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Abstract

In recent years, the degree of spread of osteoporosis in men and women has increased considerably. According to the existing statistics 20 percent of women above the age 50 are suffering from osteoporosis and the degree of its growth has been more among men rather than women. In the following research, a three-dimensional electrical computer model of cancellous bone tissue has been presented which consists of a unit cell made of cortical bone where we adjust the amount of bone density as desired. Using a commercial electromagnetics simulation software, we put the intended piece under the effect of electric field and calculate the electric current and extract the impedance of the tissue. Considering the fact that the electrical properties of the components of the intended piece is different for each frequency, the obtained impedance would be variable with frequency. Changes of the impedance caused by alteration of the bone density, can thus be computationaly estimated and leads to a model-based estimation of impedance sensitivity to changes in bone density. Consequently, it would be advantageous to find a frequency range that causes the highest relative change in the amount of the impedance as bone density is varied. The obtained results in a wide frequency range of 1 kHz – 1 GHz indicated that by the alteration of the bone density from 10 to 30 percent, the highest sensitivity in the electrical properties of cancellous bone occurres at frequencies less than 100 kilohertz.

Abstract

A finite difference model of a four-electrode tissue conductivity measurement system was developed and shown to be within 10% of theory. The model is useful for explaining the behavior of conductivity measurement electrodes in tissue.

Abstract

An animal model of deep brain stimulation (DBS) was used in in vivo studies of the encapsulation process of custom-made platinum/iridium microelectrodes in the subthalamic nucleus of hemiparkinsonian rats via electrical impedance spectroscopy. Two electrode types with 100-μm bared tips were used: i) a unipolar electrode with a 200-μm diameter and a subcutaneous gold wire counter electrode and ii) a bipolar electrode with two parallelshifted 125-μm wires. Miniaturized current-controlled pulse generators (130 Hz, 200 μA, 60 μs) enabled chronic DBS of the freely moving animals. A phenomenological electrical model enabled recalculation of the resistivity of the wound tissue around the electrodes from daily in vivo recordings of the electrode impedance over two weeks. In contrast to the commonly used 1 kHz impedance, the resistivity is independent of frequency, electrode properties, and current density. It represents the ionic DC properties of the tissue. Significant resistivity changes were detected with a characteristic decrease at approximately the 2nd day after implantation. The maximum resistivity was reached before electrical stimulation was initiated on the 8th day, which resulted in a decrease in resistivity. Compared with the unipolar electrodes, the bipolar electrodes exhibited an increased sensitivity for the tissue resistivity.

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.

Abstract

Heart failure is a chronic disease marked by frequent hospitalizations due to pulmonary fluid congestion. Monitoring the thoracic fluid status may favor the detection of fluid congestion in an early stage and enable targeted preventive measures. Bioelectrical impedance spectroscopy (BIS) has been used in combination with the Cole model for monitoring body composition including fluid status. The model parameters reflect intracellular and extracellular fluid volume as well as cell sizes, types and interactions. Transthoracic BIS may be a suitable approach to monitoring variations in thoracic fluid content.

Abstract

The electrical impedance method of peripheral vein detection is a novel approach, which offers the advantages of not being expensive and the capability of minimizing and reducing the difficulty of achieving intravenous access in many patients, especially pediatric and obese patients. The electrical impedance method of peripheral vein detection is based on the measurement of electrical impedance using the 4-electrode technique by applying a known alternating current of frequency 100 kHz and constant amplitude to a set of current electrodes and measuring the resulting surface potential at two separate electrodes. This paper presents the results of investigations to estimate the efficiency of this method.

Abstract

This work presents a simulation analysis of the bioimpedance measurements at the human forearm. The Ansys® High Frequency Structure Simulator (HFSS) has been used to analyze the electrical response of a section of human forearm with three domains of dielectric behavior – fat, muscle and artery (blood). The impedance values were calculated as the ratio of the output voltage at the electrodes to the applied known current (1 mA). A model was developed and was simulated for impedance values obtained within a frequency range of 1 kHz to 2 MHz. The measurements were done at three instances of radial artery diameter. The maximum resistance and reactance values were calculated as 445 Ω and 178.5 Ω, 356 Ω and 138 Ω, and 368 Ω and 144.3 Ω for diameters 2.3 mm, 2.35 mm, and 2.4 mm respectively. The set of impedance values obtained followed the Cole-plot trend. The results obtained were found to be in excellent agreement with the Cole modelling. The set of values obtained at three different diameters reflected the effect of blood flow on impedance values.

Abstract

Electrical impedance tomography (EIT) is a relatively new imaging technique. It has the advantages of low cost, portability, non-invasiveness and is free from radiation effects. So far, this imaging technique has shown satisfactory results in functional imaging. However, it is not yet fully suitable for anatomical imaging due to its poor spatial resolution. In this paper, we review the basic directions of research in the area of the spatial resolution of the EIT systems. The improvements to the hardware and the software developments are highlighted. Finally, possible techniques to enhance the spatial resolution of the EIT systems using array processing beamforming methods are discussed.

Abstract

This paper describes a new combined impedance plethysmographic (IPG) and electrical bioimpedance spectroscopic (BIS) instrument and software that allows noninvasive real-time measurement of segmental blood flow and changes in intracellular, interstitial, and intravascular volumes during various fluid management procedures. The impedance device can be operated either as a fixed frequency IPG for the quantification of segmental blood flow and hemodynamics or as a multi-frequency BIS for the recording of intracellular and extracellular resistances at 40 discrete input frequencies. The extracellular volume is then deconvoluted to obtain its intra-vascular and interstitial component volumes as functions of elapsed time. The purpose of this paper is to describe this instrumentation and to demonstrate the information that can be obtained by using it to monitor segmental compartment volumes and circulatory responses of end stage renal disease patients during acute hemodialysis. Such information may prove valuable in the diagnosis and management of rapid changes in the body fluid balance and various clinical treatments.