Les cavités latérales sont des zones mortes à surface libre situées sur le côté d’un écoulement fluvial ou côtier. Les vitesses caractéristiques au sein de la cavité étant beaucoup plus faibles que celles de l’écoulement, une couche de mélange se développe à l’interface entre ces deux régions. Cette couche de mélange peut alors transférer de la quantité de mouvement de l’écoulement vers la cavité et ainsi mettre en mouvement la cavité et peut aussi transférer de la masse entre les deux régions, telle une pollution venant de l’écoulement amont. L’étude de cette thèse a alors consisté à étudier les caractéristiques de la couche de mélange, qui est rendue spécifique par le fait qu’elle se développe entre deux coins géométriques formés par l’intersection entre les parois de la cavité et celles de l’écoulement principal. Nous avons alors pu identifier l’origine et l’alternance des mouvements de fluide dans la direction transverse: de la cavité vers l’écoulement et inversement. Concernant la mise en mouvement de la cavité, le choix a été fait de considérer un écoulement principal fixé et de modifier l’extension de la cavité dans la direction perpendiculaire à l’écoulement, passant ainsi d’une cavité rectangulaire alignée avec l’écoulement principal à une cavité allongée dans le sens opposé. La mesure de champ de vitesse par PIV 2D a alors montré une forte évolution de la forme de l’écoulement à mesure que la géométrie de la cavité évolue : un système avec deux cellules alignées dans le sens de l’écoulement à un système à une seule cellule, puis un système à deux cellules et enfin un système complexe 3D ont ainsi été observés pour une cavité de plus en plus allongée. Ensuite, une modification du dispositif expérimental a permis de mesurer de deux façons différentes le transport de scalaire de l’écoulement principal vers la cavité, de comprendre les processus associés à ce transfert et enfin de quantifier cette capacité de transfert pour différents écoulements principaux et différentes géométries de cavités. Nous avons notamment montré que la géométrie de la cavité a peu d’effet alors que le nombre de Reynolds et la profondeur d’eau normalisée ont un effet majeur sur cette capacité de transfert de masse entre les deux régions. / Lateral cavities are free-surface dead-zones located on the side of a fluvial or coastal main flow. As the typical velocities are much larger in the main flow than in the cavity, a mixing layer appears at the interface between both regions. This mixing layer is able to transfer between the main flow and the cavity momentum which then sets the fluid in the cavity in motion and also passive scalar, such as a pollution coming from upstream. The objective of this work was then to investigate the characteristics of the mixing layer, which specificity comes from the fact that it is constrained between the upstream and downstream geometrical corners. It was possible to observe the origin and alternation of the transversal fluid motions: from the cavity towards the main flow and conversely. Regarding the motion in the cavity, the choice was made to keep a constant main flow and to measure the 2D horizontal velocity field using PIV as the extension of the cavity increases. The flow pattern then passes from a 2-cell patterns aligned in the direction of the main flow to a single-cell pattern, then a 2-cells patterns aligned along the direction perpendicular to the main flow and finally a complex 3D pattern for the widest cavity. Then a modification of the experimental set-up permitted to investigate the passive scalar exchanges from the main stream towards the cavity. It was possible to understand the processes responsible for such transfer and to quantify the transfer capacity. The analysis dimensional revealed that in the present subcritical, smooth simplified geometry cavity, the three parameters possible responsible for the modification of the transfer capacity are the geometrical aspect ratio of the cavity, the Reynolds number of the main flow and finally the normalized water depth. It was then shown that the impact of the cavity geometry remains negligible but that the Reynolds number and the normalized water do impact this passive scalar transfer capacity.

INTRODUÇÃO: Epilepsia do lobo temporal mesial (ELTM) por esclerose hipocampal (EH) é a forma de epilepsia focal mais comum na idade adulta e a causa mais frequente de refratariedade ao tratamento clínico. Apesar de se tratar de uma patologia da substância cinzenta, alguns estudos, por meio da imagem por tensor de difusão (diffusion tensor imaging-DTI), têm demonstrado alteração da substância branca temporal e extratemporal nestes pacientes. O corpo caloso (CC) é a maior comissura cerebral conectando áreas corticais homólogas de ambos os hemisférios cerebrais e tem sido implicado na propagação da atividade epiléptica. O objetivo principal do presente estudo foi avaliar possíveis alterações no CC de pacientes com ELTM-EH pela técnica de DTI e verificar se essas dependem da lateralidade da EH e da concordância entre os exames de ressonância magnética (RM) e os exames de vídeo-eletroencefalograma (EEG). Como objetivo secundário, também avaliou-se se estas alterações se correlacionavam com alguma variável clínica ou com as medidas volumétricas do CC. MÉTODOS: 42 pacientes com ELTM-EH (idades: 20-54 anos) e 30 voluntários saudáveis como grupo controle (idades: 18-53 anos) realizaram exame de RM de crânio, sendo obtidas sequências de DTI com 32 direções de gradiente e imagens volumétricas ponderadas em T1. Os pacientes foram também divididos em subgrupos: EH à direita e EH à esquerda, e em pacientes concordantes e discordantes. Os valores de anisotropia fracionada (AF), difusividade média (DM), difusividade axial (DA), difusividade radial (DR) e os dados volumétricos foram extraídos a partir de cinco segmentos obtidos automaticamente na secção sagital do CC. Foram realizadas comparações dos parâmetros de DTI no CC entre os grupos de pacientes e controles, e entre os subgrupos de pacientes. Foram investigadas correlações entre os parâmetros do tensor de difusão e as variáveis clínicas. As alterações volumétricas no CC dos pacientes com ELTM-EH bem como a correlação dessas alterações com as anormalidades de difusão também foram avaliadas. Considerou-se um valor de p < 0,05 como estatisticamente significativo. RESULTADOS: Nas regiões anterior, médio-posterior e posterior do CC dos pacientes, observaram-se redução da AF e aumento da DM e da DR, em relação aos controles. A DA manteve-se inalterada. Não foram demonstradas diferenças nos padrões de alteração de difusão entre os pacientes com EH à direita e com EH à esquerda, nem entre pacientes concordantes e discordantes. Não foram observadas correlações significativas entre os parâmetros do tensor de difusão com a idade ao evento inicial, idade de início da epilepsia, tempo de doença, tempo de epilepsia, período de latência e frequência de crises. No entanto, pacientes que apresentaram crise febril como evento precipitante inicial exibiram maior intensidade e extensão das alterações de difusão. Observou-se redução volumétrica difusa do CC, sendo demonstrada correlação negativa significativa entre DM e DR, e o volume nos segmentos central, médio-posterior e posterior, e, ainda, entre DA e volume do segmento posterior. Nós observamos, ainda, correlação negativa significativa entre o volume e o tempo de epilepsia, e o tempo de doença. CONCLUSÕES: Houve alteração dos parâmetros de DTI em áreas específicas do CC e redução volumétrica difusa desta estrutura. Tais anormalidades parecem ser secundárias à propagação das crises epilépticas ao longo de vias específicas anatômica ou funcionalmente relacionadas aos lobos temporais promovendo alterações secundárias na substância branca cerebral. O histórico de crise febril está relacionado a maior intensidade e extensão de acometimento do CC / INTRODUCTION: Mesial temporal lobe epilepsy (MTLE) with hippocampal sclerosis (HS) is the most common form of focal epilepsy in adults and it is frequently associated with refractoriness to medical treatment. Although epilepsy is considered a grey-matter disease, abnormalities in the temporal and extra-temporal white matter have been identified in these patients with diffusion tensor imaging (DTI). The corpus callosum (CC) is the major white matter tract connecting both cerebral hemispheres and has been implicated as an important route of spread of epileptic activity. The first goal of this study was to detect DTI abnormalities in specific areas of the CC in patients with MTLE-HS and to verify if these abnormalities depend on the laterality of the HS and on the concordance between the magnetic resonance imaging (MRI) and video-electroencephalogram (EEG). As a second goal we assessed if DTI results were correlated with any clinical variable or volumetric changes of the CC. METHODS: 42 patients (age: 20-54 years) and 30 healthy controls (age:18-53 years) were submitted to brain MRI. DTI sequences with 32 gradient encoding directions and volumetric T1-weighted images were obtained. Additionally, we grouped the patients in left sided and right sided HS and in concordant and discordant HS. Mean values of fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), radial diffusivity (RD) and volumetric results were extracted from five segments at the midsagittal section of the CC obtained through automatic segmentation. Comparisons of DTI parameters of the CC were performed between patients and controls and between subgroups of patients. Correlations between DTI parameters and clinical findings were calculated. We also evaluated volume abnormalities of the CC in MTLE-HS patients and the correlations between these abnormalities and DTI changes. We considered a value of p <0.05 statistically significant. RESULTS: Our study showed that, when HS patients was compared to controls, the FA was lowest in the anterior, mid-posterior and posterior subregions of the CC. MD and RD were higher in these same segments. No changes were observed in AD. No differences in the CC DTI parameters were detected between right-sided HS and left-sided HS or between concordant and discordant HS patients. Age at initial event, age at epilepsy onset, duration of disease, duration of epilepsy, latency period and seizure frequency were not significantly correlated with the DTI parameters. However, patients who had febrile seizures as initial event exhibited greater intensity and extent of DTI changes. All segments demonstrated volume reduction compared to controls. Significant negative correlation was demonstrated between MD and RD and the volume in the central, midposterior and posterior segments of the CC, and between AD and volume of the posterior segment. We also demonstrated negative correlation between volume and duration of disease and duration of epilepsy. CONCLUSIONS: This study showed diffusion abnormalities in specific areas of the CC and diffuse atrophy in patients with unilateral HS, which may be secondary to seizures propagation along specific pathways leading to secondary changes in brain white matter. The history of febrile seizure is related to greater involvement of the CC

INTRODUÇÃO: Epilepsia do lobo temporal mesial (ELTM) por esclerose hipocampal (EH) é a forma de epilepsia focal mais comum na idade adulta e a causa mais frequente de refratariedade ao tratamento clínico. Apesar de se tratar de uma patologia da substância cinzenta, alguns estudos, por meio da imagem por tensor de difusão (diffusion tensor imaging-DTI), têm demonstrado alteração da substância branca temporal e extratemporal nestes pacientes. O corpo caloso (CC) é a maior comissura cerebral conectando áreas corticais homólogas de ambos os hemisférios cerebrais e tem sido implicado na propagação da atividade epiléptica. O objetivo principal do presente estudo foi avaliar possíveis alterações no CC de pacientes com ELTM-EH pela técnica de DTI e verificar se essas dependem da lateralidade da EH e da concordância entre os exames de ressonância magnética (RM) e os exames de vídeo-eletroencefalograma (EEG). Como objetivo secundário, também avaliou-se se estas alterações se correlacionavam com alguma variável clínica ou com as medidas volumétricas do CC. MÉTODOS: 42 pacientes com ELTM-EH (idades: 20-54 anos) e 30 voluntários saudáveis como grupo controle (idades: 18-53 anos) realizaram exame de RM de crânio, sendo obtidas sequências de DTI com 32 direções de gradiente e imagens volumétricas ponderadas em T1. Os pacientes foram também divididos em subgrupos: EH à direita e EH à esquerda, e em pacientes concordantes e discordantes. Os valores de anisotropia fracionada (AF), difusividade média (DM), difusividade axial (DA), difusividade radial (DR) e os dados volumétricos foram extraídos a partir de cinco segmentos obtidos automaticamente na secção sagital do CC. Foram realizadas comparações dos parâmetros de DTI no CC entre os grupos de pacientes e controles, e entre os subgrupos de pacientes. Foram investigadas correlações entre os parâmetros do tensor de difusão e as variáveis clínicas. As alterações volumétricas no CC dos pacientes com ELTM-EH bem como a correlação dessas alterações com as anormalidades de difusão também foram avaliadas. Considerou-se um valor de p < 0,05 como estatisticamente significativo. RESULTADOS: Nas regiões anterior, médio-posterior e posterior do CC dos pacientes, observaram-se redução da AF e aumento da DM e da DR, em relação aos controles. A DA manteve-se inalterada. Não foram demonstradas diferenças nos padrões de alteração de difusão entre os pacientes com EH à direita e com EH à esquerda, nem entre pacientes concordantes e discordantes. Não foram observadas correlações significativas entre os parâmetros do tensor de difusão com a idade ao evento inicial, idade de início da epilepsia, tempo de doença, tempo de epilepsia, período de latência e frequência de crises. No entanto, pacientes que apresentaram crise febril como evento precipitante inicial exibiram maior intensidade e extensão das alterações de difusão. Observou-se redução volumétrica difusa do CC, sendo demonstrada correlação negativa significativa entre DM e DR, e o volume nos segmentos central, médio-posterior e posterior, e, ainda, entre DA e volume do segmento posterior. Nós observamos, ainda, correlação negativa significativa entre o volume e o tempo de epilepsia, e o tempo de doença. CONCLUSÕES: Houve alteração dos parâmetros de DTI em áreas específicas do CC e redução volumétrica difusa desta estrutura. Tais anormalidades parecem ser secundárias à propagação das crises epilépticas ao longo de vias específicas anatômica ou funcionalmente relacionadas aos lobos temporais promovendo alterações secundárias na substância branca cerebral. O histórico de crise febril está relacionado a maior intensidade e extensão de acometimento do CC / INTRODUCTION: Mesial temporal lobe epilepsy (MTLE) with hippocampal sclerosis (HS) is the most common form of focal epilepsy in adults and it is frequently associated with refractoriness to medical treatment. Although epilepsy is considered a grey-matter disease, abnormalities in the temporal and extra-temporal white matter have been identified in these patients with diffusion tensor imaging (DTI). The corpus callosum (CC) is the major white matter tract connecting both cerebral hemispheres and has been implicated as an important route of spread of epileptic activity. The first goal of this study was to detect DTI abnormalities in specific areas of the CC in patients with MTLE-HS and to verify if these abnormalities depend on the laterality of the HS and on the concordance between the magnetic resonance imaging (MRI) and video-electroencephalogram (EEG). As a second goal we assessed if DTI results were correlated with any clinical variable or volumetric changes of the CC. METHODS: 42 patients (age: 20-54 years) and 30 healthy controls (age:18-53 years) were submitted to brain MRI. DTI sequences with 32 gradient encoding directions and volumetric T1-weighted images were obtained. Additionally, we grouped the patients in left sided and right sided HS and in concordant and discordant HS. Mean values of fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), radial diffusivity (RD) and volumetric results were extracted from five segments at the midsagittal section of the CC obtained through automatic segmentation. Comparisons of DTI parameters of the CC were performed between patients and controls and between subgroups of patients. Correlations between DTI parameters and clinical findings were calculated. We also evaluated volume abnormalities of the CC in MTLE-HS patients and the correlations between these abnormalities and DTI changes. We considered a value of p <0.05 statistically significant. RESULTS: Our study showed that, when HS patients was compared to controls, the FA was lowest in the anterior, mid-posterior and posterior subregions of the CC. MD and RD were higher in these same segments. No changes were observed in AD. No differences in the CC DTI parameters were detected between right-sided HS and left-sided HS or between concordant and discordant HS patients. Age at initial event, age at epilepsy onset, duration of disease, duration of epilepsy, latency period and seizure frequency were not significantly correlated with the DTI parameters. However, patients who had febrile seizures as initial event exhibited greater intensity and extent of DTI changes. All segments demonstrated volume reduction compared to controls. Significant negative correlation was demonstrated between MD and RD and the volume in the central, midposterior and posterior segments of the CC, and between AD and volume of the posterior segment. We also demonstrated negative correlation between volume and duration of disease and duration of epilepsy. CONCLUSIONS: This study showed diffusion abnormalities in specific areas of the CC and diffuse atrophy in patients with unilateral HS, which may be secondary to seizures propagation along specific pathways leading to secondary changes in brain white matter. The history of febrile seizure is related to greater involvement of the CC

L'un des problèmes fondamentaux de l'imagerie cardiaque par résonance magnétique du tenseur de diffusion (IRM-TD) est sa faible résolution spatiale, à cause des limitations matérielles des scanners IRM actuels. L'objectif principal de ce travail de thèse est de développer de nouvelles approches pour améliorer la résolution des données d'IRM-TD afin de mieux représenter l'architecture myocardique du coeur humain et de la comparer avec des résultats issus d'autres techniques d'investigation telles que l'imagerie par lumière polarisée. Dans ce cadre, le travail porte sur trois parties principales. La première concerne le développement d'une nouvelle approche pour l'interpolation des champs de vecteurs propres principaux issus de l'IRM-TD cardiaque humaine. Cette approche consiste d'abord à supprimer les vecteurs corrompus par le bruit au lieu de débruiter de manière uniforme le champ entier de vecteurs, et ensuite à interpoler le champ de vecteurs en utilisant la modèle Thin-Plate-Spline (TPS) afin d'exploiter la corrélation entre les composantes du vecteur. La deuxième partie concerne une nouvelle famille de méthodes d'interpolation pour les champs de tenseurs, basée soit sur les angles d'Euler soit sur le quaternion. Ces méthodes exploitent les caractéristiques du tenseur et préservent les paramètres de tenseurs, tels que le déterminant du tenseur, l'anisotropie fractionnelle (FA) et la diffusivité moyenne (MD). En outre, cette partie compare les principales approches d'interpolation au niveau des images pondérées en diffusion et des champs de tenseurs, et les résultats montrent qu'il serait préférable d'effectuer l'interpolation des données d'IRM-TD au niveau des champs de tenseurs. La troisième partie étudie le changement des paramètres MD et FA après un infarctus du myocarde chez les cochons, et l'influence des méthodes d'interpolation sur ces paramètres dans la zone infarctus et la zone distante. Les résultats montrent que la zone infarctus présente une diminution significative de FA et une augmentation significative de MD, comparée avec la zone distante, et que les méthodes d'interpolations du tenseur ont plus d'influence sur FA que sur MD, ce qui suggère que l'interprétation de ces paramètres cliniques après l'interpolation doive être prise avec précaution. / One of fundamental problems in human cardiac diffusion tensor magnetic resonance imaging (DT-MRI) is its poor spatial resolution, due to the hardware limitations of MRI scanners. The main purpose of this PhD work is to develop new approaches to improving the resolution of cardiac DT-MRI data in order to better understand the myocardial architecture of the heart and compare it with results issues from other investigation techniques such as polarized light imaging. Within this framework, the present work is composed of three main parts. The first part concerns a new approach to interpolating primary eigenvector fields from human cardiac DT-MRI using Thin Plate Spline (TPS) model. This approach removes the noise-corrupted vectors rather than denoising the whole vector field in a uniform manner, and uses TPS model in order to exploit the correlation between vector components during interpolation. The second part is dealt with a new category of feature-based methods for diffusion tensor field interpolation using either Euler angles or quaternion. These feature-based methods well preserve tensor parameters, such as tensor determinant, fractional anisotropy (FA) and mean diffusivity (MD) values. In this part are also compared the main interpolation approaches at the level of diffusion weighted images and tensor fields. The results show that the interpolation of DT-MRI data should be performed at the level of tensor fields. The last part investigates changes in MD and FA after myocardial infarction in porcine hearts, and the influence of diffusion tensor interpolation methods on FA and MD in both infarction and remote region. It is found that the infarction region showed significantly decreased FA and increased MD than the remote region, and that diffusion tensor interpolations have more significant influence on FA than on MD, which suggests that precaution should be taken when performing the clinical analysis based on the parameters after diffusion tensor interpolations.