Impedance Of Biological Tissues Research Articles

Digitally Controllable Multifrequency Impedance Emulator for Bioimpedance Hardware Validation

ABSTRACTThe accurate emulation of the electrical impedance of biological tissues is crucial for the development and validation of bioimpedance measurement devices and algorithms. This paper describes a digitally controllable impedance emulator capable of reproducing values representative of tissue bioimpedance in user‐specified resistance, reactance, and frequency ranges up to 1 MHz. The presented solution uses a 2R‐1C impedance model to emulate the impedance characteristics of a biological tissue. Specific selection of each element value in this model is achieved using analog multiplexers with low resistance. A MATLAB algorithm was developed for value estimation using target impedance requirements. An example design to emulate impedance from 1 kHz to 1 MHz with 10 to 400 resistance and maximum reactance is provided. The nonideal behavior of this design was evaluated and compared against experimentally collected impedance measurements. Deviations of <1% were observed between experimental and theoretical resistances for values up to 100 kHz (with approximately 5% deviations up to 1 MHz) and reactance deviations were also <1% up to 10 kHz. High frequency deviations are attributed to the parasitic capacitance in the realization of the design. The experimental results validate the design approach and realization for low frequencies. Overall, the innovation of the proposed approach is the control of both resistance and reactance for emulating electrical impedance representative of biological tissues.

Effects of temperature on electrical impedance of biological tissues: ex-vivo measurements.

Bioelectrical impedance techniques have been useful in various applications, including body composition analysis, impedance plethysmography, impedance cardiography, lung ventilation, perfusion, and tissue characterization. Electrical impedance methods have also been useful in characterizing different foods like meat, fruits, and beverages. However, the temperature of tissue samples can change their dielectric properties, affecting their impedance. This research investigated the effects of temperature on the impedance of various biological tissues over the frequency range of 10 Hz to 5 MHz. Freshly excised animal tissues (lamb, cow, chicken), fish, fruits, and plants were considered as biological samples. The samples were placed in a test cell and submerged in a water bath heated by a hot plate to vary the temperature. Impedance measurements were conducted using a bioimpedance spectrometer in 2 °C steps within the temperature range of 20 °C to 50 °C. Impedance values decreased with increased temperature across all measurement frequencies for all biological samples. Curve fitting indicated that impedance decreased linearly with temperature, with a mean correlation coefficient of 0.972 for all samples. For all biological samples under investigation, the relative impedance change ranged from -0.58% to -2.27% per °C, with a mean and standard deviation of (-1.42±0.34) %/°C. On average, animal samples exhibited a higher relative temperature coefficient of -1.56% per °C (±0.41) across the frequency range, compared to -1.31% per °C (±0.26) for fruit and vegetable samples. Additionally, the relative temperature coefficient values were generally higher at lower frequencies than at higher frequencies. The findings of this research can be valuable for studies or biomedical applications involving variable tissue temperatures.

A USAGE OF THE IMPEDANCE METHOD FOR DETECTING CIRCULATORY DISORDERS TO DETERMINE THE DEGREE OF LIMB ISCHEMIA

New engineering technologies allow the creation of diagnostic devices for predicting the development of acute tissue ischemia of the extremities and determining the residual time until the removal of the tourniquet, and solving these tasks is particularly relevant during military actions. Acute limb ischemia is a sudden critical decrease in perfusion that threatens the viability of the limb. The incidence of this condition is 1.5 cases per 10 000 people per year. Acute ischemia occurs due to the blockage of blood flow in major arteries (embolism, thrombosis, trauma), leading to the cessation of adequate blood supply to metabolically active tissues of the limb, including the skin, muscles, and nerve endings. To address these issues, the article analyzes the changes in the impedance of biological tissue. The introduction and use of the coefficient of relative electrical conductivity, denoted as k, as a diagnostic criterion parameter, are justified. Experimental studies of changes in the coefficient of relative electrical conductivity k were conducted, confirming that the transition from exponential to linear dependencies of the coefficient establishes the degree of viability of the biological cell (tissue) and the moment of occurrence of reperfusion syndrome. It has been established that a deviation of the value of k by 10–15% from its unit value diagnoses the initial process of blood perfusion impairment and the development of ischemic tissue disease. The rate of change of k serves as a criterion for predicting the progression of the disease and as a corrective factor for therapeutic treatment.

Early breast cancer detection and differentiation tool based on tissue impedance characteristics and machine learning.

During Basic screening, it is challenging, if not impossible to detect breast cancer especially in the earliest stage of tumor development. However, measuring the electrical impedance of biological tissue can detect abnormalities even before being palpable. Thus, we used impedance characteristics data of various breast tissue to develop a breast cancer screening tool guided and augmented by a deep learning (DL). A DL algorithm was trained to ideally classify six classes of breast cancer based on electrical impedance characteristics data of the breast tissue. The tool correctly predicted breast cancer in data of patients whose breast tissue impedance was reported to have been measured when other methods detected no anomaly in the tissue. Furthermore, a DL-based approach using Long Short-Term Memory (LSTM) effectively classified breast tissue with an accuracy of 96.67%. Thus, the DL algorithm and method we developed accurately augmented breast tissue classification using electrical impedance and enhanced the ability to detect and differentiate cancerous tissue in very early stages. However, more data and pre-clinical is required to improve the accuracy of this early breast cancer detection and differentiation tool.

A fast approach to determine excitation eigenfrequencies for TD-EIT and FD-EIT

Electrical impedance tomography can reconstruct the complex conductivity distribution by injecting a current or voltage at a specific frequency into the target domain. The complex conductivity spectroscopy of numerous biological tissues is frequency-dependent. A suitable excitation frequency is vital to high-quality imaging over a wide frequency range. This paper investigates the relationship between the parameters of the biological tissue impedance model and the impedance spectroscopy. A frequency selection method based on the impedance spectroscopy is proposed, in which the impedance spectroscopy on a specific electrode at the domain boundary to be measured is first scanned. In TD-EIT, the difference between the target’s impedance spectroscopy and the null field is calculated, and the frequency corresponding to its extreme value is used as the excitation signal for TD-EIT. The excitation frequency in FD-EIT is the frequency corresponding to the extreme point in the target impedance spectroscopy, and we have also used this method to image the interior of the maize ear. This study provides a quick and efficient method for determining the excitation frequency for EIT, allowing researchers to find the best excitation frequency for high-quality imaging during actual measurements.

Justification of the electrical scheme of biological tissue replacementunder the action of DC voltage

The change in the impedance of biological tissue under the influence of voltage is used in the diagnosis and treatment of various diseases. Mathematical models describing physical and biological processes in biological objects are based on electrical substitution schemes. The subject of research of this work was the study of the change in the impedance of biological tissue in the transient process of ionization under the action of DC voltage. An analysis of the known substitution schemes was carried out, the shortcomings of their application were identified when the transient processes of ionization in the tissue under the action of direct current voltage were studied, and the substitution scheme with the introduction of additional resistance was substantiated, both analytically and experimentally. In the work, the bioimpedance method is applied when direct current voltage is applied to biological tissue, taking into account the law of commutation in transient ionization processes. An invasive measurement of the change in impedance with needle electrodes was carried out, and it was proved that the active component proportionally depends on the distance between the electrodes, while the capacitive component remains unchanged. It is shown that the ionization time constant is a criterion parameter and can be used in the diagnosis of the development of ischemic disease of muscle tissue, the change in the state of biological tissue when blood flow is stopped during the application of a tourniquet. It has been proven that the ionization time constant does not change with an unchanged ionic composition of the tissue and can be used in the analysis of the composition of the intercellular space. A simultaneous invasive measurement was performed in two identical places of different limbs, on one of which a hemostatic tourniquet was applied. The obtained results made it possible to conclude that a change in the constant time from 15% to 50% compared to two constant times allows for rapid diagnosis, within 2 minutes, of the state of biological tissue and can be used in the study of the development of diseases associated with ischemia. The results of the study can be used for rapid diagnosis of the state of a biological object and the creation of an inexpensive device for its use in surgery and research laboratories

Fluorine-containing ferroelectric polymers: applications in engineering and biomedicine

Highly polar fluorine-containing ferroelectric polymers based on vinylidene fluoride refer to the class of electroactive polymers suitable for various engineering applications. Under usual crystallization conditions, polycrystalline texture is formed, while after high-voltage polarization, it is transformed into a non-centrosymmetric structure, which gives rise to high piezoelectric and pyroelectric responses. Such materials can be used for pyroelectric energy conversion. Owing to high impact strength, ferroelectric polymers can serve as materials for alternative energy sources that convert dynamic impact energy into electricity. The non-linearity of electric response (owing to ferroelectricity) and high breakdown fields offer opportunity of using them in capacitive charge storage devices. The intense dynamics of the amorphous phase provides a rapid discharge of the stored energy into an external circuit. In view of the considerable fraction of the amorphous phase ( 50%) in fluorine-containing ferroelectric polymers and high dielectric permittivity of the amorphous phase, it is possible to change the system entropy by applying an electric field. In the case of pulsed field, this provides a temperature drop; therefore, these materials (especially as composites) are promising for the design of solid-state refrigerators. The high thermoplasticity of these polymers is useful for the design of sensors <i>e.g.</i>, microphones) with a patterned active membrane surface and enhanced characteristics. Biocompatibility and low acoustic impedance (close to the impedance of biological tissues) accounts for the possibility of using these polymers as biosensors. When domains are present in a ferroelectric film, strong local electric fields appear, which can affect the activity of living cells. Using the direct and reverse piezoelectric effect, it is possible to stimulate and control the functions of various tissues, including the nervous tissue. <br> The bibliography includes 463 references.

Comparison of the performance and reliability between improved sampling strategies for polynomial chaos expansion.

As uncertainty and sensitivity analysis of complex models grows ever more important, the difficulty of their timely realizations highlights a need for more efficient numerical operations. Non-intrusive Polynomial Chaos methods are highly efficient and accurate methods of mapping input-output relationships to investigate complex models. There is substantial potential to increase the efficacy of the method regarding the selected sampling scheme. We examine state-of-the-art sampling schemes categorized in space-filling-optimal designs such as Latin Hypercube sampling and L1-optimal sampling and compare their empirical performance against standard random sampling. The analysis was performed in the context of L1 minimization using the least-angle regression algorithm to fit the GPCE regression models. Due to the random nature of the sampling schemes, we compared different sampling approaches using statistical stability measures and evaluated the success rates to construct a surrogate model with relative errors of <0.1%, <1%, and <10%, respectively. The sampling schemes are thoroughly investigated by evaluating the y of surrogate models constructed for various distinct test cases, which represent different problem classes covering low, medium and high dimensional problems. Finally, the sampling schemes are tested on an application example to estimate the sensitivity of the self-impedance of a probe that is used to measure the impedance of biological tissues at different frequencies. We observed strong differences in the convergence properties of the methods between the analyzed test functions.

Short-Time Impedance Spectroscopy Using a Mode-Switching Nonsinusoidal Oscillator: Applicability to Biological Tissues and Continuous Measurement.

Herein, we propose an impedance spectroscopy method using a mode-switching nonsinusoidal oscillator and apply this method for measuring the impedance of biological tissues and continuous impedance measurement. To obtain impedance spectra over a wide frequency range, we fabricated a novel nonsinusoidal oscillator incorporating binary counters and analog switches. This oscillator could periodically switch oscillation frequency through the mode switching of the feedback resistor. From the oscillation waveform at each oscillation frequency of this circuit (oscillator), we determined the impedance spectrum of a measured object using the discrete-time Fourier transform. Subsequently, we obtained the broad impedance spectrum of the measured object by merging odd-order harmonic spectral components up to the 19th order for each oscillation frequency. From the measured spectrum, the resistive and capacitive components of the circuit simulating bioimpedance were estimated with high accuracy. Moreover, the proposed method was used to measure the impedance of porcine myocardium; changes in the impedance spectrum of the myocardial tissue due to coagulation could be measured. Furthermore, rapid variations in the resistance value of a CdS photocell could be continuously measured using the proposed method.

Ex-Vivo Detection of Breast Cancer with a Bio-Impedance Sensor

Bioimpedance is the opposition to flow of an applied electrical current through biological tissues1. Our research group designed and fabricated bipolar micro-sensors on the tip of a silicone probe, capable of measuring biological tissue impedance. It is known that the bioimpedance of cultured cancer cells differs substantially from that of healthy cell lines. We hypothesised that the bioimpedance of cancer in surgically excised human tissue would be significantly different to surrounding healthy tissue. To test this hypothesis, we designed a study to evaluate the bioimpedance of healthy and diseased breast tissue in surgically excised breast specimens. This manuscript reports the outcome of this study.

Investigation of frequency characteristics of biological tissues impedance

The problem of identifying informative signs of biological tissues viability using the impedance measurement method is formulated. At present there is no instrumental base that makes it possible in an operational setting to diagnose the ability of biological tissue to heal itself after injury and damage as a result of thermal exposure, gunshot wound or prolonged compression. It is shown in this article that development of methods and tools for instrumental diagnostics in medical diagnostic practice is an important modern challenge.&#x0D; The results of experimental measurements of impedance characteristics in the frequency range of 20 Hz – 2.0 MHz are presented. The frequency dependences of the modulus of voltage on biological tissues of plant origin are analyzed in its intact state, as well as after exposure of biological tissue samples in a freezer at time intervals from 15 minutes to 2 hours.&#x0D; A comparative analysis of the obtained frequency dependences is carried out. A significant difference between the frequency dependences of the voltage modulus on biological tissues and the frequency dependence of the voltage modulus on an isotonic solution is shown. The concept is introduced that the degree of difference between the frequency distribution of the biological tissue impedance module from the impedance module of an isotonic solution can serve as a criterion for assessing the degree of damage to biological tissue.&#x0D; A conclusion is made about the advisability of developing the impedance measurement method as a method for diagnosing the viability of biological tissue; it is shown that the most promising approach to the development of impedance measurement methods is the analysis of transient processes when biological tissue is disturbed by small electric current pulses.

A Comparative Study of Two Fractional-Order Equivalent Electrical Circuits for Modeling the Electrical Impedance of Dental Tissues.

Background: Electrical impedance spectroscopy (EIS) is a fast, non-invasive, and safe approach for electrical impedance measurement of biomedical tissues. Applied to dental research, EIS has been used to detect tooth cracks and caries with higher accuracy than visual or radiographic methods. Recent studies have reported age-related differences in human dental tissue impedance and utilized fractional-order equivalent circuit model parameters to represent these measurements. Objective: We aimed to highlight that fractional-order equivalent circuit models with different topologies (but same number of components) can equally well model the electrical impedance of dental tissues. Additionally, this work presents an equivalent circuit network that can be realized using Electronic Industries Alliance (EIA) standard compliant RC component values to emulate the electrical impedance characteristics of dental tissues. Results: To validate the results, the goodness of fits of electrical impedance models were evaluated visually and statistically in terms of relative error, mean absolute error (MAE), root mean squared error (RMSE), coefficient of determination (), Nash–Sutcliffe’s efficiency (NSE), Willmott’s index of agreement (WIA), or Legates’s coefficient of efficiency (LCE). The fit accuracy of proposed recurrent electrical impedance models for data representative of different age groups teeth dentin supports that both models can represent the same impedance data near perfectly. Significance: With the continued exploration of fractional-order equivalent circuit models to represent biological tissue data, it is important to investigate which models and model parameters are most closely associated with clinically relevant markers and physiological structures of the tissues/materials being measured and not just “fit” with experimental data. This exploration highlights that two different fractional-order models can fit experimental dental tissue data equally well, which should be considered during studies aimed at investigating different topologies to represent biological tissue impedance and their interpretation.

Biohybrid Soft Robots, E-Skin, and Bioimpedance Potential to Build Up Their Applications: A Review

Soft Robotics is a new approach towards better human-robot interaction and biomimicry in the robotics field. Its integration with biological materials (Biohybrid soft robotics) is one of the topics being focused on in the soft robotics research in the last fifteen years. The motive for this approach is to combine the best of biological and artificial systems. In this article, Biohybrid soft robots and Electronic Skin (E-skin), which is considered one of the advances of soft robotics, are reviewed. Their most significant milestones and the highlights of their most researched applications are listed. Bioimpedance, which is the impedance of biological tissue to an applied AC signal, has been used recently in many agriculture and medical applications for its non-destructive nature. It has been used in many bio-related applications for its ability to assess the state of living tissues. However, it has not been applied in biohybrid soft robots yet. Bioimpedance equivalent electrical models are surveyed showing both integer and fractional order based models. Finally, its potential to enhance biohybrid soft robotics and e-skin applications is discussed and validated.

Very Low Resource Digital Implementation of Bioimpedance Analysis.

Bioimpedance spectroscopy consists of measuring the complex impedance of biological tissues over a large frequency domain. This method is particularly convenient for physiological studies or health monitoring systems. For a wide range of applications, devices need to be portable, wearable or even implantable. Next generation of bioimpedance sensing systems thus require to be implemented with power and resource savings in mind. Impedance measurement methods are divided into two main categories. Some are based on “single-tone” signals while the others use “multi-tone” signals. The firsts benefit from a very simple analysis that may consist of synchronous demodulation. However, due to necessary frequency sweep, the total measurement may take a long time. On the other hand, generating a multi-frequency signal allows the seconds to cover the whole frequency range simultaneously. This is at the cost of a more complex analysis algorithm. This makes both approaches hardly suitable for embedded applications. In this paper, we propose an intermediate approach that combines the speed of multi-tone systems with a low-resource analysis algorithm. This results in a minimal implementation using only adders and synchronous adc. For optimal performances, this small footprint digital processing can be synthesized and embedded on a mixed-mode integrated circuit together with the analog front-end. Moreover, the proposed implementation is easily scalable to fit an arbitrary frequency range. We also show that the resulting impact on noise sensitivity can be mitigated.

The calculation of the impedance of biological tissue on the model of Yamamoto in the process of galvanic effects

The purpose of this work is to improve the accuracy of research related to the work in the field of modeling and measurement of galvanic processes in biological tissues under the influence of electric current. For this purpose, we propose a refined equivalent electrical model of biotissue and an algorithm for numerical determination of its components.

Residual impedance effect on emulated bioimpedance measurements using Keysight E4990A precision impedance analyzer

The passive electrical properties of a biological tissue, often referred to as the tissue bioimpedance, can be measured using a range of commercially available impedance analyzers. Using commercially available equipment reduces the time to collect measurements and does not require investigators to have the necessary expertise to design and fabricate custom equipment. However, the test configurations to collect the bioimpedance during tissue measurements introduces residual impedances resulting from the tissue/electrode interface and electrode placements. The presence of these residual impedances can influence the accuracy of the collected measurements and impact the range of frequencies that can be reliably measured. This work presents a systematic study of the effect of residual impedances ranging from 1 Ω to 10 kΩ on the accuracy of impedance measurements representative of bioimpedance applications using a Keysight E4990A impedance analyzer. Additionally, experimental data from measurements of a 2R-C model that emulates a biological tissue impedance displays <1% and <5% relative differences for the resistance and reactance, respectively, from 10 kHz to 100 kHz in configurations with residual impedances <1 kΩ and for residual impedances emulating the tissue/electrode interface.

Fatigue-Induced Cole Electrical Impedance Model Changes of Biceps Tissue Bioimpedance

Bioimpedance, or the electrical impedance of biological tissues, describes the passive electrical properties of these materials. To simplify bioimpedance datasets, fractional-order equivalent circuit presentations are often used, with the Cole-impedance model being one of the most widely used fractional-order circuits for this purpose. In this work, bioimpedance measurements from 10 kHz to 100 kHz were collected from participants biceps tissues immediately prior and immediately post completion of a fatiguing exercise protocol. The Cole-impedance parameters that best fit these datasets were determined using numerical optimization procedures, with relative errors of within approximately ± 0.5 % and ± 2 % for the simulated resistance and reactance compared to the experimental data. Comparison between the pre and post fatigue Cole-impedance parameters shows that the R ∞ , R 1 , and f p components exhibited statistically significant mean differences as a result of the fatigue induced changes in the study participants.

Toward a magnetic resonance electrical impedance tomography in ultra-low field: A direct magnetic resonance imaging method by an external alternating current

Measuring the electrical impedance of biological tissues in a low frequency range is challenging. Here, we have conducted a superconducting quantum interference device-based microtesla magnetic resonance (MR) imaging study. To obtain an MR image caused by an injected alternating current (ac), we utilized the direct resonance method in which the nuclear spins resonate with the ac magnetic field generated by the external ac current. This method requires an adiabatic pulse and non-adiabatic step-down pulse techniques. The experimental and simulation results agree well with each other and show the feasibility of low-frequency magnetic resonance electrical impedance tomography in the kHz range.

Accuracy enhancement in low frequency gain and phase detector (AD8302) based bioimpedance spectroscopy system

Bioimpedance spectroscopy (BIS) is the measurement of the impedance of biological tissues. In the development of a low cost, portable BIS system the gain and phase difference detection (GPD) method is usually used. However this method suffers from low accuracy at low frequencies due to the presence of spikes or peaks. Detection and removal of these peaks will improve the performance of the GPD based BIS system at low frequencies. Peak detection in physiological signals is a well developed area. A lot of algorithms have been developed in the past for the determination of peaks in signals and their time of occurrence. For real-time processing, microcontroller based peak detection algorithms have also been developed in the past. In this paper, the problem of the GPD method at low frequency is examined closely and then three algorithms were used to mitigate it. The first is based on a moving average filter, the second is a simple peak detection and elimination (SPD) and the last is a peak detection based on the frequency of the input signal to the GPD (SFPD). These algorithms were evaluated with both simulated and measured data. Four parameters were used to indicate the performance of the algorithms; run-time, RMSE, sensitivity and positive predictability. The RMSEs were less than 0.17 for moving average, 0.07 for SPD and 0.08 for SFPD. The run-times was less than 10 ms for SFPD while that for the SPD and moving average were around 30 ms and 80 ms respectively. In all it was found that the algorithms based on peak detection have better results. The computational simplicity of the algorithms makes them suitable for microcontroller based implementation.

Correction of the Output Parameters of an Electrosurgical Unit for Minimizing Thermal Damage to Tissues

A method for diminishing electrosurgery-induced thermal damage to biological tissues by correcting the power output is considered. The output power is corrected according to the type of biological tissue and the impedance increment caused by coagulation. The results of a study of biological tissue impedance substantiating the feasibility of this method are presented.