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Electric properties of tissues
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The electrical properties of biological tissues and cell pensions have been of interest for over a century for manyreasons, such as the ability to determine the pathways of current flow through the body and, thus, are very important in theanalysis of a wide range of biomedical applications such as functional electrical stimulation and the diagnosis and treatment of various physiological conditions with weakelectric currents, radiofrequency hyperthermia, electro-cardiography, and body composition as mentioned in this paper.Abstract:
1. INTRODUCTIONThe electrical properties of biological tissues and cell sus-pensions have been of interest for over a century for manyreasons. They determine the pathways of current flowthrough the body and, thus, are very important in theanalysis of a wide range of biomedical applications such asfunctional electrical stimulation and the diagnosis andtreatment of various physiological conditions with weakelectric currents, radio-frequency hyperthermia, electro-cardiography, and body composition. On a more funda-mental level, knowledge of these electrical properties canlead to an understanding of the underlying basic biologicalprocesses. Indeed, biological impedance studies have longbeen important in electrophysiology and biophysics; one ofthe first demonstrations of the existence of the cell mem-brane was based on dielectric studies on cell suspensions(1).To analyze the response of a tissue to electric stimula-tion, we need data on the specific conductivities and rel-ative permittivities of the tissues or organs. A microscopicdescription of the response is complicated by the variety ofcell shapes and their distribution inside the tissue as wellas the different properties of the extracellular media.Therefore, a macroscopic approach is most often used tocharacterize field distributions in biological systems.Moreover, even on a macroscopic level, the electrical prop-erties are complicated. They can depend on the tissue ori-entation relative to the applied field (directionalanisotropy), the frequency of the applied field (the tissueis neither a perfect dielectric nor a perfect conductor), orthey can be time- and space-dependent (e.g., changes intissue conductivity during electropermeabilization).2. BIOLOGICAL MATERIALS IN AN ELECTRIC FIELDThe electrical properties of any material, including bio-logical tissue, can be broadly separated into two catego-ries: conducting and insulating. In a conductor, theelectric charges move freely in response to the applicationof an electric field, whereas in an insulator (dielectric), thecharges are fixed and not free to move. A more detaileddiscussion of the fundamental processes underlying theelectrical properties of tissue can be found in Foster andSchwan (2).If a conductor is placed in an electric field, charges willmove within the conductor until the interior field is zero.In the case of an insulator, no free charges exist, so netmigration of charge does not occur. In polar materials,however, the positive and negative charge centers in themolecules do not coincide. An electric dipole moment, p,issaid to exist. An applied field, Eread more
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References
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Journal ArticleDOI
The dielectric properties of biological tissues: II. Measurements in the frequency range 10 Hz to 20 GHz
TL;DR: Three experimental techniques based on automatic swept-frequency network and impedance analysers were used to measure the dielectric properties of tissue in the frequency range 10 Hz to 20 GHz, demonstrating that good agreement was achieved between measurements using the three pieces of equipment.
Journal ArticleDOI
The dielectric properties of biological tissues: III. Parametric models for the dielectric spectrum of tissues
TL;DR: A parametric model was developed to enable the prediction of dielectric data that are in line with those contained in the vast body of literature on the subject.
Journal ArticleDOI
The dielectric properties of biological tissues: I. Literature survey
TL;DR: The dielectric properties of tissues have been extracted from the literature of the past five decades and presented in a graphical format to assess the current state of knowledge, expose the gaps there are and provide a basis for the evaluation and analysis of corresponding data from an on-going measurement programme.
Journal ArticleDOI
The specific resistance of biological material—A compendium of data for the biomedical engineer and physiologist
L. A. Geddes,L. E. Baker +1 more
TL;DR: The paper traces the history of, and tabulates determinations of the electrical resistivity of blood, other body fluids, cardiac muscle, skeletal muscle, lung, kidney, liver, spleen, pancreas, nervous tissue, fat, bone, and other miscellaneous tissues.
Journal Article
Dielectric properties of tissues and biological materials: a critical review.
Foster Kr,H. P. Schwan +1 more
TL;DR: The classical principles behind dielectric relaxation are summarized, as empirical correlations with tissue water content in other compositional variables, and a comprehensive table is presented of dielectrics properties.