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Introduction : La vitamine D (VitD) maintient la santé osseuse et influence le mouvement dentaire orthodontique (MDO). L’objectif était d’évaluer l’effet de la VitD sur la morphométrie osseuse, puis sur la vitesse et la stabilité du MDO. Méthode : 32 rats Sprague Dawley mâles ont été assignés à deux groupes expérimentaux, traités avec la VitD par gavage (systémique) ou par injection (locale), et deux groupes contrôles respectifs traités avec un tampon phosphate salin (PBS) pour 47 jours. Le MDO était effectué pendant 7 jours avec un ressort NiTi attaché entre la première molaire supérieure et les incisives. Un scan Micro-CT était réalisé à 5 temps : T0 (avant l’administration de VitD), T1 (début du MDO), T2 (fin du MDO), T3 (7 jours post-MDO), T4 (30 jours post-MDO). La vitesse et la stabilité du MDO étaient évaluées. La morphométrie osseuse a été analysée via la densité minérale osseuse (BMD), le pourcentage de volume d’os (BV/TV), la porosité totale (Po(tot)), le facteur du patron trabéculaire (Tb.Pf), l’index de structure du modèle (SMI) et la densité de connectivité (Conn.Dn). Résultats : Le groupe VitD systémique a montré une vitesse diminuée du MDO, mais une récidive inférieure au contrôle ainsi qu’une augmentation de la BMD et du BV/TV, et une diminution de la Po(tot) (p<0.05). La structure osseuse apparaissait plus fragmentée et présentait une Conn.Dn plus basse (p<0.05). Aucune différence n’a été trouvée entre le groupe administration locale de VitD et les autres groupes. Conclusion : L’administration systémique de VitD a engendré une diminution de vitesse du MDO en induisant plus de résistance, mais a aussi contribué à une meilleure stabilité grâce à une densité osseuse plus élevée. / Introduction: Vitamin D (VitD) maintains bone health and may influence the orthodontic tooth movement (OTM). The objective was to evaluate VitD effect on bone morphometry, and on the rate and stability of OTM. Methods: 32 male Sprague Dawley rats were assigned into two experimental groups, treated with VitD by gavage (systemic) or by injection (local), and two respective control groups treated with phosphate-buffered saline (PBS) for 47 days. OTM was performed for 7 days with a NiTi coil bonded between the upper first molar and incisors. Micro-CT scanning was performed at 5 time-points: T0 (before administration of VitD), T1 (start of OTM), T2 (end of OTM), T3 (7 days post-OTM) and T4 (30 days postOTM). Rate and stability of OTM were assessed. Bone morphometry was analyzed by bone mineral density (BMD), percent bone/volume (BV/TV), total porosity (Po(tot)), trabecular pattern factor (Tb.Pf), structure model index (SMI) and connectivity density (Conn.Dn). Results: The systemic VitD group showed a lower OTM rate, but also a lower relapse than control (p<0.05). It also demonstrated an increase of BMD and BV/TV, and a decrease of Po(tot) (p<0.05). The bone structure appeared more fragmented and presented lower Conn.Dn than the control (p<0.05). No statistical difference was found between VitD local administration and the other groups for the rate and stability of OTM, or for the bone morphometry. Conclusion: The systemic administration of VitD caused a decrease of OTM rate by generating more bone resistance, but also contributed to a greater stability due to a higher bone mineral density.

[pt] A microtomografia computadorizada de uma amostra de rocha possibilita uma caracterização do meio poroso e pode ser utilizada para estimar propriedades da rocha em macroescala, isto é, em escala de reservatório. Métodos baseados em mapas de distâncias e em algoritmos de erosão são as principais abordagens utilizadas para extração de uma rede de poros e gargantas a partir de imagens microtomográficas de rocha. Este trabalho propõe um método híbrido para a construção da rede, de modo que, durante o processo de modelagem na escala de poros, obtemos um esqueleto do espaço poroso por meio de um algoritmo de erosão e utilizamos um mapa de distâncias para construir uma rede de poros e gargantas. A determinação dos poros e gargantas a partir do esqueleto adota uma abordagem não-determinística possibilitando a geração de múltiplas redes com configurações distintas a partir de um mesmo esqueleto. Avaliamos a variabilidade dos cenários gerados e comparamos as estimativas para as propriedades petrofísicas com as obtidas pelo método de Bolas Máximas por meio dos resultados de uma simulação de fluxo monofásica na rede. / [en] Computerized microtomography of a rock sample enables a characterization of the porous medium and can be used to estimate rock properties at the macro-scale, i.e., reservoir-scale. Methods based on distance maps and thinning algorithms are the main approaches used for extracting a pore and throats network from microtomographic rock images. This paper proposes a hybrid method for constructing the network. So that during the pore-scale modeling process, we obtain a skeleton of the pore space by using a thinning algorithm and a distance map to build a network of pores and throats. The determination of pores and throats from the skeleton assumes a non-deterministic approach enabling the generation of multiple networks with distinct configurations from the same skeleton. We evaluate the variability of the generated scenarios and compare the estimates for the petrophysical properties with those obtained by the Maximum Ball Method through the results of a single-phase flow simulation on the network.

L’imagerie par contraste de phase suscite un intérêt croissant dans le domaine biomédical, puisqu’il offre un contraste amélioré par rapport à l’imagerie d’atténuation conventionnelle. En effet, le décalage en phase induit par les tissus mous, dans la gamme d’énergie utilisée en imagerie, est environ mille fois plus important que leur atténuation. Le contraste de phase peut être obtenu, entre autres, en laissant un faisceau de rayons X cohérent se propager librement après avoir traversé un échantillon. Dans ce cas, les signaux obtenus peuvent être modélisés par la diffraction de Fresnel. Le défi de l’imagerie de phase quantitative est de retrouver l’atténuation et l’information de phase de l’objet observé, à partir des motifs diffractés enregistrés à une ou plusieurs distances. Ces deux quantités d’atténuation et de phase, sont entremêlées de manière non-linéaire dans le signal acquis. Dans ces travaux, nous considérons les développements et les applications de la micro- et nanotomographie de phase. D’abord, nous nous sommes intéressés à la reconstruction quantitative de biomatériaux à partir d’une acquisition multi-distance. L’estimation de la phase a été effectuée via une approche mixte, basée sur la linéarisation du modèle de contraste. Elle a été suivie d’une étape de reconstruction tomographique. Nous avons automatisé le processus de reconstruction de phase, permettant ainsi l’analyse d’un grand nombre d’échantillons. Cette méthode a été utilisée pour étudier l’influence de différentes cellules osseuses sur la croissance de l’os. Ensuite, des échantillons d’os humains ont été observés en nanotomographie de phase. Nous avons montré le potentiel d’une telle technique sur l’observation et l’analyse du réseau lacuno-canaliculaire de l’os. Nous avons appliqué des outils existants pour caractériser de manière plus approfondie la minéralisation et les l’orientation des fibres de collagènes de certains échantillons. L’estimation de phase, est, néanmoins, un problème inverse mal posé. Il n’existe pas de méthode de reconstruction générale. Les méthodes existantes sont soit sensibles au bruit basse fréquence, soit exigent des conditions strictes sur l’objet observé. Ainsi, nous considérons le problème inverse joint, qui combine l’estimation de phase et la reconstruction tomographique en une seule étape. Nous avons proposé des algorithmes itératifs innovants qui couplent ces deux étapes dans une seule boucle régularisée. Nous avons considéré un modèle de contraste linéarisé, couplé à un algorithme algébrique de reconstruction tomographique. Ces algorithmes sont testés sur des données simulées. / Phase contrast imaging has been of growing interest in the biomedical field, since it provides an enhanced contrast compared to attenuation-based imaging. Actually, the phase shift of the incoming X-ray beam induced by an object can be up to three orders of magnitude higher than its attenuation, particularly for soft tissues in the imaging energy range. Phase contrast can be, among others existing techniques, achieved by letting a coherent X-ray beam freely propagate after the sample. In this case, the obtained and recorded signals can be modeled as Fresnel diffraction patterns. The challenge of quantitative phase imaging is to retrieve, from these diffraction patterns, both the attenuation and the phase information of the imaged object, quantities that are non-linearly entangled in the recorded signal. In this work we consider developments and applications of X-ray phase micro and nano-CT. First, we investigated the reconstruction of seeded bone scaffolds using sed multiple distance phase acquisitions. Phase retrieval is here performed using the mixed approach, based on a linearization of the contrast model, and followed by filtered-back projection. We implemented an automatic version of the phase reconstruction process, to allow for the reconstruction of large sets of samples. The method was applied to bone scaffold data in order to study the influence of different bone cells cultures on bone formation. Then, human bone samples were imaged using phase nano-CT, and the potential of phase nano-imaging to analyze the morphology of the lacuno-canalicular network is shown. We applied existing tools to further characterize the mineralization and the collagen orientation of these samples. Phase retrieval, however, is an ill-posed inverse problem. A general reconstruction method does not exist. Existing methods are either sensitive to low frequency noise, or put stringent requirements on the imaged object. Therefore, we considered the joint inverse problem of combining both phase retrieval and tomographic reconstruction. We proposed an innovative algorithm for this problem, which combines phase retrieval and tomographic reconstruction into a single iterative regularized loop, where a linear phase contrast model is coupled with an algebraic tomographic reconstruction algorithm. This algorithm is applied to numerical simulated data.

This thesis presents the development of a new multiscale stochastic fracture mechanics modelling framework informed by in-situ X-ray Computed Tomography (X-ray CT) tests, which can be used to enhance the quality of new designs and prognosis practices for fibre reinforced composites. To reduce the empiricism and conservatism of existing methods, this PhD research systematically has tackled several challenging tasks including: (i) extension of the cohesive interface crack model to multi-phase composites in both 2D and 3D, (ii) development of a new in-house loading rig to support in-situ X-ray CT tests, (iii) reconstruction of low phase-contrast X-ray CT datasets of carbon fibre composites, (iv) integration of X-ray CT image-based models into detailed crack propagation FE modelling and (v) validation of a partially informed multiscale stochastic modelling method by direct comparison with in-situ X-ray CT tensile test results.

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Capillary trapping plays a central role in the geological storage of CO2, oil recovery, and water soil infiltration. The key aim of this study is to investigate the impact of surface properties (wettability, roughness, heterogeneous mineral composition) on the dynamics of quasi-static fluid displacement process and capillary trapping efficiency in porous medium. We concluded that for homogeneous wet smooth glass beads surfaces, a transition in fluid displacement pattern occurs from a compact (for θ < 90°; imbibition process) to a fractal front-pattern (for θ > 90°; drainage process) leading to a crossover in capillary trapping efficiency from zero to maximum. The impact of surface roughness on capillary trapping efficiency was also studied, and an opposite trends in terms of wettability dependency was observed. Rough natural sands surfaces depicts a non-monotonous wettability dependency, i.e. a transition from maximal trapping (for θ < 90°) to no-trapping occurs (at θ = 90°), followed by an increase to medium trapping (for θ > 90°). For a fractional-wet media, the percolating cluster of hydrophobic sediments (connected hydrophobic pathways) characterize the fluid displacement pattern and trapping efficiency.