Thesis (MScPhysio)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: Question: What are the effects of Intermittent Positive Pressure Breathing (with and without a Positive End Expiratory Pressure [PEEP] Valve), compared to deep breathing exercises, on ventilation distribution in high-risk adults following open upper abdominal surgery (UAS)? Design: This study comprised an observational descriptive component as well as a prospective triple blind randomised controlled crossover trial with concealed allocation and patient, assessor and statistician blinding Participants: Seven patients at high risk for postoperative pulmonary complications following UAS Intervention: Deep breathing exercises (DBExs) were compared to Intermittent Positive Pressure Breathing (IPPB), with IPPB further applied with and without a PEEP Valve, using a randomised cross-over design with 30 minute washout duration between periods. Outcome measures: Global and regional impedance changes in the lungs were measured using Electrical Impedance Tomography. Vital signs, visual analogue pain scale (VAS) and modified Borg scale (MBS) were measured pre– and post-intervention. Results: A greater mean global lung impedance change ( Z) was detected with IPPB compared to DBExs (mean difference in Z 2803.8; 95% CI 5189.9 to 8512.5 and 2046 to 96047.9; P<0.01). These changes in lung impedance lasted 30 minutes before returning to baseline. There was no difference in Z when patients received IPPB with 5cmH20 PEEP compared to IPPB with no PEEP. No specific regional ventilation changes were noted. IPPB did not increase VAS, MBS scores or adversely affect vital signs. Conclusion: IPPB is an effective technique to improve lung volumes compared to deep breathing exercises. Further studies are required to investigate the effect of IPPB on clinical outcome. / AFRIKAANSE OPSOMMING: Vraag: Watter uitwerking het onderbroke positiewe-drukasemhaling (met én sonder ’n positiewe-endekspiratoriesedruk-[PEEP-]klep) in vergelyking met diepasemhalings-oefeninge op ventilasieverspreiding by hoërisikovolwassenes ná bo-buikchirurgie? Ontwerp: ’n Waarnemingsgegronde, vergelykende en ondersoekende, driedubbelblinde, verewekansigde gekontroleerde oorskakelproef, met verborge toewysing en blinding van pasiënte, die assesseerder en statistikus Deelnemers: Sewe pasiënte met ’n hoë risiko vir post-operatiewe pulmonêre komplikasies na bo-buikchirurgie Intervensie: Diepasemhalingsoefeninge (DBEx) is vergelyk met onderbroke positiewedrukasemhaling (IPPB), wat op sy beurt met én sonder ’n PEEP-klep toegepas is, met behulp van ’n verewekansigde oorskakelstudie met ’n halfuur lange uitspoeling tussen oorskakelings. Uitkomsmetings: Algehele en regionale impedansieveranderinge in die longe is met behulp van elektriese impedansietomografie gemeet. Vitale tekens, die visuele analoogskaal (VAS) en die aangepaste Borg-skaal (MBS) is voor, sowel as na die intervensie afgeneem. Resultate: ’n Groter gemiddelde algehele impedansieverandering ( Z) is opgemerk met IPPB in vergelyking met DBEx (gemiddelde verskil 2803.8; 95% CI 5189.9: 8512.5 en 2046: 96047.9; P<0.01). Hierdie veranderinge in longimpedansie het ’n halfuur of langer geduur voordat dit na die basislyn teruggekeer het. Daar was geen verskil in Z toe pasiënte IPPB met ’n PEEP-klep van 5cmH20 ontvang het teenoor IPPB sonder ’n PEEP-klep nie. Geen spesifieke regionale voorkeure is opgemerk nie. IPPB het nie die VAS- of MBS-tellings verhoog of vitale tekens verswak nie. Stellenbosch University https://scholar.sun.ac.za iv Gevolgtrekking: In vergelyking met DBEx, is IPPB ’n doeltreffende tegniek om longvolumes te verbeter. Verdere studies word vereis om die uitwerking van IPPB op kliniese uitkomste te ondersoek.

A principal causa da disfunção respiratória em equinos durante anestesia geral inalatória é atribuída à hipoxemia devido a formação de áreas de atelectasias. Visando reverter estes quadros são instituídas as manobras de recrutamento alveolar (MRA) através da administração de elevadas pressões no sistema respiratório. Estas manobras quando utilizadas de maneira inadequada podem contribuir para a formação de atelectasias, barotrauma, volutrauma e até mesmo atelectrauma; sendo de suma importância a sua monitoração. Com isso, uma nova técnica, a tomografia por impedância elétrica (TIE), vem sendo estudada, no qual, seu funcionamento se dá por emissão de corrente elétrica de baixa frequência e intensidade nos tecidos, gerando uma imagem dos tecidos avaliados. Sendo assim, o objetivo do presente estudo experimental foi avaliar se na espécie equina a TIE é capaz de visualizar as alterações de volume corrente global e regional, em pulmões saudáveis, durante a ventilação mecânica e escalonamento da PEEP como MRA. Para tanto foram utilizados 14 equinos de peso médio de 306 kg, submetidos a anestesia geral inalatória em decúbito dorsal. Os animais foram mecanicamente ventilados com volume corrente de 14 mL/kg e frequência respiratória de 7-9 mpm. Foi instituída manobra de recrutamento alveolar, aumentando-se a PEEP de 5 em 5 cmH2O, a cada 5 minutos, até 32 cmH2O, seguido de seu decréscimo também de 5 em 5 cmH2O, a cada 5 minutos, até 7 cmH2O. Foram realizadas coletadas de amostras de sangue arterial para hemogasometria, imagens do TIE e registrados os parâmetros hemodinâmicos e de mecânica respiratória em cada estágio do escalonamento da PEEP. Durante a MRA foram observados aumento na PaO2/FiO2 dos pacientes assim como aumento na complacência estática pulmonar, associado a uma diminuição no shunt pulmonar, e deslocamento da ventilação para região pulmonar dependente por meio da TIE, principalmente em PEEP acima de 17 cmH2O. Como efeitos adversos foram observados alterações em parâmetros hemodinâmicos sendo estas transitórias. Portanto o TIE demonstrou-se capaz de avaliar as mudanças de ventilação pulmonar durante a MRA e mostrou relação com os ganhos em oxigenação e mecânica pulmonar. / The main cause of respiratory dysfunction in horses under isoflurane anaesthesia is hypoxemia attributed to the atelectasis formation areas. In order to revert these sets, alveolar recruitment manoeuvres (ARM) are instituted through high pressures administration in the respiratory system. These manoeuvres when used improperly can contribute to the atelectasis formation, barotrauma, volutrauma and even atelectrauma; being of utmost importance its monitoring. A new technique, electrical impedance tomography (EIT), has been studied, in which its operation is due to the low frequency and intensity of electric current emission in the tissues, generating tissues images for evaluation. Therefore, the present experimental study aimed to evaluate whether in horses the EIT is able to visualize changes of global and regional tidal volume in healthy lungs during mechanical ventilation and titration of PEEP as ARM. For this purpose, 14 horses weighting 306 kg were used, undergoing general inhalation anaesthesia in dorsal recumbence. The animals were mechanically ventilated with tidal volume of 14 mL/kg and respiration rate of 7-9 bpm. An alveolar recruitment manoeuvre was instituted, increasing the PEEP by 5 cmH2O every 5 minutes until 32 cmH2O, followed by decreasing it by 5 cmH2O every 5 minutes to 7 cmH2O. Arterial blood samples were collected for hemogasometry, EIT images and hemodynamic parameters and respiratory mechanics were recorded at each stage of PEEP. During ARM, patients\' PaO2/FiO2 increased as well as increased pulmonary static compliance, associated with a decrease in pulmonary shunt, and pulmonary ventilation moving to dependent areas, mainly when 17 cmH2O or more were applied. As adverse effects were observed transient changes in hemodynamic parameters. So TIE is capable of presenting the changes in pulmonary ventilation in horse in dorsal recumbency undergoing ARM, and showed good relation to oxygenation gain and respiratory mechanics.

Dans le cadre général des études de matériaux multifonctionnels, électrolytiques et catalytiques, susceptibles d’être utilisés au sein de dispositifs de détection de gaz, un système d’oxydes (1-x)CeO2. x/2Bi2O3 avec 0≤x≤1 a été élaboré par coprécipitation puis traitement thermique à 600°C. Le système ainsi obtenu correspondrait à un diagramme de phases original, constitué d’un domaine de solutions solides (Ce1-xBixO2-z pour x ≤ 0,20), d’un domaine multiphasé pour 0,3≤x≤0,7 comportant une phase de type quadratique b’-Bi2O3 et une phase cubique substituée limite (x=0,20), d’un autre domaine multiphasé pour les compositions 0,8≤x≤1, comportant une phase quadratique b-Bi2O3 et une phase monoclinique. Ces deux phases ont déjà été considérées dans la littérature comme phases métastables résultant de divers modes de refroidissement de la phase pure Bi2O3. Dans le cas présent, la stabilisation de ces deux phases b’ et b en présence d’une phase substituée cubique Ce1-xBixO2-z pourrait être due à la présence d’ions cérium au sein duréseau cristallin de Bi2O3. Les interactions catalytiques entre des échantillons polycristallins de ce système avec x variable et des mélanges air-CO et air CH4 ont été étudiées par spectroscopie infrarouge à transformée de Fourier dans le domaine 100 à 525°C. Il apparait que les composés riches en cérium ou riches en bismuth n'ont pas la même réactivité vis-à-vis des gaz CH4 ou CO. Cette diversité de propriétés catalytiques pourrait être utilisée au sein de systèmes multicapteurs de gaz.Une étude de la conduction électrique du système pour x variable a été effectuée par spectroscopie d’impédance électrique entre 100 et 750°C. Les représentations Nyquist des impédances électriques ont été interprétées en mettant en jeu des modèles de type élément de phase constante ou de type Warburg pour prendre en compte l’hétérogénéité des échantillons ainsi que les phénomènes de réaction-diffusion aux électrodes. La conductivité en volume (coeur de grains) augmente avec la composition, avec deux types d’évolutions distinctes : une évolution caractéristique de la phase substituée liée à l’augmentation du taux de lacunes, une évolution dans le système biphasé avec une forte augmentation de conductivité au-dessus de x=0,3 et un maximum atteint pour x=0,7. La phase quadratique de type b’-Bi2O3 connue comme phase métastable est ainsi stabilisée au sein de ce système mixte, au moins à 600°C: elle serait à l’origine de la forte conductivité ionique observée pour la composition proche de x = 0,7. / To develop multifunctional and sensitive materials for gas sensor, catalytic microsystems and electrolytic applications, the multiphase system (1-x).CeO2 + ½ x.Bi2O3 has been investigated in the bismuth composition range 0≤x≤1. A series of ceramics samples has been prepared via a coprecipitation route followed by a thermal treatment at 600°C. X-ray diffraction analyses showed that, for x ≤ 0.20, a solid solution Ce1- xBixO2-x/2 with fluorine structure was formed. For x ranging between 0.25 and 0.7, a tetragonal b’-Bi2O3 phase coexisting with the solid solution was observed. For x ranging between 0.8 and 0.9, a new tetragonal b'-Bi2O3 phase, closely related to the b' phase was evidenced. Finally, close to x=1, the classical monoclinic a-Bi2O3 structure crystallized. The formation of such intermediate tetragonal b and b’ phases could be due of theprobable presence of cerium cations in the Bi2O3 lattice. The solid–gas interactions between these polycristalline materials and air–CH4 and air–CO flows have been studied as a function of time, temperature and composition x, using Fourier transform infrared (FTIR) analyses of the conversions of CH4 and CO gases into the CO2 gas. For all compositions, a low catalytic reactivity was observed with air–CH4 gas flows, while, for the highest bismuth compositions, a high catalytic reactivity was observed with air–CO gas flows. The electrical conduction of this series of polycrystalline samples has been analyzed using electrical impedance spectroscopy, in the temperature range 25 to 750°C. To interpret the Nyquist representations of electrical analyses, various impedance models including constant phase elements and Warburg impedances have been used. The optimal conduction observed close to composition x=0.7 should be due to the stabilization of the tetragonal b’ Bi2O3 phase. This specific multiphase system could present a high interest in catalytic and electrolytic applications.

A Tomografia por Impedância elétrica (TIE) tem como objetivo gerar imagens da distribuição de resistividade dentro de um domínio. A TIE injeta correntes em eletrodos alocados na fronteira do domínio e mede potenciais elétricos através dos mesmos eletrodos. A TIE é considerada um problema inverso, não-linear e mal posto. Atualmente, para gerar uma solução do problema inverso, existem duas classes de algoritmos para estimar a distribuição de resistividade no interior do domínio, os que estimam variações da distribuição de resistividade do domínio e os absolutos, que estimam a distribuição de resistividade. Variações da distribuição de resistividade são o resultado da solução de um sistema linear do tipo Ax = b. O objetivo do presente trabalho é avaliar o desempenho da Programação Linear (PL) na solução do sistema linear, avaliar o algoritmo quanto a propaga- ção de erros numéricos e avaliar os efeitos de restringir o espaço solução através de restrições de PL. Os efeitos do uso de Programação Linear é avaliado tanto em métodos que geram imagens de diferenças, como o Matriz de Sensibilidade, como em métodos absolutos, como o Gauss-Newton. Mostra-se neste trabalho que o uso da PL diminui o erro numérico propagado quando comparado ao uso do algoritmo LU Decomposition. Resulta também que reduzir o espaço solução, diretamente através de restrições de PL, melhora a resolução em resistividade e a resolução espacial da imagem quando comparado com o uso de LU Decomposition. / Electrical impedance tomography (EIT) generates images of the resistivity distribution of a domain. The EIT method inject currents through electrodes placed on the boundary of the domain and measures electric potentials through the same electrodes. EIT is considered an inverse problem, non-linear and ill-conditioned. There are two classes of algorithms to estimate the resistivity distribution inside the domain, difference images algorithms, which estimate resistivity distribution variations, and absolute images algorithms, which estimate the resistivity distribution. Resistivity distribution variations are the solution of a linear system, say Ax = b. In this work, the main objective is to evaluate the performance of Linear Programming (LP) solving an EIT linear system from the point of view of the numerical error propagation and the ability to constrain the solution space. The impact of using LP to solve an EIT linear system is evaluated on a difference image algorithm and on an absolute algorithm. This work shows that the use of LP diminishes the numerical error propagation compared to LU Decomposition. It is also shown that constraining the solution space through LP improves the resistivity resolution and the spatial resolution of the images when compared to LU Decomposition.

A Tomografia por Impedância Elétrica (EIT) é um método que utiliza estimativas da distribuição de condutividade ou impedância de tecidos orgânicos na obtenção de imagens médicas. O procedimento de obtenção das imagens baseia-se em medições de correntes ou voltagens no contorno da região sob análise e na estimação de parâmetros de um modelo desta região. No caso de pacientes submetidos à respiração artificial, o conhecimento da distribuição absoluta ou das variações de condutividades nos pulmões auxilia na detecção de fenômenos como colapso alveolar ou pneumotórax e permite o ajuste e controle da vazão e pressão do ar fornecido, de modo a evitar a ocorrência de tais anomalias. Este trabalho apresenta algoritmos cujo objetivo é a solução do problema inverso e mal posto de estimar a distribuição absoluta e as variações de condutividades nos pulmões através da EIT para a geração de imagens em duas dimensões. O algoritmo para a estimação da distribuição absoluta de condutividade utiliza o filtro estendido de Kalman. As simulações numéricas mostram que, com medidas incorporando ruído cujo desvio padrão atinge até 12% da máxima voltagem, as estimativas de condutividades convergem para a distribuição esperada com um desvio inferior a 7% do valor da máxima condutividade. Quanto à detecção de variações de condutividades em relação a uma distribuição de condutividades tomada como referência, as simulações numéricas sugerem que a solução do problema depende da utilização de métodos de regularização. / Electrical Impedance Tomography (EIT) is a method that uses estimates of conductivity or impedance distribution in living tissues to generate medical images. The estimation procedure is based on measurements of electrical currents or voltages at the boundary of the region under analysis, and on the processing of these data through a proper algorithm. In patients under artificial ventilation, knowledge of absolute or relative conductivity distribution in the lungs helps detecting the presence of alveolar collapse or pneumothorax, and allows setting and controlling air volume and pressure of the ventilation device. This work presents algorithms that aim at solving the ill-posed inverse problem of estimating absolute and relative conductivity distribution in the lungs through EIT for cross-sectional image reconstruction. The algorithm for absolute conductivity distribution estimation uses the extended Kalman filter. Numerical simulations show that, when the standard deviation of the measurement noise level raises up to 12% of the maximal measured voltage, the conductivity estimates converge to the expected vector within 7% accuracy of the maximal conductivity value. Addressing the estimation of conductivity changes in relation to a conductivity distribution taken as reference, numerical simulations suggest that the problem may be properly solved using regularization methods.

Les systèmes piézoélectriques sont utilisés dans un grand nombre d'applications (mesures physiques, contrôle non destructif). Beaucoup d'entre elles nécessitent la mesure rapide de l'impédance électrique du capteur, particulièrement dans le cadre des microsystèmes. C'est pourquoi ce travail est consacré à la conception et au développement d'un analyseur d'impédance sur puce. L'analyseur est programmable en fréquence et en impédance et est implanté sur un système embarqué de type FPGA (field programmable gate array). Nous proposons trois méthodes à l'analyse leur impédance : une mesure ratiométrique, une modélisation paramétrique adaptative du capteur et une méthode originale utilisant l'asservissement de la tension d'excitation par un réseau résistif programmable. L'implantation des algorithmes sur la cible FPGA est réalisée selon une approche de type HIL (Hardware In the Loop) / The piezoelectric systems are used in many applications (physical measurements, non-destructive testing). Many of them require fast measurement of the sensor electrical impedance, particularly in the micro systems domain. Therefore this work is dedicated to the design and the development of an impedance analyzer on chip, programmable in frequency and impedance, and implantable in an embedded system of FPGA (field programmable gate array) type. We propose three methods for impedance analysis: a ratiometric measurement, an adaptive parametric modeling of the sensor, and an original method using the feedback control of the excitation voltage by a programmable resistive network. The implementation of algorithms on FPGA target is performed using HIL (Hardware In the Loop) approach

A Tomografia por Impedância Elétrica (EIT) é um método que utiliza estimativas da distribuição de condutividade ou impedância de tecidos orgânicos na obtenção de imagens médicas. O procedimento de obtenção das imagens baseia-se em medições de correntes ou voltagens no contorno da região sob análise e na estimação de parâmetros de um modelo desta região. No caso de pacientes submetidos à respiração artificial, o conhecimento da distribuição absoluta ou das variações de condutividades nos pulmões auxilia na detecção de fenômenos como colapso alveolar ou pneumotórax e permite o ajuste e controle da vazão e pressão do ar fornecido, de modo a evitar a ocorrência de tais anomalias. Este trabalho apresenta algoritmos cujo objetivo é a solução do problema inverso e mal posto de estimar a distribuição absoluta e as variações de condutividades nos pulmões através da EIT para a geração de imagens em duas dimensões. O algoritmo para a estimação da distribuição absoluta de condutividade utiliza o filtro estendido de Kalman. As simulações numéricas mostram que, com medidas incorporando ruído cujo desvio padrão atinge até 12% da máxima voltagem, as estimativas de condutividades convergem para a distribuição esperada com um desvio inferior a 7% do valor da máxima condutividade. Quanto à detecção de variações de condutividades em relação a uma distribuição de condutividades tomada como referência, as simulações numéricas sugerem que a solução do problema depende da utilização de métodos de regularização. / Electrical Impedance Tomography (EIT) is a method that uses estimates of conductivity or impedance distribution in living tissues to generate medical images. The estimation procedure is based on measurements of electrical currents or voltages at the boundary of the region under analysis, and on the processing of these data through a proper algorithm. In patients under artificial ventilation, knowledge of absolute or relative conductivity distribution in the lungs helps detecting the presence of alveolar collapse or pneumothorax, and allows setting and controlling air volume and pressure of the ventilation device. This work presents algorithms that aim at solving the ill-posed inverse problem of estimating absolute and relative conductivity distribution in the lungs through EIT for cross-sectional image reconstruction. The algorithm for absolute conductivity distribution estimation uses the extended Kalman filter. Numerical simulations show that, when the standard deviation of the measurement noise level raises up to 12% of the maximal measured voltage, the conductivity estimates converge to the expected vector within 7% accuracy of the maximal conductivity value. Addressing the estimation of conductivity changes in relation to a conductivity distribution taken as reference, numerical simulations suggest that the problem may be properly solved using regularization methods.

A Tomografia por Impedância Elétrica (TIE) é uma técnica não invasiva usada para produzir imagens que representam a distribuição de resistividade, ou condutividade, de uma seção transversal dentro de um domínio, por vezes o tórax humano, a partir do conhecimento de medidas elétricas feitas através de eletrodos distribuídos na sua fronteira. Correntes injetam-se e medem-se voltagens ou vice-versa. Distribuição de variação de resistividade ou distribuição de valor absoluto de resistividade podem ser estimadas, gerando algoritmos ditos de diferenças ou absolutos. O presente trabalho avalia o desempenho de um algoritmo probabilístico baseado no método Simulated Annealing (SA) para obter distribuições absolutas de resistividade em duas dimensões (2D). O SA difere dos métodos tradicionais de busca, tem a capacidade de escapar de mínimos locais graças ao emprego do critério de Metropolis para a aceitação dos novos pontos no espaço de busca e não precisa da avaliação de derivadas da função objetivo. O algoritmo desenvolvido soluciona o problema inverso da TIE ao resolver iterativamente um problema direto, utilizando distribuições de resistividade obtidas por sorteio aleatório. O sorteio é realizado pelo algoritmo de Metropolis. Na ausência de regularizações, assume-se que a imagem sorteada que minimiza a diferença entre as voltagens medidas na fronteira do domínio e as calculadas é a que mais se aproxima da distribuição de resistividade real. Neste sentido, a imagem final maximiza a verossemelhança. Este trabalho contribui com o desenvolvimento de algoritmos para estimação de imagem aplicados para monitorar a ventilação mecânica dos pulmões. Uma vez que se pretende resolver um problema inverso, não-linear e mal-posto é necessário introduzir informação a priori, na forma de restrições do espaço solução ou de regularizações. São realizados ensaios com dados simulados por meio de um fantoma numérico, dados de bancada experimental e dados provenientes de um tórax humano. Os resultados mostram que a localização, o tamanho e a resistividade do objeto estão dentro da precisão da TIE obtida por métodos clássicos, mas o esforço computacional é grande. Verificam-se, assim, as vantagens e a viabilidade do algoritmo proposto. / The Electrical Impedance Tomography (EIT) is a non-invasive technique used to produce images that represent the cross-sectional electrical resistivity distribution, or conductivity, within a domain, for instance the human thorax, from electrical measurements made through electrodes distributed on its boundary. Currents are injected and voltages measured, or vice-versa. Distributions of resistivity variations or distributions of absolute resistivity can be estimated, producing difference or absolute algorithms. The present work develops and evaluates the performance of a probabilistic algorithm based on the Simulated Annealing method (SA) to obtain absolute resistivity distributions in two dimensions (2D). The SA differs from the traditional search methods, no evaluation of objective function derivatives is required and it is possible to escape from local minima through the use of the Metropolis criterion for acceptance of new points in the search space. The developed algorithm solves the inverse problem of EIT by solving iteratively a direct problem, using random resistivity distributions. The random search is accomplished by the Metropolis algorithm. In the absence of regularizations, it is assumed that the resistivity distribution, an image, that minimizes the difference between the measured electrical potentials on the boundary and computed electrical potentials is the closest to the real resistivity distribution. In this sense, the algorithm maximizes the likelihood. This work contributes to the development of image estimation algorithms applied to lung monitoring, for instance, during mechanical ventilation. To solve this non-linear ill-posed inverse problem it is necessary to introduce prior information in the form of restrictions of the solution space or regularization techniques. The tests are carried out using simulated data obtained from a numerical phantom, an experimental phantom and human thorax data. The results show that the localization of an object, the size of an object and the resistivity of an object are within the accuracy of EIT obtained by classical methods, but the computational effort is large. The advantages and feasibility of the proposed algorithm were investigated.

Magnetic Resonance Electrical Impedance Mammography (MREIM) is a new imaging technique under development by Wollin Ventures, Inc. in conjunction with the H. Lee Moffitt Cancer Center & Research Institute. MREIM addresses the problem of low specificity of magnetic resonance mammography and high false-positive rates, which lead to unnecessary biopsies. Because cancerous tissue has a higher electrical conductivity than benign tissue, it may serve as a biomarker for differentiation between malignant and benign lesions. The MREIM principle is based on measuring both magnetic resonance and electric properties of the breast by adding a quasi-steady-state electric field to the standard magnetic resonance breast image acquisition. This applied electric field produces a current density that creates an additional magnetic field that in turn alters the native magnetic resonance signal in areas of higher electrical conductivity, corresponding to cancerous tissue. This work comprises MREIM theory, computer simulations, and experimental developments. First, a general overview and background review of tissue modeling and electrical-impedance imaging techniques are presented. The experimental part of this work provides a description of the MREIM apparatus and the imaging results of a custom-made breast phantom. This phantom was designed and developed to mimic the magnetic resonance and electrical properties of the breast. The theoretical part of this work provides an extension to the initial MREIM theoretical developments to further understand the MREIM effects. MREIM computer simulations were developed for both idealized and realistic tumor models. A method of numerical calculation of electric potential and induced magnetic field distribution in objects with irregular boundaries and anisotropic conductivity was developed based on the Finite Difference Method. Experimental findings were replicated with simulations. MREIM effects were analyzed with contrast diagrams to show the theoretical perceptibility as a function of the acquisition parameters. An important goal was to reduce the applied current. A new protocol for an MREIM sequence is suggested. This protocol defines parameters for the applied current synchronized to a specific magnetic resonance imaging sequence. A simulation utilizing this protocol showed that the MREIM effect is detectable for a 3-mm-diameter tumor with a current density of 0.5 A/m², which is within acceptable limits.

Electrical Impedance Spectroscopy (EIS) is a relatively new method applied to food quality assessment. EIS allows relatively inexpensive assessment, is fast, easy to operate and non-invasive. It has been adopted for investigation of fundamental electrical properties of plant tissues. Although the applications of EIS for food quality determination have been reported previously, the analytical relationships between electrical impedance properties and quality criteria have not yet been fully developed. Further exploration is thus important in acquiring more data on electrical impedance characteristics of fruits and vegetables and researching new approaches for determination of their quality. This dissertation aims to investigate the electrical impedance properties of fruits and vegetables, and explore the relationship between impedance and quality criteria. In particular, the present dissertation outlines experimental research conducted on relationships between impedance properties and fruit tastes as well as the impedance changes observed during ripening process. Impedance measurement to monitor moisture content changes in the progress of drying is also included in this research. In summary, the impedance properties have merits in fruits and vegetables quality assessment. The current used subjective visual inspection and assessment could be replaced by the EIS based approach as it is a more precise measurement of food quality. Further study is required to give this method practical value.