Thesis (MTech (Electrical Engineering))--Cape Peninsula University of Technology, 2016. / Tomography is the ability to internally visualise an opaque medium or a body, using different imaging techniques. Electrical Resistance Tomography (ERT) technique is a method commonly used in process tomography. It uses a non-intrusive resistance measurement between a set of electrodes attached on the circumference of a fixed cross-section with a given conductivity and permittivity distribution. ERT appears to be simple, low cost, safe and non-invasive. Despite the advantages of ERT, the reconstruction of the internal conductivity of the pipe still face a crucial challenges such as noise, a relatively low spatial resolution, as well as ill-posedness of the inverse problem when doing the image reconstruction using reconstruction algorithms. Although previous work showed the potential of various algorithms for the reconstruction of ERT tomograms, no full characterisation and comparison of different algorithms could be found for real flow situations. The ERT system was tested in the identification of different objects and fluid beds in a real time situation. The data collected from the measurements were then used for the image reconstruction using an algorithm developed by Time Long (One-step algorithm) and four EIDORS-based algorithms namely: Gauss-Newton algorithm with Laplace Prior (LP) and Gaussian prior (Automatic Hyper Parameter Selection (AHSP)), the Total Variation (TV) algorithm and the Conjugate Gradient (CG) algorithm. The performance of each algorithm was tested in different scenarios. The results obtained were then compared based on the quality and the accuracy of the images as well as the computational time of each algorithm. Firstly, reconstructed images were obtained using objects placed inside the ERT pipe test. Secondly, the algorithm performances were put to test in a level bed setup experiment and finally, the algorithm reconstructions were applied to the real flow situation, where different flow rates were applied. The results obtained were then analysed and compared.

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.

Within neurophysiology, there is need for improvements to functional brain imaging devices. Neural processing within the brain occurs on milli-second through to second timescales. Currently there are no systems with the sufficient temporal resolution and depth sensitivity. Electrical impedance tomography (EIT) is a technique that offers milli-second imaging, depth sensitivity, portability and low cost. It is already applied routinely in other medical applications such as lung function monitoring and breast imaging. The research presented in this thesis has contributed to the design and development of a 32-electrode EIT system, known as fEITER (functional Electrical Impedance Tomography of Evoked Responses). fEITER has been designed to be a brain imaging device that has a temporal resolution of 100 fps with an overall SNR of greater than 70 dB operating at 10 kHz. In order to carry out human tests using fEITER, the system required applications to the local and national ethics (NRES) as well as safety standards regulation (MHRA). These processes were successfully completed, receiving a 'notice of no objection' for a clinical trial using fEITER at The University of Manchester and Manchester Royal Infirmary. A series of tank tests were analysed as a method of understanding the system performance. The data obtained from human tests showed unique results. The reference data showed a repeating 'saw tooth' that is time-locked to the heart beat of the volunteer, which is a novel observation in medical EIT. Furthermore, the auditory stimuli data showed topographical differences across the scalp with respect to the startle and controlled auditory stimuli. These observations are based on single-event evoked responses, which is unique within the field of evoked potential studies. From the observations reported in this thesis it is plausible that fEITER is measuring voltages changes that are due to the neural processing.

EIT is a method of imaging that exists for a century, initially in geophysics and in recent years in medical imaging. Even though the practical applications of EIT go back to the early 20th century the systematic study of the inverse conductivity problem started in the late 1970s, hence many aspects of the problem remain unexplored. In the study of the inverse conductivity problem usually Finite Element Models are used since they can be easily adapted for bodies of irregular shapes. In this work though we use an equivalent approximation, the electrical resistor network, for which many uniqueness results as well as reconstruction algorithms exist. Furthermore resistor networks are important for EIT since they are used to provide convenient stable test loads or phantoms for EIT systems. In this thesis we study the transfer resistance matrix of a resistor network that is derived from n-port theory and review necessary and sufficient conditions for a matrix to be the transfer resistance of a planar network. The so called “paramountcy” condition may be useful for validation purposes since it provides the means to locate problematic electrodes. In the study of resistor networks in relation to inverse problems it is of a great importance to know which resistor networks correspond to some Finite Element Model. To give a partial answer to this we use the dual graph of a resistor network and we represent the voltage by the logarithm of the circle radius. This representation in combination with Duffin’s non-linear resistor network theory provides the means to show that a non-linear resistor network can be embedded uniquely in a Euclidean space under certain conditions. This is where the novelty of this work lies.

We present a novel two-dimensional (2D) MAET scanner, with a rotating object of interest and two fixed pairs of electrodes. Such an acquisition scheme, with our novel reconstruction techniques, recovers the boundaries of the regions of constant conductivity uniformly well, regardless of their orientation. We also present a general image reconstruction algorithm for the 2D MAET in a circular chamber with point-like electrodes immersed into the saline surrounding the object. An alternative linearized reconstruction procedure is developed, suitable for recovering the material interfaces (boundaries) when a non-ideal piezoelectric transducer is used for acoustic excitation. The work of the scanner and the linearized reconstruction algorithm is demonstrated using several phantoms made of high-contrast materials and a biological sample.

Atualmente existem diversos métodos e equipamentos disponíveis no mercado para análise da biomecânica do movimento humano. No entanto, mesmo uma equipe multidisciplinar, dispondo de um laboratório completo de análise do movimento, pode falhar na identificação de quais grupos musculares estão sendo recrutados durante um exercício. Sobretudo quando a musculatura de interesse é profunda. O objetivo desta tese é propor formas de detectar a contração muscular através da Tomografia por Impedância Elétrica (TIE). Um modelo de elementos finitos de condução elétrica é utilizado para resolver o problema inverso através do algoritmo de Newton-Raphson de forma a obter as imagens de TIE. Um novo modelo de eletrodo e o método de erro de discretização da malha são introduzidos como forma de melhorar as imagens de TIE. Além disso, a variabilidade da impeditividade de tecidos musculo-esqueléticos é medida experimentalmente, in vivo tanto em repouso quanto em exercício. Os resultados mostram que o sangue tem um papel importante nas mudanças de impeditividade e que as variações medidas durante as contrações musculares parecem estar relacionadas à taxa de contração do movimento. As imagens de TIE, obtidas in vivo de um voluntário, apresentam um aumento de resistividade durante a contração muscular. / Presently, there are several methods and equipment available in the market for the biomechanical analysis of human movement. However, even a well trained multidisciplinary team, equipped with a complete motion analysis laboratory, may fail to identify which muscle groups are being recruited during an exercise. Specially when deep muscles are being considered. The main objective of this work is to propose forms to detect muscle contraction from Electrical Impedance Tomography (EIT) images. A finite element electrical conduction model is used to solve an inverse problem with Newton-Raphson algorithm in order to produce EIT images. A new electrode model is proposed and the mesh discretization error method is implemented to improve EIT images. Additionally the variability of impeditivity of musculo-skeletal tissues is measured experimentally in vivo both at rest and during exercise. The results show that blood has an important role in muscle impeditivity changes and that resistivity variations during muscle contractions seem to be related to movement contraction rate. The EIT images, obtained in vivo from a volunteer, show an increase of resistivity during muscle contraction.

A Tomografia por Impedância Elétrica (TIE) aplica-se no monitoramento contínuo e detecção de alterações pulmonares sérias. Principalmente no ambiente das unidades de terapia intensiva (UTI) para a avaliação das condições do paciente em estado crítico submetido à ventilação artificial sem que seja necessário retirar o paciente da UTI e dos diferentes instrumentos de assistência à vida. A técnica permite estimar alterações de impedância nos pulmões. O objetivo deste trabalho é diminuir o erro numérico num algoritmo desenvolvido para TIE, utilizando o Filtro Estendido de Kalman. Especificamente, esse algoritmo aplica-se na a obtenção de imagens dos pulmões do corpo humano. Para realizar tal objetivo foram projetados phantoms compostos por um recipiente circular com solução salina, dentro do qual é colado um objeto cilíndrico de vidro e 32 eletrodos localizados no contorno do recipiente. Foi desenvolvido um algoritmo em linguagem C, utilizando a técnica de Filtro Estendido de Kalman para estimação de parâmetros de um modelo de elementos finitos. Foram implementados o procedimento de renumeração da malha de elementos finitos, com o objetivo de obter uma matriz de condutividade de banda, e o procedimento de melhoramento iterativo da solução para diminuir o erro numérico de soluções de sistemas lineares. Foram comparados dois algoritmos, um utilizando matriz de condutividade esparsa Alg Esparsa e outro com matriz de condutividade de banda limitada, obtida por renumeração da malha, e aplicando refinamento iterativo na solução de sistemas lineares, Alg RRI. Obtiveram-se melhores estimativas de impedância e uma melhor estabilidade do algoritmo do Filtro de Kalman com o algoritmo Alg RRI. O erro numérico na inversa da matriz de condutividade e o erro numérico na matriz de sensibilidade são significativamente menores quando se utiliza renumeração da malha e refinamento iterativo da solução de sistemas lineares. A redução de erro numérico nestas matrizes leva a melhores imagens. / The Electrical Impedance Tomography (EIT) is applied for the continuing monitoring and detection of serious pulmonar change. It may be used in intensive care units for the evaluation of patient condition in critical state submitted to artificial ventilation. It is not necessary to leave the intensive care unit and disconnect life assist devices. This technique allow estimation of impedance distribution on a cross section of the thorax. The main of this work is the reduction of numerical error in the Kalman Filter for EIT image estimation. Specifically, this algorithm may be applied for estimating lunge impedance distribution. To obtain this objective a phantom was developed. It is constituted by a cilindrical container with saline solution, a glass object is glued to the container, and 32 electrodes attached to the container wall. An algorithm in C language, using the Extended Kalman Filter technique was developed, it is a parameter estimation procedure. Mesh renumbering, to obtain a band limited conductivity matrix and the iterative improvement of the solution of linear systems were implemented. The estimation of impedance distribution was performed. Two different algorithms were considered. One algorithm uses a sparse conductivity matrix, Alg sparse. Another algorithm uses a band limited conductivity matrix and iterative refinement of the solution of linear systems, Alg RRI. Better impedance estimation and better stability of Kalman Filter algorithm was obtained using Alg RRI. The numerical error on the inverse of the conductivity matrix and the numerical error on the sensitivity matrix were smaller on algorithm Alg RRI. The numerical error reduction on the conductivity matrix and on the sensitivity matrix produced better images.

Este trabalho estuda a técnica de reconstrução de imagens conhecido como tomografia por impedância elétrica em um domínio bidimensional. Esta técnica consiste na alocação de eletrodos na fronteira do volume e uma fonte injeta padrões de corrente através dos eletrodos e medem-se as voltagens resultantes na fronteira. Com estes dados estima-se a condutividade (ou resistividade) do interior do domínio criando-se uma imagem do mesmo. A tomografia por impedância elétrica é um problema inverso e mal posto no sentido de Hadamard. Estudam-se diversos métodos de solução para resolver o problema direto usando métodos numéricos como diferenças finitas e volumes finitos. Proporemos os métodos numéricos a serem aplicados na solução do problema direto os quais serão testados com problemas onde a solução analítica é conhecida. Posteriormente aplicaremos os métodos propostos ao problema especifico. Uma questão importante na reconstrução de imagens é propor a maneira como aproximar o Jacobiano (ou matriz de sensibilidade) do problema, assim desenvolvemos uma técnica para a aproximação do mesmo usando os dados fornecidos pelo problema direto. / In this work is studied the technique of reconstruction of images known as electrical impedance tomography for a two-dimensional domain. This technique consists in the allocation of electrodes on the border of the volume and a source injects patterns of current through the electrodes and then measuring voltages through the other electrodes. With these data it is estimated the conductivity (or resistivity) on the interior of the domain and an image is create of it. The electrical impedance tomography is an inverse and ill conditioned problem in the Hadamard sense. In this work, is studying some numerical methods to solve the direct problem and are applied numerical methods such as the finite difference method and the finite volume method. It is proposed some numerical methods to solve the direct problem which will be tested with analytical problems where the solution is known. Later, apply the methods proposed to the specific issue. An important issue in the reconstruction problems is about the Jacobian (or sensitivity matrix) aproximation, thus proposing a technique for the calculation of even using the data provided by the direct problem. Keywords:

A Tomografia por Impedância Elétrica (TIE) aplica-se no monitoramento contínuo e detecção de alterações pulmonares sérias. Principalmente no ambiente das unidades de terapia intensiva (UTI) para a avaliação das condições do paciente em estado crítico submetido à ventilação artificial sem que seja necessário retirar o paciente da UTI e dos diferentes instrumentos de assistência à vida. A técnica permite estimar alterações de impedância nos pulmões. O objetivo deste trabalho é diminuir o erro numérico num algoritmo desenvolvido para TIE, utilizando o Filtro Estendido de Kalman. Especificamente, esse algoritmo aplica-se na a obtenção de imagens dos pulmões do corpo humano. Para realizar tal objetivo foram projetados phantoms compostos por um recipiente circular com solução salina, dentro do qual é colado um objeto cilíndrico de vidro e 32 eletrodos localizados no contorno do recipiente. Foi desenvolvido um algoritmo em linguagem C, utilizando a técnica de Filtro Estendido de Kalman para estimação de parâmetros de um modelo de elementos finitos. Foram implementados o procedimento de renumeração da malha de elementos finitos, com o objetivo de obter uma matriz de condutividade de banda, e o procedimento de melhoramento iterativo da solução para diminuir o erro numérico de soluções de sistemas lineares. Foram comparados dois algoritmos, um utilizando matriz de condutividade esparsa Alg Esparsa e outro com matriz de condutividade de banda limitada, obtida por renumeração da malha, e aplicando refinamento iterativo na solução de sistemas lineares, Alg RRI. Obtiveram-se melhores estimativas de impedância e uma melhor estabilidade do algoritmo do Filtro de Kalman com o algoritmo Alg RRI. O erro numérico na inversa da matriz de condutividade e o erro numérico na matriz de sensibilidade são significativamente menores quando se utiliza renumeração da malha e refinamento iterativo da solução de sistemas lineares. A redução de erro numérico nestas matrizes leva a melhores imagens. / The Electrical Impedance Tomography (EIT) is applied for the continuing monitoring and detection of serious pulmonar change. It may be used in intensive care units for the evaluation of patient condition in critical state submitted to artificial ventilation. It is not necessary to leave the intensive care unit and disconnect life assist devices. This technique allow estimation of impedance distribution on a cross section of the thorax. The main of this work is the reduction of numerical error in the Kalman Filter for EIT image estimation. Specifically, this algorithm may be applied for estimating lunge impedance distribution. To obtain this objective a phantom was developed. It is constituted by a cilindrical container with saline solution, a glass object is glued to the container, and 32 electrodes attached to the container wall. An algorithm in C language, using the Extended Kalman Filter technique was developed, it is a parameter estimation procedure. Mesh renumbering, to obtain a band limited conductivity matrix and the iterative improvement of the solution of linear systems were implemented. The estimation of impedance distribution was performed. Two different algorithms were considered. One algorithm uses a sparse conductivity matrix, Alg sparse. Another algorithm uses a band limited conductivity matrix and iterative refinement of the solution of linear systems, Alg RRI. Better impedance estimation and better stability of Kalman Filter algorithm was obtained using Alg RRI. The numerical error on the inverse of the conductivity matrix and the numerical error on the sensitivity matrix were smaller on algorithm Alg RRI. The numerical error reduction on the conductivity matrix and on the sensitivity matrix produced better images.

Abstract not available