Analytical and numerical analysis of the dual-pulse lag heat transfer in a three-dimensional tissue subjected to a moving multi-point laser beam.

An extensive algorithm based on both analytical and numerical solution methodologies is proposed to obtain transient temperature distributions in a three-dimensional living tissue subjected to a moving single-point and multi-point laser beam by considering metabolic heat generation and blood perfusion rate. Here, the dual-phase lag/Pennes equation is analytically solved by using the method of Fourier series and the Laplace transform. The ability to model single-point or multi-point laser beams as an arbitrary function of place and time is a significant advantage of the proposed analytical approach, which can be used to solve similar heat transfer problems in other living tissues. Besides, the related heat conduction problem is numerically solved based on the finite element method. The effects of laser beam transitional speed, laser power, and the number of laser points on the temperature distribution within the skin tissue are investigated. Moreover, the temperature distribution predicted by the dual-phase lag model is compared with that of the Pennes model under different working conditions. For the studied cases, it is observed that the maximum tissue temperature decreased about 63% by an increase of 6mm/s in the speed of the laser beam. An increase in the laser power from 0.8W/cm3 to 1.2W/cm3 results in a 28 °C increase in the maximum temperature of the skin tissue. It is observed that the maximum temperature predicted by the dual-phase lag model is always lower than that of the Pennes model and the temperature variations over time are sharper, while their results are entirely consistent over the simulation time. The obtained numerical results indicated that the dual-phase lag model is preferred in heating processes occurring at short intervals. Among the investigated parameters, the laser beam speed has the most considerable effect on the difference between the results of the Pennes and the dual-phase lag models.

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.

Designing suitable shoes to prevent foot frostbite through optimization of the geometric dimensions of the shoe and sock model.

To prevent frostbite in cold environments, proper dimensions and materials for different parts of shoes along with the optimal design of shoe geometry were investigated. Furthermore, the optimal geometry of shoes was computed using an optimization algorithm to provide maximum thermal protection for the foot while having the lowest weight. The results showed that the length of the shoe sole and the thickness of the sock are the most effective parameters in foot protection against frostbite. Using thicker socks, which only increased the weight by roughly 11%, enhanced the minimum foot temperature by more than 2.3 times. HIGHLIGHTSOptimal design of shoe geometry is used to prevent frostbite in cold environments.A model of a biothermal nonlinear model is developed for the barefoot.Length of the shoe sole and the thickness of the sock are the most effective parameters in protecting the foot against frostbite.For the selected weather conditions, the toes are most likely to have frostbite.The best shoe for the selected weather conditions is the shoe that has the highest amount of thermal insulation in the toe area.

Treatment Modelling of a 3D Tumour in Brain by Laser-Induced Interstitial Thermotherapy.

Introduction: There are some ways to examine heat transfer in tumor tissue, which is an important issue in bioengineering. One of these ways uses the bioheat equation, proposed by Pennes, in a continuous medium. Another one uses a porous medium to model heat transfer in living tissues. The objective of this paper was to study an approach to modelling the temperature distribution and tumour ablation in brain tissue and compare results to Pennes' approach. Methods: This approach presents and uses a porous medium as the tissue instead of a continuous medium. In addition, the two approaches (simulation in continuous and porous medium) are compared in terms of temperature simulation and amount of cell ablation. The density, heat conduction factor, and blood perfusion rate are considered functions of temperature. Results: In these approaches, after an 85-second treatment, the temperature increases to about 90°C. The temperature increase of the porous medium is relatively the same as that of the continuous medium and for this reason, the amount of cancerous cells that are ablated in a porous medium is approximately the same as that in a continuous medium. The volume of cell ablation is about 6500 mm3 for two ideas. In addition, the degree of damage, computed from the Arrhenius integral method, and the ablated volume of the tumour endorse equality at the end of treatment. According to the results, similar to the continuous approach, the porous approach predicts the temperature and amount of volume of damaged cells. Conclusion: Therefore, it is possible to use the porous approach instead of the Pennes approach for tumour treatment.

Optimum design of the geometry of boots and socks with the aim of minimum weight and preventing frostbite.

In order to design shoes suitable for cold environments, knowledge of the thermal conditions inside the shoes and the variables affecting those conditions is necessary. A two-dimensional model of a boot and sock was developed to investigate the effect of the materials and dimensions of various parts of shoes and to design geometry for them to prevent foot frostbite. The optimization algorithm was used to optimize the dimensions of the boots to maximize the minimum foot temperature with the lowest boot weight. Two types of shoe soles and two kinds of shoe uppers were used to design suitable shoes. The results show the following: (1) In the design boots, the thermal insulation of the toe area plays an essential role in preventing frostbite. Two variables of the thickness of the toe cap and the length of the shoe sole had the greatest impact on the design of shoes with the least weight and the most protection against frostbite. So that to increase minimum foot temperature from 7°C to 15°C, 16°C, or 17°C, only the amounts of these variables should increase. (2) In designing the suitable boot, choosing the proper shoe sole had a significant effect on increasing the thermal insulation in the shoe and reducing its weight. So, for the boot with a minimum foot temperature of 20°C, by changing the shoe sole from EVA08 to EVA12, the weight is reduced by 42%. (3) To maximize the minimum foot temperature, it is necessary to use thick socks.

Numerical study of the solidification process in biological tissue with blood flow and metabolism effects by the dual phase lag model.

The bioheat transfer with phase change in biological tissues during the freezing process is simulated by the dual phase lag conduction heat transfer model. A numerical algorithm based on the enthalpy method is established to solve the solidification of biological tissues. The linearly temperature-dependent enthalpy (non-isothermal phase change) is considered here. The results of the parabolic heat conduction model for a slice of cucumber are compared with the experimental data. A comparison between dual phase lag and hyperbolic solutions with small values of relaxation times is applied in order to verify the corresponding parabolic solutions accuracy of the dual phase lag and hyperbolic solutions. The heating source effect owing to blood perfusion and metabolic heat on the heat transfer in a biological tissue subject to freezing process is studied. The relaxation time has an important influence on the transient temperature and temperature gradient. A major discrepancy among bioheat transfer models is found for zones closer to the cooling boundary. The heat source term, owing to blood flow and metabolism in a phase change problem in the biological tissue, has a significant influence on thermal effects of the subject tissue.

New approach of controlling the area affected in brain tumour treatment by LITT.

There are some techniques to ablate tumours of brain, breast and liver. One of them is laser irradiation. The most important problem of this technique is to injure noncancerous tissues. It is a challenging work to control the domain of laser effects. In other words, it is hard to ablate cancerous tissue without ablating noncancerous. To gain this goal, some researchers have been proposed some ways, such as using two or three applicators or moving applicator. The objective of this paper is to present an approach to control the temperature distribution and heat affected zone in brain tumours when irradiated by shielded laser beam, 1064 nm ND-YAG. The effects of laser beam, resulting in tissue temperature increasing, follows the border of tumour by defining of a dual intensity distribution. This is included two distinct intensity distributions of laser on the applicator by shielding. Treatment of an arbitrary topology of tumour will be simulated irradiation of laser by two different distributions through numerical method. Results show when dual distribution on the tumour border is used, the pattern of photon distribution is coincident by the tumour and the affected zone and temperature increasing follows the borderline of tumour, qualitatively. It shows that the ablated volume of tumour will be 53% more than when the unique distribution is used and the treatment time is shorter, resultantly.