion order of TPL model evidently affects the predicted temperature.

The effect of heat flux distribution and internal heat generation on the thermal damage in multilayer tissue in thermotherapy

Proper analysis of the temperature distribution during heat therapy in the target tissue and around it will prevent damage to other adjacent healthy cells. In this study, the exact solution of steady and unsteady of the hyperbolic bioheat equations is performed for multilayer skin with tumor at different heat fluxes on its surface and the generation of internal heat in the tumor. By determining the temperature distribution in three modes of constant heat flux, parabolic heat flux and internal heat generation in tumor tissue, the amount of burn in all three modes is evaluated. The results indicated that the Fourier or non-Fourier behavior of tissue has no role in the rate of burns in thermotherapy processes. At equal powers applied to the tissue, the internal heat generation in the tumor, constant flux and parabolic flux on the skin surface have the most uniform and most non-uniform temperature distribution, respectively and cause the least and the most thermal damage in the tissue.

Theoretical analysis on thermal treatment of skin with repetitive pulses

Thermal ablation is an efficient method of medical treatment, such as cancer therapy, wound closure, laser cutting, freckle removal and other treatments. In order to guarantee the curative effect and the safety of the patients, the thermal response of the tissue which is subjected to the heat source need to be carefully monitored. However, it is too difficult to achieve real-time monitoring on the full-field temperature. In the present study, efforts were made to build up a theoretical model for the prediction of the thermal response in the human skin. The Dual-Phase-Lag (DPL) bio-heat transfer model and the Henrique’s burn assessment model were employed to describe the interaction of multi-pulse heat source and the skin. The repeated multi-pulse laser is a common heat source in the thermal treatment and the thermal responses of the skin would be complicated under the common effects of the non-Fourier effects and the multi-pulse source. The Green’s function approach was used to solve the governing equations analytically. The closed-form solution for the temperature distribution of the skin was obtained and the thermal damage was estimated based on the temperature results. The influences of the biological parameters (the phase lags of the heat flux and the temperature gradient) and the heat source parameters (the pulse number and the duty ratio) on the temperature distribution, the burn degree and the irreversible burn depth of the irradiated region were discussed.

Numerical analysis of non-Fourier thermal response of lung tissue based on experimental data with application in laser therapy

BACKGROUND AND OBJECTIVE

The thermal therapy is a minimally invasive technique used as an alternative approach to conventional cancer treatments. There is an increasing concern about the accuracy of the thermal simulation during the process of tumor ablation. This study is aimed at investigating the effect of finite speed of heat propagation in the biological lung tissue, experimentally and numerically.

METHODS

In the experimental study, a boundary heat flux is applied to the lung tissue specimens and the temperature variation is measured during a transient heat transfer procedure. In the numerical study, a code is developed based on the finite volume method to solve the classical bio-heat transfer, the Cattaneo and Vernotte, and the Dual-phase-lag (DPL) equations. The thermal response of tissue during the experiments is compared with the predictions of the three heat transfer models.

RESULTS

It is found that the trend of temperature variation by the DPL model resembles the experimental results. The experimental observation in parallel with the numerical results reveals that the accumulated thermal energy diffuses to the surrounding tissue with a slower rate in comparison with the conventional bio-heat transfer model. The DPL model is implemented to study the temperature elevation in the laser irradiation to lung tissue in the presence of gold nanoparticles (GNPs). It is concluded that the extent of the necrotic tumoral region and the area of the damaged healthy tissue are reduced, when the non-Fourier heat transfer is taken into account.

CONCLUSIONS

Results show that considering the phase lags is crucial in planning for an effective thermal treatment, in which the cancerous tissue is ablated and the surrounding tissues are preserved from irreversible thermal damage.

Bio-heat response of skin tissue based on three-phase-lag model

In this article, the thermal response of skin tissue is investigated based on three-phase-lag (TPL) model of heat conduction. The governing equation of bio-heat conduction is established by introducing both the TPL model of heat conduction and a modified energy conservation equation. The analytical solution is obtained by adopting the method of separation of variables and a parametric study on temperature responses in TPL model is carried out. It is shown that the TPL model can predict both the diffusion and wave characteristics of bio-heat conduction. Increasing the phase-lag of thermal displacement gradient would result in the rise of thermal propagation speed and decrease the temperature in affected zone. The perfusion rate of arterial blood has no obvious effect on thermal propagation velocity and thermal propagation lagging. Increasing of the rate of blood perfusion contributes to decreasing the temperature of steady state.

Thermal Analysis of Infrared Irradiation-Assisted Nanosecond-Pulsed Tumor Ablation

Nanosecond Pulsed Electric Fields (nsPEF) have the potential to treat a variety of cancer types including melanoma, pancreatic and lung squamous cancers. Recent studies show that nsPEF-based cancer therapy may be improved further with the assistance of moderate heating of the target. A feedback-looped heating system, utilizing a 980-nm fiber optic laser, was integrated into nsPEF electrodes for tumor ablation. The laser beam profile was determined to be Gaussian using a knife-edge technique. Thermal properties of the biological target were evaluated based on the treatment area, penetration depth and thermal distribution due to laser irradiation with or without nsPEF. Synergistic effects between nsPEF and the moderately elevated temperature at the target was observed, resulting in enhanced overall survival tumor regression up to 50% in the treatment of lung squamous cell cancer in mice.

Thermal damage in three-dimensional vivo bio-tissues induced by moving heat sources in laser therapy

The thermal damage of a three-dimensional bio-tissue model irradiated by a movable laser beam was studied in this work. By employing the DPL biological heat conduction model and Henriques' thermal damage assessment model, the distribution of burn damage of vivo human tissue during laser therapy was analytically obtained. The influences of laser moving velocity, laser spot size, phase lags of heat flux and temperature gradient were discussed. It was found that the laser moving speed and the laser spot size greatly influence the thermal damage degree by affecting the energy concentration degree. The increases of the laser moving speed and laser spot size can enlarge the irradiated region and reduce the burn degree. A greater phase lag of temperature gradient led to lower accumulation of thermal energy and lower burn degree. However, the increment of heat flux phase lag leads to the thermal energy accumulation and more serious burn degree in the irradiated region.

Theoretical analysis of nanoshell-assisted thermal treatment for subcutaneous tumor

The hyperthermia is an efficient technique for tumor treatment, in which the tumor is subjected to a heating source, such as laser, supersonic or electromagnetic field. In order to improve the therapeutic efficiency and to protect the surrounding healthy tissues, gold nanoshells are embedded in the tumor as the additive to make it absorb more thermal energy than the healthy tissues. In the present study, a one-dimensional three-layered model is established to investigate the thermal response of the bio-tissue in the hyperthermia treatment for subcutaneous tumor. The governing equations are solved analytically by using the Green's function method and the Henriques' model is employed to evaluate the degree of thermal damage in the target tissue. The influences of the volumetric density of gold nanoshells on the temperature distribution and thermal damage are discussed in detail. When the gold nanoshells are embedded with a proper density, it can improve the efficiency of tumor killing and protecting the subcutaneous tissue from being burnt. The closed-form solution for the governing equations in multilayered tissues can be a theoretical guideline to selection of appropriate parameters of the gold nanoshells.