Impedance Of Biological Tissues Research Articles

A TECHNIQUE FOR EXPERIMENTAL DATA PROCESSING AT MODELING THE DISPERSION OF THE BIOLOGICAL TISSUE IMPEDANCE USING THE FRICKE EQUIVALENT CIRCUIT

Purpose. Modeling the dispersion of the biological tissue impedance of vegetable and animal origin using the Fricke equivalent circuit; development of a technique for experimental data processing to determine the approximation coefficients of the dispersion of the biological tissue impedance for this equivalent circuit; study of the features of the equivalent circuit at modeling the dispersion of the impedance, resistance, and reactance; the definition of the frequency domain in which using of the equivalent circuit is correct; revealing and generalization of the main regularities of dissipation of biological tissue impedance of vegetable and animal origin. Methodology. The technique is based on the scientific provisions of theoretical electrical engineering – the theory of the electromagnetic field in nonlinear media in modeling the dispersion of the biological tissue impedance. Results. The electric circuit of the Fricke equivalent circuit allows modeling the dependences of the impedance module of biological tissues, active and reactive components of impedance with acceptable accuracy for practical purposes in the frequency domain from 103 to 106 Hz. The equation of impedance of the Fricke equivalent circuit for biological tissues makes it possible to approximate the frequency dependences of the impedance modulus, active and reactive parts of the total resistance only by using the approximation coefficients corresponding to each part. The developed method for determining the values of the approximation coefficients of the impedance equation for the Fricke equivalent circuit for biological tissues allows to determine these values with high accuracy for various biological tissues. It is shown that the frequency dependences of the active component of the total resistance for tissues of vegetable and animal origin are similar. Originality. The developed technique operates with the normalized values of the impedance modulus of the Fricke equivalent circuit, the active and reactive components of the impedance as a function of frequency, which allows a comparative analysis of the dependencies of these parameters of various biological tissues of plant and animal origin. Practical value. The approximate dependences of the absolute impedance modulus, active and reactive components of the impedance allow modeling processes occurring in biological tissues with the passage of a current of different frequency. Dependence of the impedance of biological tissue can be applied to the design of diagnostic and control equipment to determine the properties of tissues of animal and vegetable origin, including developing more effective medical equipment.

Variability of Cole-model bioimpedance parameters using magnitude-only measurements of apples from a two-electrode configuration

ABSTRACTElectrical impedance measurements have been widely researched to monitor physiological changes in fruits and vegetables in a nondestructive manner. Recently, the parameters of the Cole bioimpedance model (R0, R1, C, and α), an equivalent circuit that is widely used to represent the electrical impedance of biological tissues, were extracted using techniques without direct impedance measurements. In this study, the variability of the Cole parameters extracted from magnitude-only measurements (from 200 Hz to 1 MHz) of apples in a two-electrode setup was examined to understand the impact of electrode placement on the parameters evaluated using this technique. Eight electrodes were placed around the center latitudinal line of apples to collect seven sets of measurements from four different varieties (Granny Smith, Fuji, Red Delicious, and Spartan). The Cole impedance parameters were extracted in MATLAB from the collected measurements using a nonlinear least squares fitting method. These extractions indicated that the parameters R0 and R1 had the highest variability based on the electrode location, whereas the dispersion coefficient (α) had the lowest variability.

Determining the level of resection of the intestine in experimental acute intestinal obstruction using bioimpedance

Актуальность. Определение границ необратимого повреждения кишки в условиях острой кишечной непроходимости является одной из важнейших задач, выполняемых в ходе оперативного лечения данной патологии.Цель исследования: улучшение результатов хирургического лечения острой кишечной непроходимости путем уменьшения объема резекции кишки при ее некрозе.Материалы и методы. Исследование выполнено на 64 белых крысах линии «Вистар» массой 180-230 г. Под наркозом проводили срединную лапаротомию и моделировали острую странгуляционную тонкокишечную непроходимость путем наложения толстой лигатуры на петлю тонкой кишки (длиной 1,5-2 см) вместе с брыжейкой. Моделирование патологического процесса было произведено на сроки 1 час (n=11), 3 часа (n=13) и 6 часов (n=12). На 13 животных были исследованы показатели импеданса тонкой кишки в норме. Отдельную группу (n=15) составили животные, которым произведено моделирование острой кишечной непроходимости сроком на 3 часа с последующей резекцией кишки на различных уровнях и формированием кишечных анастомозов. Инвазивную биоимпедансометрию (БИМ) кишечной стенки производили с помощью устройства для измерения импеданса биологических тканей БИМ-II (Патент РФ №2366360). В качестве калибровки прибора перед исследованием in vitro измеряли импеданс физиологического раствора. Исследуемые участи кишки подвергались гистологическому исследованию.Результаты и их обсуждение. Величина импеданса физиологического раствора составила 0,46 кОм. При изучении изменений показателей БИМ приводящего и отводящего отделов тонкой кишки выявлено, что значения уменьшаются по направлению к зоне странгуляции, наиболее низкие величины регистрировались на границе с зоной странгуляции. По данным гистологического исследования тонкой кишки в зонах, где регистрировали показатели биоимпедансометрии ниже 2 кОм в условиях острой кишечной непроходимости, выявлены признаки некроза различной выраженности. При этом максимальное значение импеданса в этих участках было равно 1,99 кОм. В зонах кишки, где регистрировали показатели импеданса выше 2 кОм, независимо от сроков патологического процесса, признаков некроза обнаружено не было. При определении границ резекции кишки ориентиром служила величина импеданса выше 2 кОм.Гистологическое исследование кишечных анастомозов, выполненных при резекции кишки в условиях острой кишечной непроходимости с учетом данных биоимпедансометрии, и анастомозов, выполненных при резекции органа в пределах заведомо жизнеспособных тканей, не выявило существенных различий в гистоморфологической картине заживления.Выводы. Значение биоимпедансометрии участков приводящего и отводящего отделов кишки выше 2 кОм является критерием при определении границ резекции органа.Ключевые слова: эксперимент, острая кишечная непроходимость, жизнеспособность кишки, биоимпедансометрия.

A LabVIEW-based electrical bioimpedance spectroscopic data interpreter (LEBISDI) for biological tissue impedance analysis and equivalent circuit modelling

Abstract Under an alternating electrical signal, biological tissues produce a complex electrical bioimpedance that is a function of tissue composition and applied signal frequencies. By studying the bioimpedance spectra of biological tissues over a wide range of frequencies, we can noninvasively probe the physiological properties of these tissues to detect possible pathological conditions. Electrical impedance spectroscopy (EIS) can provide the spectra that are needed to calculate impedance parameters within a wide range of frequencies. Before impedance parameters can be calculated and tissue information extracted, impedance spectra should be processed and analyzed by a dedicated software program. National Instruments (NI) Inc. offers LabVIEW, a fast, portable, robust, user-friendly platform for designing data-analyzing software. We developed a LabVIEW-based electrical bioimpedance spectroscopic data interpreter (LEBISDI) to analyze the electrical impedance spectra for tissue characterization in medical, biomedical and biological applications. Here, we test, calibrate and evaluate the performance of LEBISDI on the impedance data obtained from simulation studies as well as the practical EIS experimentations conducted on electronic circuit element combinations and the biological tissue samples. We analyze the Nyquist plots obtained from the EIS measurements and compare the equivalent circuit parameters calculated by LEBISDI with the corresponding original circuit parameters to assess the accuracy of the program developed. Calibration studies show that LEBISDI not only interpreted the simulated and circuit-element data accurately, but also successfully interpreted tissues impedance data and estimated the capacitive and resistive components produced by the compositions biological cells. Finally, LEBISDI efficiently calculated and analyzed variation in bioimpedance parameters of different tissue compositions, health and temperatures. LEBISDI can also be used for human tissue impedance analysis for electrical impedance-based tissue characterization, health analysis and disease diagnosis.

VISUALIZATION OF BIOLOGICAL TISSUE IMPEDANCE PARAMETERS

Objective. Investigation the opportunity for measurement of biological tissue impedance to visualize its parameters. Materials and methods. Studies were undertook on the experimental facility, consists of registrating measuring cell, constructed from flat inductors system, formed in oscillatory circuit, herewith investigated biological tissue is the part of this oscillatory circuit. An excitation of oscillatory circuit fulfilled by means of exciter inductor which forms impulse complex modulated electromagnetic field (ICM EMF). The measurement process and visualizations provided by set of certificated instruments: a digital oscillograph AKTAKOM ADS-2221MV, a digital generator АКТАКОМ AWG-4150 (both with software) and a gauge RLC E7-22. Comparative dynamic studies of fixed volume and weight pig’s blood, adipose tissue, muscular tissue impedance were conducted by contact versus contactless methods. Contactless method in contrast to contact method gives opportunity to obtain the real morphological visualization of biological tissue irrespective of their nature. Results. Comparison of contact and contactless methods of impedance measurement shows that the inductance to capacitance ratio X(L) / X(C) was equal: 17 – for muscular tissue, 4 – for blood, 1 – for adipose tissue. It demonstrates the technical correspondence of both impedance registration methods. If propose the base relevance of X (L) and X (C) parameters for biological tissue impedance so contactless measurement method for sure shows insulating properties of adipose tissue and high conductivity for blood and muscular tissue in fixed volume-weight parameters. Registration of biological tissue impedance complex parameters by contactless method with the help of induced ICM EMF in fixed volume of biological tissue uncovers the most important informative volumes to characterize morphofunctional condition of biological tissue namely X (L) / X (C). Conclusion. Contactless method of biological tissue impedance measurement is more informative and dynamic and able to mirror morphologic features of organ’s tissue, since it does not depend from electric field divergence lines, electrode polarization and their localization, what takes place during contact method of impedance measurement. Contactless method of biological tissue impedance measurement can be applied as the base diagnostic method – dynamic volumogaraphy.

Electrical Bioimpedance: Methods and Applications

Bio-electrical impedance analysis (BIA) is an inexpensive, quick and noninvasive technique for measuring body composition. Unlike other various complicated methods, bioimpedance measurement technique is simple and less time consuming for various applications including medicine, biotechnology and security system. BIA is a promising method for predicting changes in body composition and has the potential to replace the conventional methods of detection and diagnosis of diseases in near future. The results are reproducible and rapidly obtained. However it suffers from a lack of standardized methods and quality control procedures. This paper describes the theory and practical implementation of various methods to measure complex impedance of biological tissues. By reviewing the current development status of bioimpedance technology, the paper analyses the future emphasis of development and technology direction, in order to make bioimpedance technology gain wider clinical applications.

Classification of normal and cancerous lung tissues by electrical impendence tomography.

Biological tissue impedance spectroscopy can provide rich physiological and pathological information by measuring the variation of the complex impedance of biological tissues under various frequencies of driven current. Electrical Impedance Tomography (EIT) technique can measure the impedance spectroscopy of biological tissue in medical field. Before application, a key problem must be solved on how to generally distinguish normal tissues from the cancerous in terms of measurable EIT data. In this paper, the impedance spectroscopy characteristics of human lung tissue are studied. On the basis of the measured data of 109 lung cancer patients, Cole-Cole Circle radius (CCCR) and the complex modulus are extracted. In terms of the two characteristics, 71.6% and 66.4% samples of cancerous and normal tissues can be correctly classified, respectively. Furthermore, two characteristics of the measured EIT data of each patient consist of a two-dimensional vector and all such vectors comprise a set of vectors. When classifying the vector set, the rate of correctly partitioning normal and cancerous tissues can be raised to 78.2%. The main factors to affect the classification results on normal and cancerous tissues are generally analyzed. The proposed method will play an important role in further working out an efficient and feasible diagnostic method for potential lung cancer patients, and provide theoretical basis and reference data for electrical impedance tomography technology in monitoring pulmonary function.

Novel Transducer for Characterization of Low-Impedance Materials

Piezoelectric materials such as lead-zirconate-titanate (PZT), lead-metaniobate, and piezo-composites are the materials of choice for acoustic imaging in medical diagnosis as well as underwater ultrasonic microphones and underwater sonar. PZT materials have the advantage of having high electro-mechanical coupling, low internal losses and excellent environmental durability. Nonetheless, in order to improve energy transmission the high acoustic impedance of piezoelectric ceramics needs to be matched to the lower acoustic impedance of biological tissues and water. For actuators resonated in their thickness mode, energy transmission can be improved by means of intermediate layers of material of carefully selected thicknesses and acoustic properties. Sometimes a backing layer is also added to the back of the actuator to damp the acoustic back-wave. The process of making these types of transducers is generally costly due to the nature of the manufacturing process and the required level of accuracy. This paper describes an inexpensive method of manufacture low-cost, low-impedance, piezoelectric transducers. The fundamental physical principles behind this new type of sensor-actuator, as well as various examples of imaging low-impedance targets using a prototype of this newly developed sensor-actuator system will be presented.

Short-time chirp excitation for wideband identification of dynamic objects

In this paper, some aspects of choosing excitation signals for fast measurement of complex electrical impedance of objects, including impedance of biological tissues, over a wide range of frequencies are discussed. For this purpose, several short-time excitation signals as special cases of chirp signals of near to minimal duration are proposed. The results of analysis and simulation are promising for implementing such kind of signals as the stimulating ones for fast estimation of bioimpedance parameters.

Assessment of vasomotor oscillations with Fourier analysis of biological tissue impedance

Fourier analysis revealed a number of periodicities in small variations of bioimpedance of human finger including the major spectrum peaks at the frequencies of heart beats, respiration, and Mayer wave (0.1 Hz). These periodic variations of bioimpedance were detected under the normal conditions and during blood flow arrest in the hand by a pneumatic cuff placed on the arm. They are explained by periodic variations in systemic blood pressure and by oscillations of regional vascular tone resulted from neural vasomotor control. During normal blood flow, the greatest variations in bioimpedance were observed at the heart rate, and their amplitude surpassed by an order of magnitude the amplitudes of respiratory oscillations and Mayer wave. In contrast, during blood arrest, the largest amplitude of rhythmical changes of the impedance characterized the oscillations at respiration rate, while the amplitude of oscillations at the heart rate was the smallest. During normal respiration and circulation, two side cardiac peaks were revealed in bioimpedance amplitude spectrum which disappeared during respiration arrest and thought to reflect the amplitude respiratory modulation of the cardiac output via sympathetic influences. During normal breathing, the second and the third harmonics of the cardiac spectrum peak were split reflecting frequency respiratory modulation of the heart rate by parasympathetic influences. The results favour applicability of Fourier analysis of bioimpedance variations in assessment of regional neural influences and neurogenic modulation of cardiac activity.

Solving the forward problem of magnetoacoustic tomography with magnetic induction by means of the finite element method

Magnetoacoustic tomography with magnetic induction (MAT-MI) is a recently proposed imaging modality to image the electrical impedance of biological tissue. It combines the good contrast of electrical impedance tomography with the high spatial resolution of sonography. In this paper, a three-dimensional MAT-MI forward problem was investigated using the finite element method (FEM). The corresponding FEM formulae describing the forward problem are introduced. In the finite element analysis, magnetic induction in an object with conductivity values close to biological tissues was first carried out. The stimulating magnetic field was simulated as that generated from a three-dimensional coil. The corresponding acoustic source and field were then simulated. Computer simulation studies were conducted using both concentric and eccentric spherical conductivity models with different geometric specifications. In addition, the grid size for finite element analysis was evaluated for the model calibration and evaluation of the corresponding acoustic field.

Mechanical impedance of biological tissues in a model with preset displacements on the surface of a half-space

A model is developed to describe the formation of the mechanical impedance of biological tissues for the case where the impedance is measured by pressing a circular flat vibrating disk into the tissue normally to its surface while both the disk and the stationary frame of the measuring device are in contact with the tissue surface. Analytical expressions in quadrature form are derived for the mechanical impedance of tissues by using the model of a half-space with preset displacements of its surface. Numerical calculations are performed, and the agreement with the experiments is demonstrated for the effects caused by the tight contact of the tissue surface with the stationary frame of the measuring device.

Comportamento da impedância elétrica dos tecidos biológicos durante estimulação elétrica transcutânea

OBJECTIVE: To analyze the electrical impedance of biological tissues during electrical stimulation in relation to different segments, surfaces and current frequencies, with increasing distance between electrodes. METHOD: 20 female volunteers of mean age 23 ± 2.25 years and mean body mass index 20.65 ± 1.44 kg/m2 were positioned in decubitus with one electrode placed proximally to the wrist and ankle joint lines, anteriorly and posteriorly, or on the posterosuperior iliac spine, and the other electrode was placed at distance of 10, 20, 30 and 40 cm, sequentially. Two currents (100 us and 10 mA) were applied: one at 100 Hz (LF) and the other at 2000 Hz modulated at 100% of the amplitude for 100 Hz (MF), with a minimum interval of seven days. The impedance was calculated indirectly using Ohm's Law, from the applied intensity and the electrical voltage picked up by a system consisting of a digital oscilloscope (TDS 210, Tektronix®) and a direct current generator (Dualpex 961, Quark®). For statistical analysis, Anova-F and Kruskal-Wallis were applied, with post hoc (SNK), Friedman test and Spearman correlation coefficient, taking p< 0.05. RESULTS: Despite similar electrical impedance behavior with increasing distance between electrodes for the two currents, there was a reduction in impedance under MF stimulation. In the limbs, approximately 50% of the impedance variance was explained by the increase in electrode separation, although this relationship was not observed on the posterior surface of the trunk. Independent of the current type, the trunk presented the lowest electrical impedance, followed by the lower limbs. CONCLUSION: The electrical impedance of the tissues was influenced by current frequency and the positioning and distance between electrodes, thus presenting a non-uniform pattern in the different segments.

Magnetoacoustic tomography with magnetic induction for imaging electrical impedance of biological tissue

An experimental feasibility study was conducted on Magnetoacoustic-Tomography with Magnetic Induction (MAT-MI). It is demonstrated that the 2-dimensional (2D) MAT-MI system can detect and image the boundaries between regions of different electrical conductivity with high spatial resolution. Utilizing a magnetic stimulation coil, MAT-MI evokes magnetically induced eddy current in an object which is placed in a static magnetic field. Because of the existence of Lorenz forces, the eddy current in turn causes acoustic vibrations, which are measured around the object in order to reconstruct the electrical impedance distribution of the object. The present experimental results from the saline and gel phantoms are promising and suggest the merits of MAT-MI in imaging electrical impedance of biological tissue with high spatial resolution.

Device for Intra-Cavity Measurement of Mechanical Impedance of Biological Tissue

Device for Intra-Cavity Measurement of Mechanical Impedance of Biological Tissue

A preliminary study on temperature changemonitoring using the MR current density imaging technique

Based on the fact that the electrical impedance of biological tissues is very sensitive to temperature, we have proposed a method to monitor local temperature changes inside the tissues. Using an analytic model and a finite element method model, we have analysed the effect of the local temperature change on the phase image obtained by the magnetic resonance current density imaging technique. We show preliminary experimental results of the temperature change monitoring performed with a 0.3 T magnetic resonance imaging system. We expect that the proposed method can be utilized for the development of non-invasive temperature imaging techniques.

Simulation of non-contact measurement of the electrical impedance using an anatomical model.

The measurement of the impedance of biological tissue can be a non-invasive method to find new data of diagnostic relevance. A system for a non-contact measurement of the electrical impedance of biological tissue is presented. The system consists of an excitation coil and two sensing coils, an upper and a lower coil. If the two sensing coils are coupled it can be used as a gradiometer coil. Numerical experiments with focus on the eddy currents in the tissue and on the detection of the small changes of the signal are carried out to calculate the fields, eddy current distributions and induced voltages. Hereby tests with different frequencies of the excitation current and different conductivities of a tissue block are used. Then the homogeneous tissue block is replaced with a fraction of the arm of an anatomical model which contains different tissue classes.

New approach to making instruments for measuring the electrical impedance of biological tissues

A new approach to the construction of instruments for measuring the electrical impedance of biological tissues is substantiated. The crux of the method is in the use of an electrical power generator for producing the electrical regime. Consideration is given to problems in the implementation of electrical power generators.

Principles of the impedance technique

A simplified treatment of the electrical impedance of biological tissues is presented, examining the sources of impedance changes and the requirements for recording these changes. The author covers small electrodes, simple models, resistivity of blood, the reactive component in bioimpedance, the use of bioadmittance, the use of the finite-element technique and impedance matching.

Transthoracic electrical impedance at 1 and 100 kHz--a means for separating thoracic fluid compartments?

The electrical impedance of biological tissues varies with their water and electrolyte contents. Alternating current above 5-10 kHz passes both intra- and extracellular fluid, and lower frequency current preferentially extracellular fluid. In an attempt to evaluate thoracic fluid in different compartments, transthoracic electrical impedance (TEI) was measured at 1 and 100 kHz in 15 consecutive patients, without overt left heart failure and under haemodynamic surveillance, during the first two days of myocardial infarction. To achieve different states of hydration the patients were given i.v. furosemide, either 40 mg t.i.d. (high dose group--HDG) or 20 mg once daily (low dose group--LDG). Effects of altered body position and the respective furosemide injections, were evaluated on both days. Mean 24-h-diuresis was 3.9 l in the HDG and 2.5 l in the LDG. After 24 h mean pulmonary arterial diastolic pressure had decreased by 30% in the HDG but remained almost unchanged in the LDG. By then mean basal TEI was increased only in the HDG, by 17% at 1 kHz and 13% at 100 kHz. On Day 1, within one hour after furosemide, TEI increased temporarily by 3-5%, at both frequencies and in both groups. On Day 2, this short-term increase was similar in the LDG at both frequencies and in the HDG at 100 kHz, but not at 1 kHz, consistent with a major extracellular fluid loss in the HDG. TEI at 1 and 100 kHz may thus reflect extracellular and total thoracic fluid, respectively.