817 research outputs found

    Frequency-Division Multiplexing for Electrical Impedance Tomography in Biomedical Applications

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    Electrical impedance tomography (EIT) produces an image of the electrical impedance distribution of tissues in the body, using electrodes that are placed on the periphery of the imaged area. These electrodes inject currents and measure voltages and from these data, the impedance can be computed. Traditional EIT systems usually inject current patterns in a serial manner which means that the impedance is computed from data collected at slightly different times. It is usually also a time-consuming process. In this paper, we propose a method for collecting data concurrently from all of the current patterns in biomedical applications of EIT. This is achieved by injecting current through all of the current injecting electrodes simultaneously, and measuring all of the resulting voltages at once. The signals from various current injecting electrodes are separated by injecting different frequencies through each electrode. This is called frequency-division multiplexing (FDM). At the voltage measurement electrodes, the voltage related to each current injecting electrode is isolated by using Fourier decomposition. In biomedical applications, using different frequencies has important implications due to dispersions as the tissue's electrical properties change with frequency. Another significant issue arises when we are recording data in a dynamic environment where the properties change very fast. This method allows simultaneous measurements of all the current patterns, which may be important in applications where the tissue changes occur in the same time scale as the measurement. We discuss the FDM EIT method from the biomedical point of view and show results obtained with a simple experimental system

    Electrical Impedance Tomography/Spectroscopy (EITS): a Code Division Multiplexed (CDM) approach

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    Electrical Impedance Tomography and Spectroscopy (EITS) is a noninvasive imaging technique that creates images of cross-sections "tomos" of objects by discriminating them based on their electrical impedance. This thesis investigated and successfully confirmed the use of Code Division Multiplexing (CDM) using Gold codes in Electrical Impedance Tomography and Spectroscopy. The results obtained showed 3.5% and 6.2% errors in determining the position and size of imaged anomalies respectively, with attainable imaging speed of 462 frames/second. These results are better, compared to those reported when using Time Division Multiplexing (TDM) and Frequency Division Multiplexing (FDM).This new approach provides a more robust mode of EITS for fast changing dynamic systems by eliminating temporal data inconsistencies. Furthermore, it enables robust use of frequency difference imaging and spectroscopy in EITS by eliminating frequency data inconsistencies. In this method of imaging, electric current patterns are safely injected into the imaged object by a set of electrodes arranged in a single plane on the objects surface, for 2-Dimensional (2D) imaging. For 3-Dimensional (3D) imaging, more electrode planes are used on the objects surface. The injected currents result in measurable voltages on the objects surface. Such voltages are measured, and together with the input currents, and a Finite Element Model (FEM) of the object, used to reconstruct an impedance image of the cross-sectional contents of the imaged object. The reconstruction process involves the numerical solutions of the forward problem; using Finite Element solvers and the resulting ill-posed inverse problem using iterative Optimization or Computational Intelligence methods. This method has applications mainly in the Biomedical imaging and Process monitoring fields. The primary interests of the author are, in imaging and diagnosis of cancer, neonatal pneumonia and neurological disorders which are leading causes of death in Africa and world-wide

    Electrical Impedance Tomography for Biomedical Applications: Circuits and Systems Review

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    There has been considerable interest in electrical impedance tomography (EIT) to provide low-cost, radiation-free, real-time and wearable means for physiological status monitoring. To be competitive with other well-established imaging modalities, it is important to understand the requirements of the specific application and determine a suitable system design. This paper presents an overview of EIT circuits and systems including architectures, current drivers, analog front-end and demodulation circuits, with emphasis on integrated circuit implementations. Commonly used circuit topologies are detailed, and tradeoffs are discussed to aid in choosing an appropriate design based on the application and system priorities. The paper also describes a number of integrated EIT systems for biomedical applications, as well as discussing current challenges and possible future directions

    A New Concept for Medical Imaging Centered on Cellular Phone Technology

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    According to World Health Organization reports, some three quarters of the world population does not have access to medical imaging. In addition, in developing countries over 50% of medical equipment that is available is not being used because it is too sophisticated or in disrepair or because the health personnel are not trained to use it. The goal of this study is to introduce and demonstrate the feasibility of a new concept in medical imaging that is centered on cellular phone technology and which may provide a solution to medical imaging in underserved areas. The new system replaces the conventional stand-alone medical imaging device with a new medical imaging system made of two independent components connected through cellular phone technology. The independent units are: a) a data acquisition device (DAD) at a remote patient site that is simple, with limited controls and no image display capability and b) an advanced image reconstruction and hardware control multiserver unit at a central site. The cellular phone technology transmits unprocessed raw data from the patient site DAD and receives and displays the processed image from the central site. (This is different from conventional telemedicine where the image reconstruction and control is at the patient site and telecommunication is used to transmit processed images from the patient site). The primary goal of this study is to demonstrate that the cellular phone technology can function in the proposed mode. The feasibility of the concept is demonstrated using a new frequency division multiplexing electrical impedance tomography system, which we have developed for dynamic medical imaging, as the medical imaging modality. The system is used to image through a cellular phone a simulation of breast cancer tumors in a medical imaging diagnostic mode and to image minimally invasive tissue ablation with irreversible electroporation in a medical imaging interventional mode

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

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    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

    Shape sensing of variable stiffness soft robots using electrical impedance tomography

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    Soft robotic systems offer benefits over traditional rigid systems through reduced contact trauma with soft tissues and by enabling access through tortuous paths in minimally invasive surgery. However, the inherent deformability of soft robots places both a greater onus on accurate modelling of their shape, and greater challenges in realising intraoperative shape sensing. Herein we present a proprioceptive (self-sensing) soft actuator, with an electrically conductive working fluid. Electrical impedance measurements from up to six electrodes enabled tomographic reconstructions using Electrical Impedance Tomography (EIT). A new Frequency Division Multiplexed (FDM) EIT system was developed capable of measurements of 66 dB SNR with 20 ms temporal resolution. The concept was examined in two two-degree-of-freedom designs: a hydraulic hinged actuator and a pneumatic finger actuator with hydraulic beams. Both cases demonstrated that impedance measurements could be used to infer shape changes, and EIT images reconstructed during actuation showed distinct patterns with respect to each degree of freedom (DOF). Whilst there was some mechanical hysteresis observed, the repeatability of the measurements and resultant images was high. The results show the potential of FDM-EIT as a low-cost, low profile shape sensor in soft robots

    An Imaged-Based Method for Universal Performance Evaluation of Electrical Impedance Tomography Systems

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    This paper describes a simple and reproducible methodology for universal evaluation of the performance of electrical impedance tomography (EIT) systems using reconstructed images. Based on objective full referencing (FR), the method provides a visually distinguishable hot colormap and two new FR metrics, the global and the more specific region of interest, to address the issues where common electrical parameters are not directly related to the quality of EIT images. A passive 16 electrode EIT system using an application specific integrated circuit front-end was used to evaluate the proposed method. The measured results show, both visually and in terms of the proposed FR metrics, the impact on recorded EIT images with different design parameters and non-idealities. The paper also compares the image results of a passive electrode system with a matched single variable active electrode system and demonstrates the merit of an active electrode system for noise interference

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

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    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
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