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Journal ArticleDOI

A New Simplified Bioheat Equation for the Effect of Blood Flow on Local Average Tissue Temperature

01 May 1985-Journal of Biomechanical Engineering-transactions of The Asme (American Society of Mechanical Engineers)-Vol. 107, Iss: 2, pp 131-139
TL;DR: A new simplified three-dimensional bioheat equation is derived to describe the effect of blood flow on blood-tissue heat transfer and shows that the vascularization of tissue causes it to behave as an anisotropic heat transfer medium.
Abstract: A new simplified three-dimensional bioheat equation is derived to describe the effect of blood flow on blood-tissue heat transfer. In two recent theoretical and experimental studies [1, 2] the authors have demonstrated that the so-called isotropic blood perfusion term in the existing bioheat equation is negligible because of the microvascular organization, and that the primary mechanism for blood-tissue energy exchange is incomplete countercurrent exchange in the thermally significant microvessels. The new theory to describe this basic mechanism shows that the vascularization of tissue causes it to behave as an anisotropic heat transfer medium. A remarkably simple expression is derived for the tensor conductivity of the tissue as a function of the local vascular geometry and flow velocity in the thermally significant countercurrent vessels. It is also shown that directed as opposed to isotropic blood perfusion between the countercurrent vessels can have a significant influence on heat transfer in regions where the countercurrent vessels are under 70-micron diameter. The new bioheat equation also describes this mechanism.
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Journal ArticleDOI
TL;DR: The main concepts studied in this review are transport in porous media using mass diffusion and different convective flow models such as Darcy and the Brinkman models as mentioned in this paper, and energy transport in tissues is also analyzed.

637 citations


Cites background or methods from "A New Simplified Bioheat Equation f..."

  • ...This causes the tissue–blood medium to be anisotropic with respect to the thermal conductivity in addition to the corresponding anisotropy indicated by Weinbaum and Jiji [42] due to concurrent blood flows....

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  • ...An important research work example that utilized Weinbaum and Jiji s [42] model is the work of Guiot et al. [43]....

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  • ...They used the Weinbaum and Jiji s model, assuming a linear relation between the effective thermal conductivity and the blood perfusion rate, to determine the increase in the thermal conductivity in a perfused tissue....

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  • ...Accordingly, Weinbaum and Jiji [42] modified the thermal conductivity in the Pennes equation by means of an ‘‘effective conductivity’’ related quadratically to blood perfusion rate which is affected by the dimensions and the directions of the vessels....

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  • ...This density distribution is unstable, and convective motions are Table 3 Summary of presented bioheat transfer models Bioheat transfer model Main features Pennes [38] • simple • based on uniform perfusion • it is not valid for all tissues Weinbaum and Jiji [41] • valid when arteries and veins are close leading to negligible blood perfusion effects • utilizes an effective conductivity as function of the perfusion rate Wissler [44] • avoids assumptions of the Weinbaum and Jiji s [41] model Baish [45] • complex and statistical based model • considers simulation of a realistic vascular tree containing all thermally significant vessels Weinbaum et al. [46] • includes an efficiency term in Pennes source term to make Pennes equation applicable to muscle tissues Theory of porous media (Principle of local thermal equilibrium) Amiri and Vafai [50,51], Khanafer and Vafai [52], Marafie and Vafai [53], Alazmi and Vafai [37], Xuan and Roetzel [48,49] • modifies Pennes equation by considering the following effects (a) variations in the tissue porosity (b) blood dispersion (c) considers effective tissue conductivity (d) considers effective tissue capacitance Theory of porous media (Principle of local thermal non-equilibrium) Amiri and Vafai [50,51], Alazmi and Vafai [52], Khanafer and Vafai [54], Marafie and Vafai [55], Kuznetsov and Vafai [56], Xuan and Roetzel [48,49] • exact blood perfusion is included • complex and require more flow and thermal information • considers (a) variations in the tissue porosity (b) blood dispersion (c) considers effective tissue conductivity (d) considers effective tissue capacitance set up as in a shallow fluid heated from below....

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Journal ArticleDOI
TL;DR: A broad overview of magnetic hyperthermia addressing new perspectives and the progress on relevant features such as the ad hoc preparation of magnetic nanoparticles, physical modeling of magnetic heating, methods to determine the heat dissipation power of magnetic colloids including the development of experimental apparatus and the influence of biological matrices on the heating efficiency is presented in this article.
Abstract: Nowadays, magnetic hyperthermia constitutes a complementary approach to cancer treatment. The use of magnetic particles as heating mediators, proposed in the 1950s, provides a novel strategy for improving tumor treatment and, consequently, patient's quality of life. This review reports a broad overview about several aspects of magnetic hyperthermia addressing new perspectives and the progress on relevant features such as the ad hoc preparation of magnetic nanoparticles, physical modeling of magnetic heating, methods to determine the heat dissipation power of magnetic colloids including the development of experimental apparatus and the influence of biological matrices on the heating efficiency.

545 citations

Journal ArticleDOI
TL;DR: Constructal theory is the view that the generation of flow configuration is a physics phenomenon that can be based on a physics principle (the constructal law): "For a finite-size flow system to persist in time (to survive) its configuration must evolve in such a way that it provides an easier access to the currents that flow through it".
Abstract: Constructal theory is the view that the generation of flow configuration is a physics phenomenon that can be based on a physics principle (the constructal law): “For a finite-size flow system to persist in time (to survive) its configuration must evolve in such a way that it provides an easier access to the currents that flow through it” [A. Bejan, Advanced Engineering Thermodynamics, 2nd ed. (Wiley, New York, 1997); Int. J. Heat Mass Transfer, 40, 799 (1997)]. This principle predicts natural configuration across the board: river basins, turbulence, animal design (allometry, vascularization, locomotion), cracks in solids, dendritic solidification, Earth climate, droplet impact configuration, etc. The same principle yields new designs for electronics, fuel cells, and tree networks for transport of people, goods, and information. This review describes a paradigm that is universally applicable in natural sciences, engineering and social sciences.

445 citations

Journal ArticleDOI
TL;DR: The present review compares and contrasts several of the new bio-heat transfer models, emphasizing the problematics of their experimental validation, in the absence of measuring equipment capable of reliable evaluation of tissue properties and their variations that occur in the spatial scale of blood vessels with diameters less than about 0.2 mm.
Abstract: Successful hyperthermia treatment of tumors requires understanding the attendant thermal processes in both diseased and healthy tissue. Accordingly, it is essential for developers and users of hyperthermia equipment to predict, measure and interpret correctly the tissue thermal and vascular response to heating. Modeling of heat transfer in living tissues is a means towards this end. Due to the complex morphology of living tissues, such modeling is a difficult task and some simplifying assumptions are needed. Some investigators have recently argued that Pennes' interpretation of the vascular contribution to heat transfer in perfused tissues fails to account for the actual thermal equilibration process between the flowing blood and the surrounding tissue and proposed new models, presumably based on a more realistic anatomy of the perfused tissue. The present review compares and contrasts several of the new bio-heat transfer models, emphasizing the problematics of their experimental validation, in the absence of measuring equipment capable of reliable evaluation of tissue properties and their variations that occur in the spatial scale of blood vessels with diameters less than about 0.2 mm. For the most part, the new models still lack sound experimental grounding, and in view of their inherent complexity, the best practical approach for modeling bio-heat transfer during hyperthermia may still be the Pennes model, providing its use is based on some insights gained from the studies described here. In such cases, these models should yield a more realistic description of tissue locations and/or thermal conditions for which the Pennes model might not apply. >

420 citations

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TL;DR: An overview of wearables market trends, different active and passive methods of body energy harvesting for powering low-consumption electronic devices are introduced, and challenges of device fabrication are discussed.

323 citations