Parasitic Effects on Electrical Bioimpedance Systems: Critical Review.

Parasitic capacitance represents the main error source in measurement systems based on electrical impedance spectroscopy. The capacitive nature of electrodes' impedance in tetrapolar configuration can give origin to phase errors when electrodes are coupled to parasitic capacitances. Nevertheless, reactive charges in tissue excitation systems are susceptible to instability. Based on such a scenario, mitigating capacitive effects associated with the electrode is a requirement in order to reduce errors in the measurement system. A literature review about the main compensation techniques for parasitic capacitance was carried out. The selected studies were categorized into three groups: (i) compensation in electronic instrumentation; (ii) compensation in measurement processing, and (iii) compensation by negative impedance converters. The three analyzed methods emerged as effective against fixed capacitance. No method seemed capable of mitigating the effects of electrodes' capacitance, that changes in the frequency spectrum. The analysis has revealed the need for a method to compensate varying capacitances, since electrodes' impedance is unknown.

Using segmental bioimpedance analysis to estimate soft tissue and chemical composition of retail cuts and carcasses of lambs.

This study evaluated the potential of segmental bioimpedance analysis (SBIA) to estimate the composition of retail cuts and their predictability to infer on the carcass composition in lambs. Leg, rib, shoulder, neck, and loin from thirty-one lamb carcasses were evaluated. A single-frequency bioelectrical impedance analyzer at 50 kHz was used to perform measurements. The models for estimating soft tissue showed the highest accuracy in the retail cuts. Lean and fat weight of the lamb cuts or of the carcasses were predicted with R2 of calibration ranging from 86.6 to 99.1% and from 67.5 to 95.4%, respectively. Segmental bioimpedance analysis is an accurate technology to assess physical and chemical components in retail cuts of lamb. Despite that, shoulder was the most representative cut; all cuts evaluated through SBIA were valuable to estimate the components of the edible portion of lamb carcasses.

Analytical Model for Blood Glucose Detection Using Electrical Impedance Spectroscopy.

Pathogens and adulterants in human feeding consumables can be readily identified according to their electrical properties. Electrical bioimpedance analysis (BIA) has been widely used for body contents characterization, such as blood, urine, lactate, and sweat. If the concentration of glucose in blood alters the electrical properties of the blood medium, then the impedance spectrum obtained by BIA can be used to measure glycemia. For some applications, artificial neural networks allow the correlation of these parameters both impedance and concentration of glucose by means of symbolic and statistical rules. According to our literature review, there is not any physical model that allows the interpretation of the relationship between blood's electrical properties from impedance spectra and the concentration of glucose in blood plasma. This article proposes a simplified physical model for blood electrical conductivity as a function of concentration of glucose, based on Bruggeman's effective medium theory. The equations of this model were obtained considering an insulating phase distribution diffused in a conductive matrix, in which red blood cells are represented by macroscopic insulating nuclei and glucose molecules by microscopic insulating particles. The impedance spectrum for different glucose concentrations (4.0 to 6.8 mmol/L) in a blood sample, published by Kamat Bagul (2014), were compared to the proposed model. The results showed a significant correlation with the experimental data, showing a maximum error of 5.2%. The proposed model might be useful in the design of noninvasive blood glucose monitoring systems.

Determination of maximum noise level in an ECG channel under SURE Wavelet filtering for HRV extraction

Abstract Heart Rate Variability (HRV) is the measure of variation between R-R interbeats, it has been demonstrated to be a good representation of physiological features, especially to the alterations in the Autonomic Nervous System (ANS). Considering the values that compose a HRV distribution are extracted from electrocardiography (ECG), many of the electrical disturbances that affect ECG-based diagnosis can also interfere with the results of the HRV analysis. This paper uses a 30-minute portion of a healthy patient (no arrhythmias detected or annotated) from the MIT-BIH ECG database to analyze the effectiveness of the SURE Wavelet denoising method for extracting the HRV from a progressively noisier ECG channel. Results show that the minimum SNR for reliable HRV extraction under these conditions is approximately 5dB and outlines the exponential behavior of HRV extraction for escalating noise levels in the ECG signal.

Assessing the composition of the soft tissue in lamb carcasses with bioimpedance and accessory measures.

Consumers are demanding additional information to support their decision-making while shopping for meat. In the lamb industry, labelling carcasses with composition information is challenging. This is due to issues with conventional analytical procedures, such as the time spent with determinations and product loss or devaluing due to sampling for analysis. The objective was to evaluate the potential use of bioimpedance analysis (BIA) to determine composition of the soft tissue portion of lamb carcasses. Thirty-one Texel and Ile-de-France crossbreed ram lambs were slaughtered at 20, 26, 32, or 38 kg of body weight. Values of resistance and reactance were collected from hot and cold carcasses, which weighed 12.4 ± 2.99 kg and 11.9 ± 2.94 kg, respectively and measured 53.9 ± 3.25 cm of length. Carcass weight and length were used to calculate other BIA variables such as impedance modulus, phase angle, bioelectrical volume, and both resistive and reactive densities. These variables were used as independent variables to predict the contents of soft tissue, moisture, ash, protein, fat, lean, and crude energy of the carcasses. Multiple regression analyses were carried out to calibrate BIA models. The leave-one-out cross-validation was performed to evaluate precision and accuracy of the BIA technique. Resistive density was the most important BIA variable to predict lamb composition of hot carcasses, which explained 83% to 92% of the variation in composition. In turn, reactive density better predicted lamb carcass composition in cold carcasses, which accounted for 81% to 92% of their variation in carcass composition. In addition, prediction models of the soft tissue portion of lamb carcasses assessed on cold carcasses showed a higher coefficient of determination and smaller root mean square error and Mallows Cp values than hot carcasses. Therefore, BIA has an excellent potential to predict lamb carcass components on either hot as cold carcass; however, higher accuracy was found with cold carcasses in comparison with hot.

Design of Howland Current Sources Using Differential Evolution Optimization.

Howland circuits have been widely used in Electrical Bioimpedance Spectroscopy applications as reliable current sources. This paper presents an algorithm based on Differential Evolution for the automated design of Enhanced Howland Sources according to arbitrary design constraints while respecting the Howland ratio condition. Results showed that the algorithm can obtain solutions to commonly sought objectives, such as maximizing the output impedance at a given frequency, making it a versatile method to be employed in the design of sources with specific requirements. The mathematical modeling of the source output impedance and transconductance, considering a non-ideal operational amplifier, was validated against SPICE simulations, with results matching up to 10 MHz.

Serious game for locomotor rehabilitation of hemiparetic stroke patients / Jogo sério para reabilitação locomotora de pacientes hemiparéticos por acidente vascular cerebral / Juego serio para rehabilitación locomotora de pacientes hemiparéticos por accidente cerebrovascular

Abstract Introduction: Hemiparesis post-stroke usually results in locomotor limitations. As conventional rehabilitation is monotonous, the Serious Games (SG) represents an excellent treatment strategy, allowing to perform physical training in an interesting and enjoyable way. Objective: To evaluate the effects of an exercise program using the SG developed for hemiparetic stroke patients' locomotor rehabilitation. Method: Non-Randomized Controlled Clinical Trial. Twenty-four hemiparetic stroke patients with subacute or chronic stroke (twelve men), mean age of 57.8 ± 10.4 years (injury time of 16.8 ± 19.6 months) participated in the study. The experimental group (n = 16) participated in an exercise program with the SG for lower limb rehabilitation. The control group (n = 8) received conventional treatment (kinesiotherapy). The intervention consisted of sessions twice a week for ten weeks. The following parameters were assessed: muscle strength (dynamometry), spasticity (Modified Ashworth Scale), functional mobility (Timed Up and Go Test - TUGT), and the gait speed (GS). Results: Both groups showed improvements, but the experimental group was better in all the studied variables, the muscular strength of the lower limb paresis and of the quadriceps femoris (p = 0.002; d = 0.7); and for the hamstrings (p < 0.001; d = 1.3), TUGT (p < 0.001; d = 0.4), and GS (p = 0.001; d = 0.4). Conclusion: The exercise program with the SG was useful for the patients treated in this study. The results showed a superiority of the SG regarding the conventional treatment in all the controlled variables. This was probably because of the greater repeatability of the exercises and the increased attention and motivation.

Resumo Introdução: A hemiparesia pós-acidente vascular cerebral (AVC) habitualmente resulta em limitações locomotoras. Como a reabilitação convencional é monótona, os Jogos Sérios (JS) representam uma excelente estratégia de tratamento, permitindo realizar o treinamento físico de forma interessante e prazerosa. Objetivo: Avaliar os efeitos de um programa de exercícios utilizando um JS desenvolvido para reabilitação locomotora de pacientes hemiparéticos pós-AVC. Método: Ensaio Clínico Controlado Não-Randomizado. Participaram do estudo 24 hemiparéticos pós-AVC na fase subaguda ou crônica (12 homens), com idade média de 57.8 ± 10.4 anos (tempo de lesão 16.8 ± 19.6 meses). O grupo experimental (n = 16) participou de um programa de exercícios com JS para reabilitação do membro inferior. O grupo controle (n = 8) recebeu tratamento convencional (cinesioterapia). A intervenção durou 10 semanas, com frequência de duas sessões semanais. Foram avaliados: força muscular (dinamometria), espasticidade (Escala de Ashworth Modificada), mobilidade funcional (Timed Up and Go Test-TUGT) e a velocidade da marcha. Resultados: Ambos os grupos apresentaram melhoras, sendo o grupo experimental superior em todas as variáveis estudadas, destaque para a força muscular do membro inferior parético, para o quadríceps femoral (p = 0.002; d = 0.7) e para os isquiotibiais (p < 0.001; d = 1.3), TUGT (p < 0.001; d = 0.4) e velocidade da marcha (p = 0.001; d = 0.4). Conclusão: O programa de exercícios com o JS foi útil no tratamento dos pacientes envolvidos neste estudo. Os resultados apontaram uma superioridade do JS em comparação ao tratamento convencional em todas as variáveis controladas. Provavelmente isto ocorreu pela maior repetibilidade dos exercícios e aumento da atenção e motivação.

Resumen Introducción: La hemiparesia post-accidente cerebrovascular (ACV) habitualmente resulta en limitaciones locomotoras. Como la rehabilitación convencional es monótona, los Juegos Serios (JS) representan una excelente estrategia de tratamiento, que le permite realizar el entrenamiento físico de forma interesante y placentera. Objetivo: Evaluar los efectos de un programa de ejercicios utilizando un JS desarrollado para rehabilitación locomotora de pacientes hemiparéticos post-ACV. Método: Ensayo Clínico Controlado no aleatorizado. En el estudio, participaron 24 pacientes hemiparéticos post-ACV en la fase subaguda o crónica (12 hombres), con un promedio de edad de 57,8 ± 10,4 años (tiempo de lesión 16,8 ± 19,6 meses). El grupo experimental (n = 16) participó de un programa de ejercicios con JS para rehabilitación del miembro inferior. El grupo de control (n = 8) recibió tratamiento convencional (Kinesioterapia). Se realizaron dos sesiones semanales, durante diez semanas. Se evaluaron: fuerza muscular (dinamometría), espasticidad (Escala de Ashworth modificada) y movilidad funcional (Timed Up and Go Test - TUGT). Resultados: Ambos grupos presentaron mejoras, siendo que el grupo experimental fue superior en todas las variables estudiadas, destaque principalmente para la fuerza muscular del miembro inferior parético, para el cuádriceps femoral (p = 0.002; d = 0.7) y para los isquiotibiales (p < 0.001; d = 1.3), TUGT (p < 0.001; d = 0.4) y velocidad de marcha (p = 0.001; d = 0.4). Conclusión: El programa de ejercicios con el JS fue útil en el tratamiento de los pacientes involucrados en este estudio. Los resultados mostraron una superioridad del JS en comparación con el tratamiento convencional en todas las variables controladas. Probablemente esto ocurrió por la mayor repetibilidad de los ejercicios y aumento de la atención y motivación.

Mirrored enhanced Howland current source with feedback control.

An impedance spectrum is calculated by the ratio between an injecting current and a resulting measured voltage, which allows the extraction of electrical properties from the material under study. The current source is considered an essential block to deliver a controlled current to a wide range of working loads and large bandwidth. To comply with such requirements, the current source output impedance must be much higher than the load impedance at each discrete frequency within the range. However, stray capacitance from cables and circuitry reduce the output impedance, especially at higher frequencies. We proposed a modified mirrored enhanced Howland current source (MEHCS) by using the feedback technique for a wide frequency range applications on electrical bioimpedance. We implemented four MEHCS circuits [with/without multiplexer (MUX) and with/without feedback], and then the output current and impedance were measured up to 20 MHz. The proposed current source showed an improvement in the frequency response at lower and higher frequencies when compared to the standard circuit. The measured output impedance was 10 times higher in the proposed circuit than in the standard MEHCS. The use of a feedback also increased the bandwidth in almost one decade in low and high frequencies when loaded with a resistor of about 1 kΩ.

Extracting Parasite Effects of Electrical Bioimpedance Measurements.

The objective of this work is to develop a technique for filtering parasitic effects from the impedance spectra (IS) measured in biological material phantoms. IS data are contaminated with unexpected capacitive and inductive effects from cable, input/output amplifiers capacitances, electrode polarization, temperature and contact pressure when collecting data. It is proposed a model which contains an RLC-network in series with the Cole model (RSC), then called RLC-Cole. It was built four circuits composed by resistors, capacitors and inductors. An impedance analyzer (HF2IS) was used to perform the measurements in the frequency range of 1 to 3000 kHz. Data were fitted into the model and comparisons to the nominal values were made. In order to validate the proposed model, a gelatin phantom and a chicken breast muscle impedance spectra were also collected and analyzed. After filtering, Cole fitting was performed. Results showed a maximum root-mean-square error of 1% for the circuits, 2.63% for the gelatin phantom, whereas 2.01% for the chicken breast. The RLC-Cole model could significantly remove parasitic effects out of a tissue impedance spectrum measured by a 4-point electrode probe. This may be highly important in EIS systems whose objective is to discriminate a normal tissue from a cancerous one.

Electrical properties of phantoms for mimicking breast tissue.

In order to test and calibrate an EIT (Electrical Impedance Tomography) system, many researchers rely on phantoms mimicking breast tissues. These phantoms are usually made of saline solutions, agar and/or vegetables, allowing the user to set the conductivity of the material by changing the salt concentration. Due to that fact that the dispersion behavior in the vicinity of megahertz is fundamental to detect carcinoma, this work aims to propose a phantom composed by a mixture of agar and gelatin (emulating the normal tissue) and a piece of carrot (emulating the carcinoma). It also investigates the frequency dependence from 1 to 10,000 kHz. The proposed phantom showed capability to mimic some absolute and relative electrical parameters used to detect cancer according to the literature. The differences in the impedance modulus were found to be more dispersive in the mimic carcinoma tissue type than the normal mimic one. It is simple to prepare, low cost, has similar electrical properties to the ones that have been used in the literature, better mechanical properties and longer life time. It can be concluded that gelatin-agar gel may have a high potential to be used as a breast tissue phantom.

Reconhecimento de padrões para classificação da impedância elétrica do tecido cervical / Pattern recognition for electrical impedance classification of cervix tissue / Reconocimiento de padrones para la habilatácion de impedancia eléctrica del tejido cervical

A análise da bioimpedância elétrica de tecidos humanos têm sido utilizada para identificar lesões precursoras ao câncer, auxiliando na prevenção e tratamento precoce. O presente estudo analisou 630 amostras de bioimpedância do tecido cervical de pacientes no estado de Santa Catarina, a fim de identificar lesões no colo do útero. Para tal, comparou-se o desempenho de dois algorítimos de classificação de padrões: Máquina de Vetores de Suporte (SVM) e Redes Neurais (RN) em conjunto com a Análise de Componentes Principais (PCA), separando as amostras entre tecido com lesão ou normal. Ambos classificadores apresentaram resultados satisfatórios. Pode-se concluir que os classificadores de padrões propostos apresentam uma poderosa alternativa para a classificação de tecidos.

The bioelectrical impedance analysis of human tissues have been used to identify early stages of cancer, helpingthe prevention and early treatment. This study analyzed 630 bioimpedance samples of cervical tissue of patients inthe state of Santa Catarina to identify lesions in the cervix. We compared the performance of two pattern recognition algorithms: Support Vector Machines and Neural Networks, in conjunction with Principal Component Analysis, separating the samples of tissue as injured or regular. Both classifiers showed satisfactory results.. It can be concluded that the proposed pattern classifiers might be a powerful alternative tool for tissue characterization.

Numerical sensitivity modeling for the detection of skin tumors by using tetrapolar probe.

The measurement of electrical impedance of skin using surface electrodes permits the assessment of changes in local properties of the skin and can be used in the detection of tumors. The sensitivity of this technique depends mainly on the geometry of the probe and the size of the tumor. In this article, the impedance method was used to estimate the sensitivity of a tetrapolar probe in detecting small regions of increased conductivity in a stratified model of human skin. The impedance method was used to model the potential distribution using fasorial analysis to solve the node equations of the equivalent circuit. Interpolation was applied to reduce discretization error. The skin was modeled as a three-layer structure with different conductivity and permittivity obtained from the literature. A tumor was modeled as a small volume with admittivity four times higher than the normal tissue. Sensitivity calculation was made as a function of electrode diameter and separation, tumor size, and excitation frequency. The simulations indicated that by inserting a one square millimeter tumor in the epidermis, the load impedance to the current source varies about 1% while the transfer impedance varied 8%. The sensitivity also increases nonlinearly with increasing tumor area and thickness. Additionally, it was found that the sensitivity of the transfer impedance has a maximum value when the electrodes are separated by 1.8 mm. The results show that transfer impedance measurements of the skin may detect small skin tumors with a reasonable sensitivity by using an appropriate tetrapolar probe.

Frequency-domain reconstruction of signals in electrical bioimpedance spectroscopy.

The use of an amplitude/phase retrieval algorithm in electrical bioimpedance spectroscopy (EIS) that allows a new technique to reconstruct the impedance spectrum in the frequency-domain is reported. To the authors' knowledge this is the first time the proposed algorithm has been used to calculate the modulus or phase of a bioimpedance in EIS from one of these two experimentally obtained parameters. The algorithmic technique is demonstrated in EIS, when wide-bandwidth amplifiers,phase-detectors, and high speed converters determine spectra over frequencies up to 500 kHz at isolated points in the frequency interval. Simulated data from bioimpedance models (Cole and 2R1C circuit impedance functions) and experimental data from a known electrical impedance are used to show the applicability and limitations of the technique with a phase retrieval and a modulus retrieval algorithm.Results comparing this technique with the Kramers-Kronig technique that retrieves the imaginary part of an impedance from its real part are also discussed.

Stand-off electrode (SoE): a new method for improving the sensitivity distribution of a tetrapolar probe.

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.