Towards a Universal Methodology for Performance Evaluation of Electrical Impedance Tomography Systems using Full Reference SNR

This paper describes a simple and reproducible methodology towards a universal figure-of-merit (FoM) for evaluating the performance of electrical impedance tomography (EIT) systems using reconstructed images. Based on objective full-referencing and signal-to-noise ratio, the method provides a visually distinguishable hot-map and two new FoM factors, to address the issues where common electrical parameters are not directly related to the quality of EIT images. The paper describes the method with simulation results and develops a 16 electrode EIT system using an ASIC front-end for evaluation using the proposed method. The measured results show both visually and in terms of the proposed FoM factors, the impact on recorded EIT images with different current injection amplitudes

Very Low Frequency Electrical Impedance Tomography Image Reconstruction System Using FPGA Software-Hardware Co-design

Electrical Impedance Tomography (EIT) is an imaging technique which is noninvasive and uses the internal conductivity distribution of the object of interest to form a tomographic image. It is performed by applying electrodes to the surface of the object. An alternating current up to frequency 10kHz is applied through a pair of electrodes, and the induced voltage is measured on other electrodes. These current and voltage values are used to reconstruct the internal conductivity distribution. The EIT imaging is increasingly getting used in clinical applications, as it is safer, portable, and low cost if compared with available imaging technologies used in clinical settings. The goal of this project is to develop a low frequency Zynq SoC-based EIT system. A Zynq 7020 device-based development board, Zedboard, interfaced with a customized hardware circuit, is used to develop a complete EIT system. A graphical user interface is developed using C# Graphic User Interface (GUI) application to control the hardware and visualize the results. It is a twelve-electrode system, and current injection and voltage measurement is performed through Zynq SoC. There are two image reconstruction algorithms developed, Gauss Newton One Step and Total variation. The algorithms are implemented in Zynq SoC using software-hardware co-design. The algorithms are also implemented in C#. The image reconstruction performance between the two algorithms is compared. The computation performance between Zynq SoC implementation and C# implementation is also compared to understand the feasibility of FPGA implementation of EIT image reconstruction algorithms

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

Electrical Impedance Tomography (EIT): The Establishment of a Dual Current Stimulation EIT System for Improved Image Quality

Electrical Impedance Tomography (EIT) is a noninvasive imaging technique that reproduces images of cross-sections, based on the internal impedance distribution of an object. This Dissertation investigates and confirms the use of a dual current stimulation EIT (DCS EIT) system. The results of this investigation presented a size error of 2.82 % and a position error of 5.93 % in the reconstructed images, when compared to the actual size and position of the anomaly inside a test object. These results confirmed that the DCS EIT system produced images of superior quality (fewer image reconstruction errors) to those produced from reviewed single plane stimulating EIT systems, which confirmed the research hypothesis. This system incorporates two independent current stimulating patterns, which establishes a more even distribution of current in the test object, compared to single plane systems, and is more efficient than 2.5D EIT systems because the DCS EIT system only measures boundary voltages in the center plane, compared to 2.5D EIT systems that measure the boundary voltages in all electrode planes. The system uses 48 compound electrodes, divided into three electrode planes. Current is sourced and sunk perpendicularly in the center plane, to produce a high current density near the center of the test object. Sequentially, current is sourced through an electrode in the top electrode plane and sunk through an electrode in the bottom plane, directly below the source electrode, to produce a high current density near the boundary of the test object, in the center plane. During both injection cycles, boundary potentials are measured in the center plane. Following the measurement of a complete frame, a weighted average is computed from the single and cross plane measured data. The weighted measured voltages, injected currents and Finite Element Model of the object is used to reconstruct an image of the internal impedance distribution along a cross-section of the object. This method is applicable to the biomedical imaging and process monitoring fields

A Wideband Contactless Electrical Impedance Tomography System

This work focuses on the development of a wideband contactless electrical impedance tomography (EIT) system. The system is developed from the aspects of the multifrequency capacitively coupled electrical impedance tomography (CCEIT) hardware, the impedance calculation model and the system evaluation. The hardware includes a 12-electrode CCEIT sensor, 6 sensing modules, a data acquisition module, and a personal computer (PC). The impedance calculation model is established by combining the mechanism modeling of the integrated circuits (ICs) and the empirical modeling of the measurement data with the least squares (LS) method. Experiments were carried out to evaluate the developed system, including the signal-to-noise ratio (SNR), the impedance measurement accuracy and the imaging performance. Experimental results show that the system achieves an SNR above 65.00 dB for the frequencies up to 20 MHz. Impedance measurement results indicate that the system has good impedance measurement accuracy at frequencies below 10 MHz and acceptable impedance measurement accuracy at 10 MHz - 20 MHz. It has particularly good performance at several specific frequencies, which can also serve as a high-performance single-frequency contactless EIT device. Imaging results show that the spectroscopic images reconstructed by the developed system are consistent with the actual distributions. Few types of research on contactless multifrequency EIT systems have been reported. So, this work is of great significance for further development and practical application of the newly emerged contactless EIT technique

Tomografía de impedancia eléctrica: fundamentos de hardware y aplicaciones médicas

Introduction: The following article shows a systematic review of publications on hardware topologies used to capture and process electrical signals used in Electrical Impedance Tomography (EIT) in medical applications, as well topicality of the EIT in the field of biomedicine. This work is the product of the research project “Electrical impedance tomography based on mixed signal devices”, which took place at the University of Cauca during the period 2017-2019. Objective: This review describes the operation, topicality and clinical use of Electrical Impedance Tomography systems. Methodology: A systematic review was carried out in the IEEE-Xplore, ScienceDirect and Scopus databases. After the classification, 106 relevant articles were obtained on scientific studies of EIT systems; applications dedicated to the analysis of medical images. Conclusions: Impedance-based methods have a variety of medical applications as they allow for the reconstruction of a body region, by estimating the conductivity distribution inside the human body; this is without exposing the patient to the damaging effects of radiation and contrast elements. Impedance-based methods are therefore a very useful and versatile tool in the treatment of diseases such as: monitoring blood pressure, detection of atherosclerosis, localization of intracranial hemorrhages, determining bone density, among others. Originality: It describes the necessary components to design an EIT system, as well as the design characteristics depending on the pathology to be visualized.  Introducción: En el siguiente artículo se muestra una revisión sistemática de publicaciones sobre topologías hardware utilizadas para capturar y procesar señales eléctricas utilizadas en tomografía por impedancia eléctrica (TIE) en aplicaciones médicas, así como la actualidad del TIE en el campo de la biomedicina. Este trabajo es producto del proyecto de investigación “Tomografía de impedancia eléctrica basada en dispositivo de señal mixta”, que tiene lugar en la Universidad del Cauca durante el período 2017-2019.   Objetivo: Esta revisión describe la estructura hardware de los sistemas de TIE, además de sus características, como frecuencia y magnitud de señales de corriente, patrones de inyección y medición de señales y número de electrodos orientado a, uso clínico.   Metodología: Se realizó una revisión sistemática, en las bases de datos IEEE-Xplore, ScienceDirect y Scopus. Tras la clasificación se obtuvo 106 artículos relevantes sobre estudios científicos de sistemas, aplicaciones dedicadas al análisis de imágenes médicas.   Conclusión: Los métodos basados en impedancia, tienen una variedad de aplicaciones médicas, puesto que permite la reconstrucción de una región corporal, mediante la estimación de la distribución de conductividad al interior del cuerpo humano, sin radiación y elementos de contraste, tan perjudiciales para la salud de los pacientes; convirtiéndola en una herramienta muy útil y versátil en el tratamiento de enfermedades como: monitorear la presión arterial, detección de arterosclerosis, localización de hemorragias intracraneales, determinar la densidad ósea, entre otras.     &nbsp

A high frame rate wearable EIT system using active electrode ASICs for lung respiration and heart rate monitoring

A high specification, wearable, electrical impedance tomography (EIT) system with 32 active electrodes is presented. Each electrode has an application specific integrated circuit (ASIC) mounted on a flexible printed circuit board, which is then wrapped inside a disposable fabric cover containing silver-coated electrodes to form the wearable belt. It is connected to a central hub that operates all the 32 ASICs. Each ASIC comprises a high- performance current driver capable of up to 6 mAp−p output, a voltage buffer for EIT and heart rate signal recording as well as contact impedance monitoring, and a sensor buffer that provides multi-parameter sensing. The ASIC was designed in a CMOS 0.35-μm high-voltage process technology. It operates from ±9-V power supplies and occupies a total die area of 3.9 mm2. The EIT system has a bandwidth of 500 kHz and employs two parallel data acquisition channels to achieve a frame rate of 107 frames/s, the fastest wearable EIT system reported to date. Measured results show that the system has a measurement accuracy of 98.88% and a minimum EIT detectability of 0.86 Q/frame. Its successful operation in capturing EIT lung respiration and heart rate biosignals from a volunteer is demonstrated

A high frame rate wearable EIT system using active electrode ASICs for lung respiration and heart rate monitoring

A high specification, wearable, electrical impedance tomography (EIT) system with 32 active electrodes is presented. Each electrode has an application specific integrated circuit (ASIC) mounted on a flexible printed circuit board, which is then wrapped inside a disposable fabric cover containing silver-coated electrodes to form the wearable belt. It is connected to a central hub that operates all the 32 ASICs. Each ASIC comprises a high- performance current driver capable of up to 6 mAp−p output, a voltage buffer for EIT and heart rate signal recording as well as contact impedance monitoring, and a sensor buffer that provides multi-parameter sensing. The ASIC was designed in a CMOS 0.35-μm high-voltage process technology. It operates from ±9-V power supplies and occupies a total die area of 3.9 mm2. The EIT system has a bandwidth of 500 kHz and employs two parallel data acquisition channels to achieve a frame rate of 107 frames/s, the fastest wearable EIT system reported to date. Measured results show that the system has a measurement accuracy of 98.88% and a minimum EIT detectability of 0.86 Q/frame. Its successful operation in capturing EIT lung respiration and heart rate biosignals from a volunteer is demonstrated