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Résolution de problèmes de rayonnement électromagnétique appliqués à l’imagerie médicale avec FreeFEM++

Abstract : The use of microwaves for diagnosis is booming in the medical field. One of the latest applications is the detection of strokes by microwave imaging. The company EMTensor GmbH based in Vienna, Austria is currently studying such a system in collaboration with LEAT, the LJAD of the Côte d’Azur University and the LJLL of Sarbonne University, for the diagnosis and control of the treatement efficiency. The purpose of this work is to model the brain imaging measurement system developed by EMTensor GmbH. It is a transmission/ reception system consisting of 160 antennas arranged in 5 rings of 32 antennas distributed on a cylinder metal tank of semi-open circular section. One of the major issues of this work is the modeling and electromagnetic simulation (EM) of the complete system including a realistic brain model. The difficulty lies both in the size of the EM problem to be simulated beacause of the relationship between the considerable size of the system and the the very small size of certain inhomogeneities within the brain, and the great heterogeneity of the dielectric permittivities present inside the brain. We decided to use an open source software, FreeFem++ for this modelling because it is well adapted to high performance computing through domain decomposition methods, which is mandatory for the complexity of the EM problem. First, we compared the simulation results of the vacuum matching measurement system (without the brain) to the measurements and the results obtained by the FEM-based EM HFSS simulation software to those obtained by FreeFem++. We then simulated a virtual threedimensional head model, from brain imaging system cuts (CT scan and MRI), in partnership with EMTensor, looking for the position and type of stroke (ischemic and hemorragic). The influence of the measurement noise, the value of the adaptation gel used, the coupling between the sensors and the coupling between the head and the sensors are also studied. In order to validate these models, two simple cases have been studied. A large tube and a small plastic tube are fielld with adaptation liquid with the dielectric characteristic of a brain to find the shape of the tubes used by qualitative imaging. Finally, with the MEDIMAX project partners and the EMTensor company we applied a quantitative method to the detection of ischemic stroke by the microwave tomography. The direct problem has been solved with the help of FreeFem++, using hight order elements and parallel preconditioners for the domain decomposition method. We solved the inverse problem by a minimization algorithm, in order to reconstruct tomographic images of the brain in times compatible with medical imperatives defined by clinicians.”
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https://tel.archives-ouvertes.fr/tel-02349123
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Submitted on : Tuesday, November 5, 2019 - 3:24:18 PM
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  • HAL Id : tel-02349123, version 1

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Ibtissam El Kanfoud. Résolution de problèmes de rayonnement électromagnétique appliqués à l’imagerie médicale avec FreeFEM++. Electronique. Université Côte d'Azur, 2019. Français. ⟨NNT : 2019AZUR4000⟩. ⟨tel-02349123⟩

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