Heating of tissues by microwaves: A model analysis

Foster, Kenneth R.; Lozano‐Nieto, Albert; Riu, Pere J.; Ely, Thomas S.

doi:10.1002/(sici)1521-186x(1998)19:7<420::aid-bem3>3.0.co;2-3

Cited by 64 publications

(40 citation statements)

References 12 publications

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“…As shown by model analysis, the thermal response is governed by two time constants: one pertains to heat convection by blood flow, and is of the order of 20-30 min for physiologically normal perfusion rates; the second characterizes heat conduction and varies as the square of a distance that characterizes the spatial extent of the heating (Foster et al, 1998). Experimental investigations of the temperature distribution in human brain and other tissues confirm, that the thermal time constant is large, about hundred seconds (Chua et al, 1999;Yablonskiy et al, 2000;Liu et al, 2002).…”

Section: Design Of Experimentsmentioning

confidence: 99%

Non-Thermal Effect of Microwave Radiation on Human Brain

et al. 2005

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This study focuses on an origin of interaction mechanism of microwave radiation with nervous system-quasi-thermal field effect. The microwave field can cause fluctuations and vibration of the charged particles and membranes in tissues. The hypothesis is, that this phenomenon is similar to the effect caused by Brown motion initiated by temperature and results in the same effects without rise in temperature. The electric field of 1 V/cm can introduce disturbance of the thermal equilibrium inside a cell of 10 µm radius, which is equivalent to disturbance produced by temperature rise of 1 K. The hypothesis, that microwave heating should cause an effect independent of the microwave modulation frequency, while field effect depends on modulation frequency, was examined experimentally. The 450 MHz microwave radiation, modulated at 7, 14 and 21 Hz frequencies, power density at the skin 0.16 mW/cm 2 , was applied. The experimental protocol consisted of two series of five cycles of the repetitive microwave exposure at fixed modulation frequencies. Relative changes in EEG theta, alpha and beta rhythms of the group of 13 healthy volunteers were analysed. Analysis of the experimental data shows that:(1) statistically significant changes in EEG rhythms depend on modulation frequency of the microwave field; (2) microwave stimulation causes an increase of the EEG energy level; (3) the effect is most intense at beta1 rhythm and higher modulation frequencies. These findings confirm the quasi-thermal origin of the effect, different from average heating.

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Section: Design Of Experimentsmentioning

confidence: 99%

Non-Thermal Effect of Microwave Radiation on Human Brain

et al. 2005

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“…This is, however, not the case with cell suspensions or tissues, where heat¯ow is always present and results in heat redistribution. Therefore, while Equation 3 correctly describes the power dissipation, the resulting temperature increase in each particular region is much less straightforward to determine and can be approximated as proportional to the power dissipation only for very short exposures, where heat transfer is negligible [Foster et al, 1998]. Thus, in this paper we focus exclusively on the power dissipation predicted by various physical models.…”

Section: Introduction Power Dissipation and Temperature Increase Causmentioning

confidence: 99%

Theoretical evaluation of the distributed power dissipation in biological cells exposed to electric fields

Kotnik

Miklav?i?

2000

Bioelectromagnetics

149

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The paper deals with the power dissipation caused by exposure of biological cells to electric fields of various frequencies. With DC and sub-MHz AC frequencies, power dissipation in the cell membrane is of the same order of magnitude as in the external medium. At MHz and GHz frequencies, dielectric relaxation leads to dielectric power dissipation gradually increasing with frequency, and total power dissipation within the membrane rises significantly. Since such local increase can lead to considerable biochemical and biophysical changes within the membrane, especially at higher frequencies, the bulk treatment does not provide a complete picture of effects of an exposure. In this paper, we theoretically analyze the distribution of power dissipation as a function of field frequency. We first discuss conductive power dissipation generated by DC exposures. Then, we focus on AC fields; starting with the established first-order model, which includes only conductive power dissipation and is valid at sub-MHz frequencies, we enhance it in two steps. We first introduce the capacitive properties of the cytoplasm and the external medium to obtain a second-order model, which still includes only conductive power dissipation. Then we enhance this model further by accounting for dielectric relaxation effects, thereby introducing dielectric power dissipation. The calculations show that due to the latter component, in the MHz range the power dissipation within the membrane significantly exceeds the value in the external medium, while in the lower GHz range this effect is even more pronounced. This implies that even in exposures that do not cause a significant temperature rise at the macroscopic, whole-system level, the locally increased power dissipation in cell membranes could lead to various effects at the microscopic, single-cell level.

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“…(1) with a temperature-independent blood perfusion rate w will be studied, which is a good approximation when heat mainly propagates in the direction perpendicular to the skin surface. Studies that predict temperature distribution in living tissues usually assume a constant thermal conductivity of tissue within the tissue [23], [24], [25], [26], [27], [28]. However, some experimental studies showed that the blood flow via blood vessels has significant influence on the thermal conductivity of living biological tissue [29], [30], [31], [32].…”

Section: Introductionmentioning

confidence: 99%

Bioheat transfer problems with spatial or transient heating on skin surface or inside biological bodies

Kengne

Mellal

Lakhssassi

2014

2014 7th International Conference on Biomedical Engineering and Informatics

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A bioheat transfer model with quadratic temperature-dependent thermal conductivity is considered in this work. Applying the Taylor expansion method, we have investigated the bioheat transfer problems with generalized spatial or transient heating both on skin surface and inside the biological bodies. The effect of the temperature-dependent thermal conductivity on the nonlinear temperature distribution is studied. The method used in this paper can be useful to investigate several typical bioheat transfer processes, which are often encountered in cancer hyperthermia, laser surgery, thermal comfort analysis, and tissue thermal parameter estimation.

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Heating of tissues by microwaves: A model analysis

Cited by 64 publications

References 12 publications

Non-Thermal Effect of Microwave Radiation on Human Brain

Non-Thermal Effect of Microwave Radiation on Human Brain

Theoretical evaluation of the distributed power dissipation in biological cells exposed to electric fields

Bioheat transfer problems with spatial or transient heating on skin surface or inside biological bodies

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