Numerical study on the effects of blood perfusion and tumor metabolism on tumor temperature for targeted hyperthermia considering a realistic geometrical model of head layers using the finite element method

The main aim of the present work is to determine the temperature distribution in the normal and cancerous tissues to achieve the desired condition of hyperthermia. Hyperthermia can be defined as the mild elevation of the temperature to 40–46 °C, which induces the cancer cell death and enhances the effects of the radiotherapy and chemotherapy. In the present research, the realistic geometry of the human head layers and the tumor are modelled, geometrically, and then simulated similar to the real samples of MRI images with the size of 5990 mm3. The temperature distribution in the tumor and healthy tissues was obtained based on the solution of Penne’s bio-heat transfer equation utilizing the Finite Element scheme. Employing the accurate boundary conditions for the thermal simulation of the problem, two main layers of the human brain, namely, white matter (WM) and gray matter (GM), as well as the cerebrospinal fluid (CSF) and the skull, are considered in the thermal analysis. In order to examine the hyperthermia conditions, the effects of the different blood perfusion rates and tumor metabolism on the tumor temperature are analyzed. The results showed that by reducing the blood perfusion rate from 0.0016 to 0.0005(ml/(ml.s)), the temperature increased by nearly 0.2 ℃ at the center of the tumor implying that the variations of the blood perfusion rate in the tumor have not a significant influence on its temperature. Moreover, it was found that when the tumor metabolism increases five times (equal to 125 × 103 W/m3) than its normal value (equal to 25,000 W/m3), the temperature reaches to the range needed for ablation of the brain tumor (40–46 ℃). The results also indicated that the manipulation of the cancer tissues metabolic rate via thermal simulation could be efficiently employed to estimate the amount of heat needed for the thermal ablation of the tumor.

Computational Modelling of Dual-Phase Lag Bioheat Process in Cooling of Cutaneous Tissue Exposed to High Heating for Burn Injury Prediction

Heat transfer in biological systems is critical in analytic and therapeutic burn applications. Timely burn evaluation and appropriate clinical management are critical to ameliorate the treatment outcome of burn patients. To apply appropriate burn treatment, it is necessary to understand the thermal parameters of the skin. The paper aims to model the non-Fourier bioheat process in the human skin using a multi-domain trivariate spectral collocation method to determine skin burn injury with non-ideal properties of tissue, blood perfusion and metabolism. The skin tissue internal water evaporation during direct heating is considered. Parametric studies on the effects of skin tissue properties, initial temperature, blood perfusion rate and heat transfer parameters for the thermal response and exposure time of triple-layer cutaneous tissues are carried out. The study shows that the initial tissue temperature, the thermal conductivity of the epidermis and dermis, relaxation and thermalisation time and convective heat transfer coefficient are critical parameters necessary for skin burn injury baseline examination. The thermal conductivity and blood perfusion rate also exhibit negligible effects on the burn injury threshold of the cutaneous tissue. The present study is aimed to assist burn evaluation for reliable experimentation, design and optimisation of thermal therapy delivery.

METHOD OF FUNDAMENTAL SOLUTIONS FOR NONLINEAR SKIN BIOHEAT MODEL

In this paper, the method of fundamental solution (MFS) coupling with the dual reciprocity method (DRM) is developed to solve nonlinear steady state bioheat transfer problems. A two-dimensional nonlinear skin model with temperature-dependent blood perfusion rate is studied. Firstly, the original bioheat transfer governing equation with nonlinear term induced by temperature-dependent blood perfusion rate is linearized with the Taylor's expansion technique. Then, the linearized governing equation with specified boundary conditions is solved using a meshless approach, in which the DRM and the MFS are employed to obtain particular and homogeneous solutions, respectively. Several numerical examples involving linear, quadratic and exponential relations between temperature and blood perfusion rate are tested to verify the efficiency and accuracy of the proposed meshless model in solving nonlinear steady state bioheat transfer problems, and also the sensitivity of coefficients in the expression of temperature-dependent blood perfusion rate is analyzed for investigating the influence of blood perfusion rate to temperature distribution in skin tissues.

Inert gas clearance from tissue by co-currently and counter-currently arranged microvessels

To elucidate the clearance of dissolved inert gas from tissues, we have developed numerical models of gas transport in a cylindrical block of tissue supplied by one or two capillaries. With two capillaries, attention is given to the effects of co-current and counter-current flow on tissue gas clearance. Clearance by counter-current flow is compared with clearance by a single capillary or by two co-currently arranged capillaries. Effects of the blood velocity, solubility, and diffusivity of the gas in the tissue are investigated using parameters with physiological values. It is found that under the conditions investigated, almost identical clearances are achieved by a single capillary as by a co-current pair when the total flow per tissue volume in each unit is the same (i.e., flow velocity in the single capillary is twice that in each co-current vessel). For both co-current and counter-current arrangements, approximate linear relations exist between the tissue gas clearance rate and tissue blood perfusion rate. However, the counter-current arrangement of capillaries results in less-efficient clearance of the inert gas from tissues. Furthermore, this difference in efficiency increases at higher blood flow rates. At a given blood flow, the simple conduction-capacitance model, which has been used to estimate tissue blood perfusion rate from inert gas clearance, underestimates gas clearance rates predicted by the numerical models for single vessel or for two vessels with co-current flow. This difference is accounted for in discussion, which also considers the choice of parameters and possible effects of microvascular architecture on the interpretation of tissue inert gas clearance.