EIT Reconstruction Algorithms: Pitfalls, Challenges and Recent Developments

We review developments, issues and challenges in Electrical Impedance Tomography (EIT), for the 4th Workshop on Biomedical Applications of EIT, Manchester 2003. We focus on the necessity for three dimensional data collection and reconstruction, efficient solution of the forward problem and present and future reconstruction algorithms. We also suggest common pitfalls or ``inverse crimes'' to avoid.Comment: A review paper for the 4th Workshop on Biomedical Applications of EIT, Manchester, UK, 200

Electrical Impedance Tomography: From the Traditional Design to the Novel Frontier of Wearables

Electrical impedance tomography (EIT) is a medical imaging technique based on the injection of a current or voltage pattern through electrodes on the skin of the patient, and on the reconstruction of the internal conductivity distribution from the voltages collected by the electrodes. Compared to other imaging techniques, EIT shows significant advantages: it does not use ionizing radiation, is non-invasive and is characterized by high temporal resolution. Moreover, its low cost and high portability make it suitable for real-time, bedside monitoring. However, EIT is also characterized by some technical limitations that cause poor spatial resolution. The possibility to design wearable devices based on EIT has recently given a boost to this technology. In this paper we reviewed EIT physical principles, hardware design and major clinical applications, from the classical to a wearable setup. A wireless and wearable EIT system seems a promising frontier of this technology, as it can both facilitate making clinical measurements and open novel scenarios to EIT systems, such as home monitoring

Active complex electrode (ACE1) electrical impedance tomography system & anatomically inspired modeling of electrode-skin contact impedance, The

Includes bibliographical references.2016 Summer.Electrical Impedance Tomography (EIT) is a technique used to image the varying electrical properties of biological tissues or tissue conductivity and permittivity. There are many clinical uses of EIT, but as a newer imaging modality, there is interest in improving hardware to acquire EIT data, creating models of the system and generating high quality images. The two main contributions of this work include: (1) EIT hardware advancements and (2) software modeling to simulate measured human subject data. Specifically, this dissertation includes the design and testing of Colorado State University's first EIT system, the pairwise current injection active complex electrode (ACE1) system for phasic voltage measurement. The ACE1 system was primarily designed for thoracic EIT applications, and its performance and limitations were tested through a variety of experiments. Additionally, the EIT forward problem was used to investigate electrode-skin contact impedance

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 bioimpedance-based monitor for real-time detection and identification of secondary brain injury

Secondary brain injury impacts patient prognosis and can lead to long-term morbidity and mortality in cases of trauma. Continuous monitoring of secondary injury in acute clinical settings is primarily limited to intracranial pressure (ICP); however, ICP is unable to identify essential underlying etiologies of injury needed to guide treatment (e.g. immediate surgical intervention vs medical management). Here we show that a novel intracranial bioimpedance monitor (BIM) can detect onset of secondary injury, differentiate focal (e.g. hemorrhage) from global (e.g. edema) events, identify underlying etiology and provide localization of an intracranial mass effect. We found in an in vivo porcine model that the BIM detected changes in intracranial volume down to 0.38 mL, differentiated high impedance (e.g. ischemic) from low impedance (e.g. hemorrhagic) injuries (p \u3c 0.001), separated focal from global events (p \u3c 0.001) and provided coarse ‘imaging’ through localization of the mass effect. This work presents for the first time the full design, development, characterization and successful implementation of an intracranial bioimpedance monitor. This BIM technology could be further translated to clinical pathologies including but not limited to traumatic brain injury, intracerebral hemorrhage, stroke, hydrocephalus and post-surgical monitoring

A portable EIT system for emergency medical care

Electrical Impedance Tomography (EIT) is a medical imaging technique in which images of tissue conductivity within a body can be inferred from surface electrode measurements. The main goal of this study is to develop a portable EIT system incorporating an optimized electrode layout to detect intracranial haematomas for use in emergency care. A growing haematoma can cause severe and even permanent damage to the delicate tissue of the brain, morbidity, and eventual death of the patient. No capability is at present available for the diagnosis of haematomas pre-hospitalisation or by first-responders. The lack of this crucial information can lead to bad decisions on patient management, and in particular, where to send the patient. Blood has a high electrical conductivity contrast relative to other cranial tissue and can be detected and monitored using electrical impedance methods. EIT is a non-invasive, low-cost monitoring alternative to other imaging modalities, and has the potential to detect bleeding and to localize the approximate bleeding site. A device of this nature would reduce treatment delays, save on costs and waste, and most significantly, positively impact patient outcomes. The first step was a numerical simulation study on FE models. The full array and the hemi-array electrode layouts were modelled and the anomalies were simulated in different positions with different sizes. The results were obtained using TSVD and WMNM reconstruction methods by COMSOL linked with MATLAB. The simulated anomalies were detected for all the positions using both layouts; however those from the full array were in general superior to the hemi-array. In order to perform realistic experiments, a prototype EIT system was constructed in the laboratory. The constructed EIT has 16 channels and operates in the frequency range of 10 kHz to 100 kHz with a temporal resolution of 100 frames per second and high level of accuracy of 93.5 %. The minimum number of 8 electrodes was chosen in this study for emergency care. Minimizing the number of electrodes speeds up the electrode setup process and avoids the need to move the patient s head in emergency care. In the second part of this study, phantom experiments were performed to find an optimised electrode layout for emergency care. The full array and the hemi-array were investigated using phantom experiments. As expected, the full array layout had the best performance in general; however, the performance of the hemi-array layout was very poor. Thus a novel optimised electrode layout (semi-array) for emergency care was proposed and evaluated in phantom experiments. For the hemi-array and the semi-array layouts, measurement sensitivity depends strongly on the anomaly location since the electrodes are not placed all over the head. The HA layout performed very badly, with the best radial localization error of 0.8100 mm, compared to the SA layout with the worst error of 0.2486 mm. Some reconstructed anomalies located far from the electrodes in the posterior region were almost invisible or erroneous for the hemi-array layout; however, it is enhanced by using the semi-array layout. Finally, in vitro experiments were conducted on ovine models. In most of the experiments carried out by other researchers, since the location of the simulated anomalies was not known and the simulated blood was normally injected into the body or the head, localization of the anomalies was not considered and the quantity of the injected blood was investigated solely. In our new method of experiment, the position of the anomalies was known a priori and thus could be compared accurately to the EIT results. The full array and the semi-array layouts were compared in terms of detection, localisation and size estimation of haematomas. As expected, the full array layout was found to be more robust than the semi-array layout with the best mean value of the localization error of 0.0564 mm and the worst QI error of around 30%. Using a minimum number of electrodes in an optimised layout is always desirable in clinical applications. The semi-array 8-electrode layout prevents unnecessary movements and the electrode connections to the head would be very quick in emergency care. Although the semi-array 8-electrode layout reduced the sensitivity of the measurements, the findings from the experiments indicated its potential to detect and monitor haematomas and probably extend its application for emergency applications where the required accuracy is not critical

The ACE1 Electrical Impedance Tomography System for Thoracic Imaging

The design and performance of the active complex electrode (ACE1) electrical impedance tomography system for single-ended phasic voltage measurements are presented. The design of the hardware and calibration procedures allows for reconstruction of conductivity and permittivity images. Phase measurement is achieved with the ACE1 active electrode circuit which measures the amplitude and phase of the voltage and the applied current at the location at which current is injected into the body. An evaluation of the system performance under typical operating conditions includes details of demodulation and calibration and an in-depth look at insightful metrics, such as signal-to-noise ratio variations during a single current pattern. Static and dynamic images of conductivity and permittivity are presented from ACE1 data collected on tank phantoms and human subjects to illustrate the system\u27s utility

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