Temperature Distribution In Biological Tissue Research Articles

Modified Pennes bioheat equation with heterogeneous blood perfusion: A newer perspective

The Pennes bioheat equation is a widely used mathematical model for predicting temperature distribution in biological tissues. However, it assumes homogeneous blood perfusion throughout the tissue, which may not accurately represent the complex perfusion patterns observed in tumors. In this study, we propose modification to traditional Pennes bioheat equation that incorporates the effects of perfusion heterogeneity by introducing a spatially varying perfusion term, represented by a perfusion coefficient, ωb(x,y,z) to account for local variations in blood flow at each spatial location within the biological tissue. Therefore, heterogeneous blood perfusion at each tumor tissue voxel location relax the uniform blood perfusion assumption. By incorporating these modifications, the model allows for a more realistic representation of the heat exchange between the biological tissue and blood flow, by predicting the non-uniform temperature distribution particularly in tumors with irregular blood vessel growth and organization, thereby facilitating treatment planning and optimization of thermal therapies, and leading to more effective therapeutic outcomes. The spatially varying perfusion coefficient can be obtained through advanced imaging techniques such as dynamic contrast-enhanced MRI or Doppler ultrasound enabling the assessment of perfusion heterogeneity in biological tissues. In conclusion, the modified Pennes bioheat equation offers a valuable tool for understanding the intricate relationship between with heterogeneous blood perfusion and temperature distribution in biological tissues, providing important insights to the thermal response of tumors and guiding the development of improved therapeutic strategies in optimizing cancer treatments.

Theoretical Evaluation of Microwave Ablation Applied on Muscle, Fat and Bone: A Numerical Study

(1) Background: Microwave ablation (MWA) is a common tumor ablation surgery. Because of the high temperature of the ablation antenna, it is strongly destructive to surrounding vital tissues, resulting in high professional requirements for clinicians. The method used to carry out temperature observation and damage prediction in MWA is significant; (2) Methods: This work employs numerical study to explore temperature distribution of typical tissues in MWA. Firstly, clinical MWA based on isolated biological tissue is implemented. Then, the Pennes models and microwave radiation physics are established based on experimental parameters and existing related research. Initial values and boundary conditions are adjusted to better meet the real clinical materials and experimental conditions. Finally, clinical MWA data test this model. On the premise that the model is matched with clinical MWA, fat and bone are deduced for further heat transfer analysis. (3) Results: Numerical study obtains the temperature distribution of biological tissue in MWA. It observes the heat transfer law of ablation antenna in biological tissue. Additionally, combined with temperature threshold, it generates thermal damage of biological tissues and predicts the possible risks in MWA; (4) Conclusions: This work proposes a numerical study of typical biological tissues. It provides a new theoretical basis for clinically thermal ablation surgery.

Investigation of initial value dependence in the statistical analysis of ultrasonic scattered echoes for the non-invasive estimation of temperature distribution in biological tissue

In the present study, the variation of the Nakagami shape parameter m of the probability distribution of amplitudes of ultrasonic echoes from soft tissue due to a temperature increase is shown to exhibit initial m-value dependence. The change of the Nakagami shape parameter m due to the temperature rise increased with increasing the initial m-value. In order to measure the temperature distribution in soft tissue, we propose a parameter that indicates the absolute values of ratio changes of m values with the multiplying factor varying as a function of the initial m-value. In the hot-scale images indicating the absolute values of ratio changes of m values with the consideration of the initial m-value dependence, the temperature distribution in soft tissue was visualized clearly.

Numerical simulation of temperature variations in a canine knee joint during therapeutic heating

Tissue heating is used for the treatment of health disorders. However, the benefits of this therapy depend heavily on the temperature reached in the tissues. Values outside the ideal range recommended for therapeutic effects may result in ineffective or tissue-damaging treatments. Thus, understanding the heat transfer process and knowing the temperature distribution in biological tissues are essential factors for this treatment to be applied safely and effectively. In this context, the numerical simulation becomes an interesting tool to understand the temperature field in the different tissues that make up the joint and, thus, to contribute to a better application of the thermal resources used in the clinical practice of physiotherapy. This study aimed to simulate the transient heat transfer in a canine knee joint during the application of a therapeutic heating feature and to investigate the effects of blood perfusion performed at a constant rate (A1 simulation) and as a function of tissue temperature distribution (A2 simulation). The heat diffusion equation was used to model the heat transfer phenomenon. The simulations were performed using the ANSYS-CFX® program. The results obtained from the simulations were compared with in vivo experimental data. The A1 simulation showed a maximum percentage difference of 25.6% compared to the experimental data. In contrast, the highest percentage difference found for the A2 simulation was 9.8%. In conclusion, the results suggest that simulation can be an important tool to evaluate the temperature behaviour of biological tissues during the application of thermal therapeutic resources.

Identification of Laser Intensity Assuring the Destruction of Target Region of Biological Tissue Using the Gradient Method and Generalized Dual-Phase Lag Equation

Temperature distribution in biological tissue is described by dual-phase lag model supplemented by appropriate boundary and initial conditions. Laser–tissue interactions are taken into account in the source function occurring in this model. The problem is solved using the finite difference method. Next, the Arrhenius integral which is a measure of tissue destruction is calculated. The inverse problem formulated here is to estimate the laser intensity assuring the destruction of this tissue region for which the Arrhenius integral exceeds the critical value.

2P5-13 Ultrasonic measurement of temperature distribution of biological tissue by local heating(Poster Session)

2P5-13 Ultrasonic measurement of temperature distribution of biological tissue by local heating(Poster Session)

Effect of convective term on temperature distribution in biological tissue

We introduce a phase imprint into the order parameter describing the influence of blood flow on the temperature distribution in the tissue described by the one-dimensional Pennes equation and then engineer the imprinted phase suitably to generate a modified Pennes equation with a gradient term (known in the theory of biological systems as convective term) which is associated with the heat convected by the flowing blood. Using the derived model, we analytically investigate temperature distribution in biological tissues subject to two different spatial heating methods. The applicability of our results is illustrated by one of typical bio-heat transfer problems which is often encountered in therapeutic treatment, cancer hyperthermia, laser surgery, thermal injury evaluation, etc. Analyzing the effect of the convective term on temperature distribution, we found that an optimum heating of a biological system can be obtained through regulating the convective term.

Investigation of nonlinear temperature distribution in biological tissues by using bioheat transfer equation of Pennes’ type

In this paper, a two level finite difference scheme of Crank-Nicholson type is constructed and used to numerically investigate nonlinear temperature distribution in biological tissues described by bioheat transfer equation of Pennes’ type. For the equation under consideration, the thermal conductivity is either depth-dependent or tem-perature-dependent, while blood perfusion is temperature-dependent. In both cases of depth- dependent and temperature-dependent thermal conductivity, it is shown that blood perfusion decreases the temperature of the living tissue. Our numerical simulations show that neither the localization nor the magnitude of peak tempera-ture is affected by surface temperature; however, the width of peak temperature increases with surface temperature.

Dimensionless solutions and general characteristics of bioheat transfer during thermal therapy

The derivation and application of the general characteristics of bioheat transfer for medical applications are shown in this paper. Two general bioheat transfer characteristics are derived from solutions of one-dimensional Pennes’ bioheat transfer equation: steady-state thermal penetration depth, which is the deepest depth where the heat effect reaches; and time to reach steady-state, which represents the amount of time necessary for temperature distribution to converge to a steady-state. All results are described by dimensionless form; therefore, these results provide information on temperature distribution in biological tissue for various thermal therapies by transforming to dimension form.

Simulation of heat transfer of biological tissue during cryosurgery based on vascular trees

During the freezing process in cryosurgery, the blood flow and blood perfusion have great influence on the heat transfer of the biological tissue. The effect of blood vessels on the temperature distribution of biological tissue is studied in this paper. The blood vessels are assumed as vascular trees using fractal methods. The method is based on the calculation of the ‘fractal dimension’ of blood vessels, considering the parameters of blood vessels and blood flows. The biological tissue is assumed as porous media and a numerical model of phase change heat transfer in biological tissue is established. The temperature distribution in biological tissue considering the effect of blood flow is simulated. The effect of the geometry of the vascular tree on the phase change heat transfer in biological tissue during cryosurgery is also analyzed.

Estimation of temperature distribution in biological tissue by using solutions of bioheat transfer equation

AbstractA living body has a system for maintaining its temperature. We have investigated the heat transfer characteristics common to each organ and therapy using heat transfer. The one‐dimensional bioheat transfer equation with bioheat generation was converted into a dimensionless form and solved by Laplace transformation on the assumption that biological tissue is homogeneous. A dimensionless steady‐state solution and transient solution were derived analytically. These solutions can represent the characteristics of the temperature distribution common to each organ. Comparison with numerical solutions has confirmed that these solutions can be applied to estimate the temperature distribution of inhomogeneous biological tissue. It is proved that the size of the region where temperature change occurs, the steady‐state thermal penetration depth, is decided by biological properties. Furthermore, the time needed to reach a steady state, or the time it takes for biological tissue to reach a steady state, is calculated by using these solutions. Additionally, a temperature chart was proposed for each organ or tissue. This chart can serve as a guideline for medical doctors in formulating thermal therapy. © 2008 Wiley Periodicals, Inc. Heat Trans Asian Res, 37(6): 374– 386, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20210

Laser photothermolysis of biological tissues by using plasmon-resonance particles

The spatial temperature distribution in biological tissues upon interaction of laser radiation with plasmon-resonance nanoparticles is simulated numerically. Experimental thermograms of model objects and real biological tissues are obtained in vivo for different localisation depths of nanoparticles in different irradiation regimes. The results obtained in the study can be used for the development of methods of laser photothermolysis of malignant tumours.

Estimation of Temperature Distribution in Biological Tissue by Using Solutions of Bioheat Transfer Equation

A living body has a system to maintain its own temperature. We have investigated the heat transfer characteristic common to each organ and therapy. One-dimensional bioheat transfer equation with bioheat generation was transformed to dimensionless form and solved by Laplace transformation on the assumption that biological tissue is homogeneous. Dimensionless steady state solution and transient solution were derived analytically. These solutions can be represented temperature distribution of organ. It is confirmed that these solutions can be applied to estimate temperature distribution of inhomogeneous biological tissue by comparison with numerical solution. It is proved that the size of region where temperature change occurs, steady state thermal penetration depth, is decided by biological properties. Furthermore reaching time to steady state, or the time that biological tissue becomes steady state, is calculated by using these solutions. Additionally temperature chart was proposed for each organs or tissue. This temperature chart can be guideline for medical doctors in the thermal therapy.

Relationship between the temperature and the acoustic nonlinearity parameter in biological tissues

Recently with the rapid development of the high-intensity focused ultrasound (HIFU) in biomedical ultrasound, much attention has been paid to the noninvasive temperature estimation in biological tissue in order to determine the region and degree of the ultrasound-induced lesions. In ultrasound hyperthermal therapy it is highly desirable to study the real-time noninvasive monitoring of temperature distribution in biological tissue. In this paper, the relationship between the nonlinearity parameterB/A and the temperature in biological tissue is studied and compared with the theoretical model as well as the experimental results from the thermocouple. Results indicated thatB/A could be used as an effective tool to monitor the temperature distribution in biological media.

Temperature distribution under irradiation of pathologically changed tissue by an excimer laser

A theoretical model of the temperature distribution of biological tissue under pulsed laser illumination is developed. With the help of the elaborated miniature thermometer based on a shieldless silicon transistor, the spatial-temporal distribution of temperatures of the artery inner wall with atherosclerotic inclusions (in vitro) under excimer-laser illumination as a function of laser power and the distance between the thermometer and laser spot on the tissue surface was experimentally measured. From a comparison of experimental data with the results of the model developed, the thermal diffusivity of tissue and the size of the “region of damage” (i.e., the region where the temperature exceeds 43–45°C) under laser removal (ablation) of the tissue was determined, as well as the threshold energy density of the ablation onset.

Multiangle method for temperature measurement of biological tissues by microwave radiometry

A new approach for deriving the temperature distribution in biological tissues of microwave radiometry is proposed. It consists in the measurement of the thermal radiation of the body, at a given frequency, as a function of the observation angle, for two mutually orthogonal polarizations. Theoretically, this method yields results comparable to those obtained with the multispectral method. In order to derive the relations between the body temperature and the emitted thermal signal, the biological body is modeled by a set of parallel planar layers, each characterized by constant permittivity and temperature. It is demonstrated that for all practical purposes the radiation pattern of the antenna may be approximated by that of an unbounded plane wave.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Electromagnetic remote sensing of the temperature profile in a stratified medium of biological tissues by stochastic inversion of radiometric data

Some results are presented from investigations studying the process of inversion of multispectral microwave radiometric data to determine the subcutaneous temperature distribution in biological tissues. A transmission line concept is used to model a three‐layer planar configuration as typical for the tissue composition of a human upper arm (skin‐fat‐muscle). Computer‐simulated data are generated at 3, 5, and 10 GHz using the Rayleigh‐Jeans approximation and the radiative transfer approach. Starting from a characteristic temperature profile, the radiometric data set is inverted to yield reconstructed values of the profile. Using the process of stochastic inversion, it is shown how to compromise between penetration depths, temperature resolution, and confidence level of the temperature values retrieved.