Tissue Characterisation using an Impedance Spectroscopy Probe (original) (raw)
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A new six-electrode electrical impedance technique for probing deep organs in the human body
European Biophysics Journal, 2019
Electrical impedance measurements of biological tissue have many potential applications and tetrapolar impedance measurement (TPIM) with four electrodes is traditionally used which eliminates high skin contact impedance. A linear array of four electrodes for TPIM on the horizontal plane of a cylindrical volume conductor of diameter D, where the length of the array is πD/2 with potential electrodes near the centre of the array, will give a high sensitivity near the surface which reduces rapidly with depth. A recently proposed six-electrode variation of TPIM uses an additional pair of potential electrodes on the opposite side of the volume conductor in the same horizontal plane around the circumference, with the expectation that the sensitivity of the deeper regions will thereby be enhanced. The present work carries out a finite element simulation (using COMSOL) and an experimental phantom study (saline phantom) to quantitatively evaluate the improvement obtained by this new method. The new configuration doubled the sensitivity at the central region, which was reasonably uniform over a wider zone, gradually increasing towards the potential electrodes on both sides. This would be useful for a range of biological studies of deep body organs such as lungs, stomach, and bladder. where the respective external body shapes may be approximated by an oval cylinder and where electrical impedance techniques have shown promise.
Simple electrode configurations for probing deep organs using Electrical Bio-Impedance techniques
Bangladesh Journal of Medical Physics
Tetrapolar Impedance Method (TPIM) and Focused Impedance Method (FIM) are two simple modalities of electrical bio-impedance measurement that could be employed to give useful physiological and diagnostic information of the human body. FIM is based on TPIM but uses a combination of two sets of TPIM, producing a focusing effect, which is useful to localize specific target organs. Most non-invasive electrical bio-impedance measurements based on TPIM and FIM use electrodes on one side of the body, outside the skin surface, which gives a shallow depth sensitivity. The sensitivity decreases with depth so that deep organs like lungs, heart, liver, stomach and bladder are not fully assessed through such measurements. Based on a long experience of studying electrical impedance methods, several qualitative ideas are presented in this article for probing deep organs using a few modified TPIM and FIM configurations. The suggestions are based on visualisations of both equipotentials and a popular...
Physiological Measurement, 2003
Tetrapolar probes have been widely used for measuring the impedance spectra of tissues. However, the non-uniform sensitivity distribution of these probes limits the ability to identify conductivity changes in tissue. This paper presents a novel method for improving the sensitivity distribution beneath a tetrapolar probe. The method consists of placing a hydrogel layer between the probe and the tissue in order to make the sensitivity positive everywhere within the tissue. Theoretical and measured sensitivity distributions are compared. A good agreement between theoretical and measured data from an electrolytic tank was obtained with a maximum error of 1.3%. In vivo forearm measurements showed that the use of a conductive layer does enable tissue conductivity spectra to be determined. A smaller variation between subjects was obtained when using the stand-off. It was not possible to assess the absolute accuracy of the method due to the absence of a 'gold standard' for the measurement of tissue conductivity spectra.
A Probe for Organ Impedance Measurement
IEEE Transactions on Biomedical Engineering, 2004
In this paper, we describe the theory and practical implementation of an electrical impedance probe for making in vivo measurements of the electrical admittance of living tissue. The probe uses concentric annular electrodes and is shown to sample a more localized, yet greater, volume of tissue than the standard four-electrode probe. We have developed a mathematical model for the conduction of current between the probe electrodes assuming that we are investigating a uniform, isotropic, semi-infinite region and taking into account the contact impedance between the electrodes and the organ. The electric fields produced by the probe have been calculated by solving a weakly singular Fredholm integral equation of the second kind. The size and position of the probe electrodes have been optimized to maximize both the accuracy in the admittance measurement and insensitivity to contact impedance. A probe and driving hardware have been constructed and experimental results are provided showing the accuracy of admittance measurements at 50 and 640 KHz.
Monitoring living tissues by electrical impedance spectroscopy
Annals of Biomedical Engineering, 1994
Solving the experimental difficulties associated with measurement of the electrical impedance of living tissues gives access to valuable tissue compartment parameters which are sensed within seconds using minimally invasive, simple metallic electrodes. Extracellular conductivity and cell membrane capacitance can be followed over time under conditions of metabolic toxicity, perfusion loss and thermal stress in liver, brain cortex, and muscle, respectively. Application of this technique in burns therapy allows an accurate estimation of the severity of thermal injury to skeletal muscle, supporting predictions on tissue survival.
Electrical impedance spectroscopy study of biological tissues
Journal of Electrostatics, 2008
The objective of this study was to investigate the electrical impedance properties of rat lung and other tissues ex vivo using electrical impedance spectroscopy. Rat lungs (both electroporated and naı¨ve (untreated)), and mesenteric vessels (naı¨ve) were harvested from male Sprague-Dawley rats; their electrical impedance were measured using a Solartron 1290 impedance analyzer. Mouse lung and heart samples (naı¨ve) were also studied. The resistance (real Z, O) and the reactance (Im Z, negative O) magnitudes and hence the Cole-Cole (real Z versus Im Z) plots are different for the electroporated lung and the naive lung. The results confirm the close relationship between the structure and the functional characteristic. These also vary for the different biological tissues studied. The impedance values were higher at low frequencies compared with those at high frequencies. This study is of practical interest for biological applications of electrical pulses, such as electroporation, whose efficacy depends on cell type and its electrical impedance characteristics. r
Effect of electrode geometry on the impedance evaluation of tissue and cell culture
Sensors and Actuators B-chemical, 2007
This paper explores the effect of electrode geometry on bio-impedance measurements of a simple binary electrolyte (KCl), conductive gel used in electrocardiography (ECG), human umbilical vein endothelial cell (HUVEC) culture and excised human skin tissue. The aim of this paper is (a) to understand the effect of electrode area on the impedance characteristics of various biologically relevant materials and (b) to determine the optimum microelectrode geometry for effective characterization of the electrical properties of these materials, namely, complex conductivity and permittivity. Impedance measurements were performed on four different electrode geometries in the frequency range of 100 Hz to 100 MHz. Four different materials listed above were evaluated on identical sets of electrodes. Results indicate a material-dependent lower limit of 100–50 μm electrode diameter beyond which non-uniform current distribution effects are noticeable. The skin tissue does not lend itself well to characterization using microelectrodes less than 250 μm, due to its high degree of heterogeneity.
Advances in electrical impedance methods in medical diagnostics
The electrical impedance diagnostic methods and instrumentation developed at the Gda ´ nsk and Warsaw Universities of Technology are described. On the basis of knowledge of their features, several original approaches to the broad field of electrical impedance applications are discussed. Analysis of electrical field distribution after external excitation, including electrode impedance, is of primary importance for measurement accuracy and determining the properties of the structures tested. Firstly, the problem of electrical tissue properties is discussed. Particular cells are specified for in vitro and in vivo measurements and for impedance spectrometry. Of especial importance are the findings concerning the electrical properties of breast cancer, muscle anisotropy and the properties of heart tissue and flowing blood. The applications are both important and wide-ranging but, for the present, special attention has been focused on the evaluation of cardiosurgical interventions. Second...