DEVELOPMENT OF ELECTRICAL RESISTANCE TOMOGRAPHY (ERT) DATA ACQUISITION PROTOCOLS FOR CONDUCTIVE MULTIPHASE PROCESSES

This report describes a considerably low-cost improvement theory of existing data acquisition system for a 16-electrode Electrical Resistance Tomography (ERT). It comprises of electrical parts such as voltage measurement amplifier circuit and switching circuit. Quality of data acquired is crucial for future work of image processing which induced the importance of mentioned circuits. Experimentations are conducted on brine solution with different concentrations to classify lower and upper range of voltages for different applications as well as demonstrating the effect of different measurement protocols towards common mode voltages

Implementation of a low cost prototype for electrical impedance tomography based on the integrated circuit for body composition measurement AFE4300

Electrical impedance tomography (EIT) is a technique of image reconstruction of the electrical conductivity distribution in a tissue or region under observation. An electrical system for EIT comprises complex hardware and software modules, which are designed for a specific application which requires that the system to be able to detect conductivity variations within the study object. The Front-End for body composition measurement, AFE4300 from Texas Instruments allows a minimal implementation of an electrical impedance tomography system. It is the main device in the development of the EIT system presented in this paper, this device injects the current signal and measures the tensions generated on the study region boundary by 8 electrodes, the image reconstruction software was developed on the National Instruments platform Labview. The system includes a microcontroller PIC16F886 to configure the 8 channels for the definition of the patterns of injection and measurement of signals, also defines the current signal frequency and the bluetooth communication with the computer for the image reconstruction. The developed system was validated by a planar resistive phantom (CardiffEIT phantom), obtaining a stable voltage measurement every 50 ms per pair of electrodes, and a signal to noise ratio (SNR) maximum of 71.8 dB, for a current signal of 50 kHz. Additionally, tests were carried out in a saline tank with a concentration of 4 g/L, the developed system can simultaneously estimate the presence of conductive and non-conductive disturbances into the tank. CopyrightPeer ReviewedPostprint (published version

SYSTEM AKWIZYCJI DANYCH W ELEKTRYCZNEJ TOMOGRAFII IMPEDANCYJNEJ

This article presents the design of the device with active electrodes to examine the flood embankment. There was discussed the method of determining the conductivity. The presented solution was based on electrical impedance tomography. There was described the concept of active electrodes and measuring equipment for data acquisition. Electrical impedance tomography, which is based on measuring potential difference, can be used to calculate conductivity. The problem depends on the fact that every material has unique conductance.W tym artykule przedstawiono konstrukcję urządzenia z aktywnymi elektrodami do badania stanu wału przeciwpowodziowego. Omówiono metodę wyznaczania konduktywności. Prezentowane rozwiązanie zostało oparte na elektrycznej tomografii impedancyjnej. Opisano koncepcję aktywnych elektrod i sprzętu pomiarowego do akwizycji danych. Elektryczna tomografia impedancyjna, która jest oparta na pomiarze różnicy potencjałów może być użyta do pomiaru konduktywności. Sposób, w jaki może być zdefiniowany polega na tym, że każdy materiał ma unikalną przewodność

Anisotropy in Diffusion and Electrical Conductivity Distributions of TX-151 Phantoms

abstract: Among electrical properties of living tissues, the differentiation of tissues or organs provided by electrical conductivity is superior. The pathological condition of living tissues is inferred from the spatial distribution of conductivity. Magnetic Resonance Electrical Impedance Tomography (MREIT) is a relatively new non-invasive conductivity imaging technique. The majority of conductivity reconstruction algorithms are suitable for isotropic conductivity distributions. However, tissues such as cardiac muscle and white matter in the brain are highly anisotropic. Until recently, the conductivity distributions of anisotropic samples were solved using isotropic conductivity reconstruction algorithms. First and second spatial derivatives of conductivity (∇σ and ∇2σ ) are integrated to obtain the conductivity distribution. Existing algorithms estimate a scalar conductivity instead of a tensor in anisotropic samples. Accurate determination of the spatial distribution of a conductivity tensor in an anisotropic sample necessitates the development of anisotropic conductivity tensor image reconstruction techniques. Therefore, experimental studies investigating the effect of ∇2σ on degree of anisotropy is necessary. The purpose of the thesis is to compare the influence of ∇2σ on the degree of anisotropy under two different orthogonal current injection pairs. The anisotropic property of tissues such as white matter is investigated by constructing stable TX-151 gel layer phantoms with varying degrees of anisotropy. MREIT and Diffusion Magnetic Resonance Imaging (DWI) experiments were conducted to probe the conductivity and diffusion properties of phantoms. MREIT involved current injection synchronized to a spin-echo pulse sequence. Similarities and differences in the divergence of the vector field of ∇σ (∇2σ) among anisotropic samples subjected to two different current injection pairs were studied. DWI of anisotropic phantoms involved the application of diffusion-weighted magnetic field gradients with a spin-echo pulse sequence. Eigenvalues and eigenvectors of diffusion tensors were compared to characterize diffusion properties of anisotropic phantoms. The orientation of current injection electrode pair and degree of anisotropy influence the spatial distribution of ∇2σ. Anisotropy in conductivity is preserved in ∇2σ subjected to non-symmetric electric fields. Non-symmetry in electric field is observed in current injections parallel and perpendicular to the orientation of gel layers. The principal eigenvalue and eigenvector in the phantom with maximum anisotropy display diffusion anisotropy.Dissertation/ThesisMasters Thesis Bioengineering 201

Electronic instrumentation for a 3D electrical impedance tomography application

The thesis aims to present the electronic instrumentation required for an EIT application which aims to make an imaging reconstruction of living cells covered with blank hydrogel. Thus the accuracy of the impedance measurement along the frequency range will have a great importance. The experiments performed are made for a 2D EIT system which allows us to extract useful information for the development of the future 3D system. The thesis is divided into four parts: a theoretical study about the bioimpedance and the EIT, the measurement setup used during the course of the thesis and the possible alternatives, the presentation of the results obtained, discussion of results and the conclusion of the thesis. The HF2IS Impedance Spectroscopy (Zurich Instruments AG, Switzerland) is the measurement equipment used to perform four-terminal impedance measurements. The spectroscopy is located in the laboratory of the BioMediTech Group at FinMedi. A multiplexing system has been designed, consisting of four 16x1 channels multiplexers which will be controlled by the digital outputs of the spectroscopy. Besides, the electronic instrumentation required for the EIT system without the HF2IS spectroscope is presented as an aid to future stages of the project

Hacia la construcción de un Tomógrafo de Impedancia Eléctrica (EIT) para la zona del antebrazo humano

Proyecto de Investigación (Código: VIE-180181) Instituto Tecnológico de Costa Rica. Vicerrectoría de Investigación y Extensión (VIE). Escuela de Física, Escuela de Ingeniería Electrónica, 2017La tomografía por impedancia eléctrica (EIT) es una técnica que permite crear imágenes de tejidos humanos a partir de mediciones de impedancia con arreglos de electrodos colocados sobre la superficie de la piel. Al ser un método no invasivo de costo relativamente bajo, importantes esfuerzos de investigación se han realizado con el fin de desarrollar esta técnica en diversas aplicaciones de diagnóstico médico. Tradicionalmente este sistema se aplica a tejidos cuya estructura de conductividades cambia en el tiempo, aplicaciones de esta tecnología son mediciones del volumen de sangre eyectado del corazón, monitorización del volumen de aire que entra y sale de los pulmones y la evolución de accidentes cerebro vasculares. En el caso específico donde la diferencia de conductividad eléctrica permite un alto contraste de los tejidos se ha aplicado como un método de seguimiento de evolución del paciente, pero no de forma exclusiva, este es el caso del cáncer mamario. Este estudio plantea estudiar la factibilidad de desarrollar un tomógrafo de impedancia eléctrica para la zona del antebrazo humano en el Instituto Tecnológico de Costa Rica (ITCR), en cooperación con la Universidad Técnica de Hamburgo (TUHH), y con el fin de complementar a futuro actividades de investigación paralelas en el campo de la estimulación eléctrica neuromuscular. El trabajo realizado muestra la posibilidad de construir un tomógrafo de impedancia eléctrica (EIT) en el Tecnológico, con aplicaciones en sistemas invariantes en el tiempo, como lo es el antebrazo humano; sin embargo, se requiere un refinamiento de las técnicas de reconstrucción de imágenes para lograr la resolución suficiente para localizar tejidos nerviosos, debido principalmente al bajo contraste que presenta este tejido con el medio que lo rode

Estimating the Volume of Unknown Inclusions in an Electrically Conducting Body with Voltage Measurements

We propose a novel technique to estimate the total volume of unknown insulating inclusions in an electrically conducting body from voltage measurements. Unlike conventional Electrical Impedance Tomography (EIT) systems that usually exhibit low spatial resolution and accuracy, the proposed device is composed of a pair of driving electrodes which, supplied with a known sinusoidal voltage, create a current density field inside a region of interest. The electrodes are designed to generate a current density field in the region of interest that is uniform, to a good approximation, when the inclusions are not present. A set of electrodes with a polygonal geometry is used for four-wires resistance measurements. The proposed technique has been tested designing a low cost prototype, where all electrodes are on the bottom of the conducting body, showing good performances. Such a device may be used to monitor the volume of biological cells inside cell culture dishes or the volume of blood clots in micro-channels in lab-on-a-chip biosensor

Towards the development of an EIT-based stretchable sensor for multi-touch industrial human-computer interaction systems

In human-computer interaction studies, an interaction is often considered as a kind of information or discrete internal states of an individual that can be transmitted in a loss-free manner from people to computing interfaces (or robotic interfaces) and vice-versa. This project aims to investigate processes capable of communicating and cooperating by adjusting their schedules to match the evolving execution circumstances, in a way that maximise the quality of their joint activities. By enabling human-computer interactions, the process will emerge as a framework based on the concept of expectancy, demand, and need of the human and computer together, for understanding the interplay between people and computers. The idea of this work is to utilise touch feedback from humans as a channel for communication thanks to an artificial sensitive skin made of a thin, flexible, and stretchable material acting as transducer. As a proof of concept, we demonstrate that the first prototype of our artificial sensitive skin can detect surface contacts and show their locations with an image reconstructing the internal electrical conductivity of the sensor

Electrical Impedance Tomography

Abstract Three-dimensional Electrical Impedance Tomography (EIT) is a technique that has the potential to provide estimates of reservoir saturation at multiple scales by determining the resistivity distribution within the subsurface. In theory EIT is well suited for researching geothermal systems due to the large contrast in resistivity between the liquid and vapor phases. Here in our initial laboratory investigation we have applied the EIT technique to measure the saturation distribution within a core. The initial EIT experiment presented here used a Berea sandstone core with 48 electrodes attached in three rings of 16. The core was open to the atmosphere with saturation occurring by natural imbibition and desaturation by evaporation. The voltage potential field was measured by applying a direct current pulse across the core and measuring the voltage potential at all electrodes, essentially applying the 4-wire resistance technique over all electrodes in turn. The result was a data set that embodies the resistivity distribution within the core, and by inversion the resistivity distribution was reconstructed, which allowed for the inference of the saturation. The data processing was accomplished by utilizing the EIDORS toolkit which was developed for application to this nonlinear and ill-posed inverse problem. The procedure utilizes a finite element model for forward calculation and a regularized nonlinear inverse solver to obtain a unique and stable inverse solution . Experiments have indicated EIT is a viable technique for studying the displacement characteristics of fluids with contrasting resistivity, and is capable of detecting displacement fronts in near real-time. The current system is also a quantitative technique able to measure saturation distributions accurately between 20% < S w < 65%. These limitations were imposed due to connate water connections to the electrodes and ion mobility effects caused by the DC voltage source. It is anticipated that the applicability of EIT will increase to S w = 100% with the implementation of an AC voltage source. vii Acknowledgments First and foremost I would like to sincerely thank my advisor Roland N. Horne for always tactfully providing direction throughout my research, for inspiring and embracing unique solutions in the laboratory, and for always staying late to engage in worldy affairs on Friday afternoons. My great thanks go out to Kewen Li for his guidance and insight in the laboratory. Then last but not least, the Geothermal group, Egill, Aysegul, Chumei, Nick, Allen, Anson, and Laura, thank you for your support, humor, and helping hand throughout all the research