Dissertations / Theses on the topic 'X-Ray Micro-CT (Micro-Tomography)'

High-resolution micro computed tomography (micro-CT) offers 3D image resolution of 1 um for non-destructive evaluation of various samples. However, the micro-CT performance is limited by several factors. Primarily, scan time is extremely long, and sample dimension is restricted by the x-ray beam and the detector size. The latter is the cause for the well-known interior problem. Recent advancement in image reconstruction, spurred by the advent of compressed sensing (CS) theory in 2006 and interior tomography theory since 2007, offers great reduction in the number of views and an increment in the volume of samples, while maintaining reconstruction accuracy. Yet, for a number of reasons, traditional filtered back-projection based reconstruction methods remain the de facto standard on all manufactured scanners. This work demonstrates that CS based global and interior reconstruction methods can enhance the imaging capability of micro-CT scanners. First, CS based few-view reconstruction methods have been developed for use with data from a real micro-CT scanner. By achieving high quality few-view reconstruction, the new approach is able to reduce micro-CT scan time to up to 1/8th of the time required by the conventional protocol. Next, two new reconstruction techniques have been developed that allow accurate interior reconstruction using just a limited number of global scout views as additional information. The techniques represent a significant progress relative to the previous methods that assume a fully sampled global scan. Of the two methods, the second method uses CS techniques and does not place any restrictions on scanning geometry. Finally, analytic and iterative reconstruction methods have been developed for enlargement of the field of view for the interior scan with a small detector. The idea is that truncated projections are acquired in an offset detector geometry, and the reconstruction procedure is performed through the use of a weighting function / weighted iteration updates, and projection completion. The CS based reconstruction yields the highest image quality in the numerical simulation. Yet, some limitations of the CS based techniques are observed in case of real data with various imperfect properties. In all the studies, physical micro-CT phantoms have been designed and utilized for performance analysis. Also, important guidelines are suggested for future improvements.
Ph. D.

The knowledge of the microstructural properties of cement-based materials plays a fundamental role in predicting their macroscopic behaviour in terms of performance and durability. However, due to the intrinsic microstructural and chemical complexity of such materials, a multi-disciplinary approach is often required. Most classical experimental techniques such as XRD, XRF or mercury porosimetry (MIP) only provide overall information about selected properties (phase and chemical composition, porosity, etc.) but give no indications about their real spatial distribution within the investigated sample. Over the past decades, modern experimental methods for microstructural analysis such as SEM imaging have lead to great advances in our understanding of the complex mechanisms occurring during cement hydration. However, the lack of access to three-dimensional (3D) information represents the main limitation of SEM and other 2D imaging techniques. Furthermore, as sample preparation is often quite invasive, the microstructure of cement may result completely altered. For such reasons, the development of non-destructive techniques for the 3D microstructural investigation of materials has become necessary. Nowadays X-ray computed micro-tomography (X-μCT) provides a totally non-invasive tool to investigate in a three-dimensional way the inner structure of materials, with a spatial resolution reaching the sub-μm level when the most advanced systems are employed. X-μCT allows to reconstruct 3D maps of the variations of the X-ray linear attenuation coefficient (μ) within a sample without perturbing its structure. The aim of this research project is to assess the potential of X-μCT for the microstructural study of several features of interest in cementitious materials. The evolution of the microstructure during setting and hardening, the effects of water-cement ratio (w/c), the role of superplasticizers and the pore space properties are among the major topics that have been investigated. The results obtained from X-μCT at the microscopic scale can then be correlated with the corresponding macroscopic properties observed in real applications. In order to compare the capabilities of the two most common types of X-μCT setups, experiments were carried out using both conventional laboratory instruments and synchrotron-based systems. A synchrotron study of cement evolution during the early hydration stages was successfully performed, focusing the attention on the effect of superplasticizers (chapter 4). The high spatial resolution achievable allowed to follow the evolution of porosity and anhydrous cement fraction as a function of hydration time. In chapter 5, conventional laboratory X-μCT was applied to the study of cement paste samples prepared at different w/c ratios in order to get insights on the microstructural features that determine the variations of strengths in macroscopic samples with varying water contents (chapter 5). In addition, the capabilities of a novel experimental technique (diffraction tomography, XRD-CT) were tested for the first time on cementitious samples (chapter 6). By combining the principles of X-ray micro-diffraction with those of tomographic reconstruction, XRD-CT allows to map the distribution of selected crystalline or amorphous phases within a sample in a totally non invasive manner. In this way, one of the main limitations of X-μCT, related to the poor sensitivity to small absorption variations between different phases can be overcome. Despite the fact that data analysis is not straightforward and requires further developments, the preliminary results presented in this thesis show that crystalline and amorphous phases growing during cement hydration such as ettringite and C-S-H can be successfully mapped without perturbing the system. In the last part of the thesis (chapter 7), a practical application example of X-μCT is reported. The tomographic technique was employed to characterize the pore space properties and the microstructure of cementitious granular materials produced from the solidification and stabilization process (S/S) of soils contaminated by heavy metals. The results of X-μCT analyses were then combined with those obtained using other established experimental methods (e.g. MIP, physico-mechanical and leaching tests) in order to evaluate the performances and environmental compatibility of an innovative method of contaminated grounds remediation.
La conoscenza delle proprietà microstrutturali dei materiali cementizi gioca un ruolo fondamentale nel predire il loro comportamento macroscopico in termini di prestazioni e durabilità. Tuttavia, a causa dell’intrinseca complessità microstrutturale e chimica di tali materiali, un approccio multi disciplinare è spesso richiesto. La maggior parte delle tecniche sperimentali classiche come XRD, XRF o la porosimetria a mercurio (MIP) forniscono solamente informazioni complessive riguardo determinate proprietà (composizione mineralogica e chimica, porosità, etc.) ma non danno alcuna indicazione sulla loro reale distribuzione spaziale all’interno del campione studiato. Nel corso degli ultimi decenni, i moderni metodi sperimentali per l’analisi microstrutturale come la microscopia elettronica a scansione (SEM) hanno portato ad importanti avanzamenti delle nostre conoscenze sui complessi meccanismi che avvengono nel corso dell’idratazione del cemento. Tuttavia, l’impossibilità di accedere ad informazioni tridimensionali (3D) rappresenta la principale limitazione della tecnica SEM e degli altri metodi di imaging 2D. Inoltre, poiché la preparazione del campione è spesso piuttosto invasiva, la microstruttura del cemento può risultare completamente alterata. Per tali ragioni, si è reso necessario lo sviluppo di tecniche non distruttive per lo studio microstrutturale in 3D dei materiali. Oggigiorno, la micro-tomografia computerizzata a raggi X (X-μCT) fornisce uno strumento totalmente non invasivo per studiare in modo tridimensionale la struttura interna dei materiali, con una risoluzione spaziale che può raggiungere il livello sub-micrometrico quando vengono utilizzati i sistemi più avanzati. La X-μCT consente di ricostruire mappe in 3D delle variazioni del coefficiente di attenuazione lineare dei raggi X (μ) all’interno di un campione senza perturbarne la struttura. Lo scopo di questo progetto di ricerca è quello di verificare le potenzialità della X-μCT per lo studio microstrutturale di diversi aspetti di interesse nei materiali cementizi. Tra le principali tematiche che sono state affrontate vi sono l’evoluzione della microstruttura durante la presa e l’indurimento, gli effetti del rapporto acqua-cemento, il ruolo degli additivi superfluidificanti e le proprietà dello spazio poroso. I risultati ottenuti dalla X-μCT alla scala microscopica possono essere correlati con le corrispondenti proprietà microscopiche osservate nelle applicazioni reali. Al fine di confrontare le potenzialità delle due principali tipologie di strumenti per X-μCT, sono stati effettuati esperimenti utilizzando sia sistemi convenzionali da laboratorio sia sistemi da sincrotrone. Uno studio al sincrotrone sull’evoluzione del cemento nel corso degli stadi iniziali dell’idratazione è stato portato a termine con successo, ponendo l’attenzione sull’effetto dei superfluidificanti (cap. 4). L’elevata risoluzione spaziale ottenibile ha consentito di seguire l’evoluzione della porosità e della frazione di cemento anidro in funzione del tempo di idratazione. Nel capitolo 5, la X-μCT convenzionale da laboratorio è stata applicata allo studio di campioni di paste di cemento preparati a diverso rapporto acqua-cemento al fine di ottenere indicazioni sui parametri microstrutturali che determinano le variazioni delle resistenze meccaniche in campioni macroscopici al variare del contenuto d’acqua. Inoltre, le potenzialità di una tecnica sperimentale recentemente sviluppata (diffraction tomography, XRD-CT) sono state testate per la prima volta su campioni cementizi (cap. 6). La tecnica della XRD-CT, combinando i principi della micro-diffrazione a raggi X con quelli della ricostruzione tomografica, consente di mappare la distribuzione di determinate fasi cristalline o amorfe all’interno di un campione in una maniera del tutto non invasiva. In questo modo, una delle principali limitazioni della X-μCT legata alla scarsa sensibilità nei confronti di ridotte variazioni di assorbimento tra diverse fasi può essere superata. Nonostante l’analisi dei dati non sia semplice e richieda ulteriori sviluppi, i risultati preliminari presentati in questa tesi mostrano che alcune fasi, sia cristalline sia amorfe, che si sviluppano nel corso dell’idratazione del cemento (come ad esempio l’ettringite o il C-S-H), possono essere mappate con successo senza perturbare il sistema. Nell’ultima parte del lavoro è riportato un esempio pratico di applicazione della X-μCT. La tecnica tomografica è stata utilizzata per caratterizzare la porosità e la microstruttura di materiali cementizi granulari prodotti dal processo di solidificazione e stabilizzazione (S/S) di suoli contaminati da metalli pesanti. I risultati delle analisi di X-μCT sono stati poi combinati con quelli ottenuti usando altri metodi sperimentali classici (ad esempio MIP, test fisico-meccanici e di cessione) al fine di valutare le prestazioni e la compatibilità ambientale di un metodo innovativo di bonifica dei terreni inquinati.

This master thesis evaluated the performance of a micro-CT system consisting of Hamamatsu microfocus X-ray source L10951-04 and CMOS flat panel C7942CA-22. The X-ray source and flat panel have been characterised in terms of dark current, image noise and beam profile. Additionally, the micro-CT system’s spatial resolution, detector lag and detector X-ray response have been measured. Guidance for full image correction and methods for characterisation and performance test of the X-ray source and detector is presented. A spatial resolution of 7 lp/mm at 10 % MTF was measured. A detector lag of 0.3 % was observed after ten minutes of radiation exposure. The performance of the micro-CT system was found to be sufficient for high resolution X-ray imaging. However, the detector lag effect is strong enough to reduce image quality during subsequent image acquisition and must either be avoided or corrected for.

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.

The understanding of multiphase flow properties is essential for the exploitation of hydrocarbon reserves in a reservoir; these properties in turn are dependent on the geometric properties and connectivity of the pore space. The determination of the pore size distribution in carbonate reservoirs remains challenging; carbonates exhibit complex pore structures comprising length scales from nanometers to several centimeters. A major challenge to the accurate evaluation of these reservoirs is accounting for pore scale heterogeneity on multiple scales. This is the topic of this thesis. Conventionally, this micron scale information is achieved either by building stochastic models using 2D images or by combining log and laboratory data to classify pore types and their behaviour. None of these capture the true 3D connectivity vital for flow characterisation. We present here an approach to build realistic 3D network models across a range of scales to improve property estimation through employment of X-ray micro-Computed Tomography (μCT) and Focussed Ion Beam Tomography (FIBT). The submicron, or microporous, regions are delineated through a differential imaging technique undertaken on x-ray CT providing a qualitative description of microporosity. Various 3-Phase segmentation methods are then applied for quantitative characterisation of those regions utilising the attenuation coefficient values from the 3D tomographic images. X-ray micro-CT is resolution limited and can not resolve the detailed geometrical features of the submicron pores. FIB tomography is used to image the 3D pore structure of submicron pores down to a scale of tens of nanometers. We describe the experimental development and subsequent image processing including issues and difficulties resolved at various stages. The developed methodology is implemented on cores from producing wackstone and grainstone reservoirs. Pore network models are generated to characterise the 3D interconnectivity of pores. We perform the simulations of petrophysical properties (permeability and formation resistivity) directly on the submicron scale image data. Simulated drainage capillary pressure curves are matched with the experimental data. We also present some preliminary results for the integration of multiscale pore information to build dual-scale network models. The integration of multiscale data allows one to select appropriate effective medium theories to incorporate sub-micron structure into property calculations at macro scale giving a more realistic estimation of properties.

Diplomová práce se zabývá detektory rentgenového záření pro mikro-CT systémy. Teoretická část zahrnuje standartní typy rentgenových detektorů a požadavky na kvalitu obrazu pro výslednou 3D rekonstrukci. V závěru jsou popsány fyzikální parametry reálných detektorů a metody jejich měření a vyhodnocení.

The characterization of the normal pulmonary acinus is a necessary first step in understanding the nature of respiratory physiology and in assessing the etiology of pulmonary pathology. Murine models play a vital role in the advancement of current understanding of the dynamics of gas exchange, particle deposition and the manifestations of diseases such as COPD, Cystic Fibrosis and Asthma. With the advent of interior tomography techniques, high-resolution micro computed tomography (μCT) systems provide the ability to nondestructively assess the pulmonary acinus at micron and sub-micron resolutions. With the application of Systematic Uniform Random Sampling (SURS) principles applied to in-situ fixed, intact, ex-vivo lungs, we seek to characterize the structure of pulmonary acini in mice and study the variations across dimensions of age, location within the lung and strain phenotypes. Lungs from mice of three common research strains were perfusion fixed in-situ, and imaged using a multi-resolution μCT system (Micro XCT 400, Zeiss Inc.). Using lower resolution whole lung images, SURS methods were used for identification of region-specific acini for high-resolution imaging. Acinar morphometric metrics included diameters, lengths and branching angles for each alveolar duct and total path lengths from entrance of the acinus to the terminal alveolar sacs. In addition, other metrics such as acinar volume, alveolar surface area and surface area/volume ratios were assessed. A generation-based analysis demonstrated significant differences in acinar morphometry across young and old age groups and across the three strains. The method was successfully adapted to large animals and the data from one porcine specimen has been presented. The registration framework provides a direct technique to assess acinar deformations and provides critical physiological information about the state of alveolar ducts and individual alveoli at different phases of respiration. The techniques presented here allow us to perform direct assessment of the three-dimensional structure of the pulmonary acinus in previously unavailable detail and present a unique technique for comprehensive quantitative analysis. The acinar morphometric parameters will help develop improved mathematical and near-anatomical models that can accurately represent the geometric structure of acini, leading to improved assessment of flow dynamics in the normal lung.

Cette thèse présente une étude expérimentale pour améliorer le moulage par compression et transfert de résine thermoplastique (CRTM), axée sur l'efficacité industrielle, la durabilité et la recyclabilité, conformément aux objectifs de développement durable pour l’industrie, l’innovation et l’action climatique. En abordant la complexité de l'écoulement de la résine à plusieurs échelles dans le CRTM, cette recherche étudie l'écoulement transversal (à travers l’épaisseur) et la porosité induite par le processus à l'échelle méso des faisceaux de fibres de verre afin d'améliorer l'uniformité de l'imprégnation et le contrôle du compactage, en faisant le lien entre les cadres théoriques et les applications évolutives. L’étude est conduite sur une préforme, constituées de 6 couches de fibres de verre UD ([0/90]3) et d’une matrice thermoplastique en polypropylene (PP) mise en forme par un procédé CRTM . Un procédé « CRTM simplifié » permettant de contrôler la direction du front de matière est développé sur une presse industrielle, pilotée en déplacement. Trois configurations de procédé sont analysées : Configuration 1 (Référence) : configuration de type « film stacking » comme base de comparaison de la distribution de la résine et de la structure des fibres. Configuration 2 (CRTM simplifié) : Compression contrôlée par déplacement, les films de polymères formant initialement une couche unique en surface de la préforme. Configuration 3 (CRTM simplifié avec scellement des bords) : Compression améliorée avec un dispositif d’étanchéité limitant les fuites de résine en périphérie de la préforme et assurant un écoulement transversal. Un protocole d’analyse d'imagerie 2D est proposé, incluant l’analyse en lumière polarisée, la microscopie à fluorescence et la microscopie électronique à balayage pour caractériser qualitativement et quantitativement les taux de porosités au niveau des mèches et des plis de tissus. Un processus original de polissage en deux étapes permet de préserver l'intégrité de la surface. L'étude est complétée par une évaluation fine des mécanismes d'imprégnation à l'aide de la technique d'inspection hélicoïdale en microtomographie à rayon-X (micro-CT). Les résultats démontrent que les paramètres de compaction influencent directement le niveau d'imprégnation, atteignant une limite d'imprégnation. Cette thèse établit une démarche d’analyse du procédé CRTM pour des composites thermoplastiques haute performance, en vue d’une maitrise et d’une optimisation du procédé. Elle offre des perspectives sur des protocoles d’analyse précis basés sur l’étude à différentes échelles, améliorant la compréhension de l'interaction entre l'imprégnation et la perméabilité. Ces résultats répondent aux exigences de précision dans des secteurs tels que l'automobile et l'aérospatiale, où les composites CRTM sont essentiels pour les applications structurelles
This thesis presents an experimental study to advance thermoplastic Compression Resin Transfer Molding (CRTM), focusing on industrial efficiency, sustainability, and recyclability goals aligned with the Sustainable Development Goals for Industry, Innovation, and Climate Action. By addressing multi-scale resin flow complexity in CRTM, this research investigates transverse flow and process-induced porosity at the meso scale of glass fiber bundles to improve impregnation uniformity and compaction control, bridging theoretical frameworks with scalable applications. The study focuses on a thermoplastic polypropylene matrix reinforced with six layers of bidirectional UD woven glass fibers ([0/90]3) consolidated on a CRTM setup. The “Simplified CRTM” method is developed on an industrial press, using displacement-controlled compaction ratios. This method omits active resin injection, relying on a uniformly distributed viscous polymer pool beneath the unsaturated preform to drive resin flow uniformly with a unidirectional flow path. Controlled displacement and pressure optimize resin paths, manage fiber volume fraction, and reduce porosity. Three multi-step compaction configurations are evaluated: Configuration 1 (Reference): Uses force compaction as a baseline for comparing resin distribution and fiber structure. Configuration 2 (simplified CRTM): Displacement-controlled compaction enhances resin infiltration but faces challenges like edge race-tracking and fiber volume fraction (Vf) variability, affecting impregnation. Configuration 3 (simplified CRTM with Edge Sealing): Introduces high-temperature sealant tape at mold edges, limiting resin escape, maintaining transverse flow, and reducing porosity and race-tracking. Configuration 3 edge-sealing technique establishes a reproducible process for high quality CRTM composites. An advanced 2D multi-modal imaging protocol, tailored for partially impregnated samples produced via simplified CRTM with unfilled spaces and fragile microstructures, includes polarized light microscopy, fluorescence microscopy, and scanning electron microscopy for qualitative and quantitative characterization. An original two-step polishing process preserves surface integrity, and image post-processing workflows quantify impregnation quality and void distribution. The study is completed with a fine evaluation of the impregnation mechanisms using X-ray micro computed tomography technique (micro-CT) relying on helicoidal inspection method. Results demonstrate that compaction parameters directly impact impregnation level, reaching an impregnation limit. This thesis establishes a scalable, data-driven CRTM framework bridging laboratory experimentation with industrial requirements for high-performance thermoplastic composites. It offers insights into streamlined protocols and microstructure-based analysis, enhancing understanding of the interplay between impregnation and permeability in CRTM. These findings align with precision demands in sectors like automotive and aerospace, where CRTM composites are crucial for structural applications

La thèse a pour but d’étudier les effets de changements de mouillabilité de roches dans des conditions d’injections d’eau douce en tant que méthode de récupération d’hydrocarbures. Afin d’identifier le ou les mécanismes à l’origine du gain additionnel de récupération nous avons utilisé un microtomographe RX. Nous avons ainsi imagé les états de saturations finales d’un milieu poreux rempli de saumures et d’huiles. Une fois le drainage primaire réalisé nous avons effectué deux phases d’imbibitions : avec une saumure (récupération secondaire) puis une imbibition d’eau douce (récupération tertiaire). L’analyse de la mouillabilité à l’échelle du pore a permis de mettre en évidence l’effet de la température et de la salinité sur la mouillabilité. Nous avons montré que les changements de mouillages des roches n’étaient pas occasionnées par la seule expansion de la couche électrique en revanche des changements de mouillabilité ont été montrés. Ces changements s’expliquant par des transitions de mouillages de second ordre observées non seulement pour des gouttes d’huiles sur de l’eau mais également sur un substrat en verre. Au final, la mouillabilité en milieux poreux doit être mise en évidence à une échelle sous-Micrométrique ce qui est relativement nouveau dans le domaine pétrolier
The aim of the thesis is to study rock wettability change effects caused by Low Salinity brine injection as tertiary recovery method. To identify the underlying mechanism or mechanisms of additional oil recovery X-Ray imaging technology was applied. We have also imaged the end-Point saturations of filled by brine and water core samples. Once the primary drainage is realized we carried out two phases imbibitions: with high salinity brine (waterflooding) and with low salinity brine (tertiary recovery mode). The wettability analysis at pore scale permitted to put in evidence the thermal and saline effects playing a decisive role in rock wettability. We have showed wettability changes are not caused by only electrical double layer expansion, however wettability changes was shown. These changes are explained by wettability transition of second order and observed not only for oil droplet on brine, but also for oil deposited on glass substrate. Finally, the pore space wettability needs to be evidenced at sub-Micrometric scale that is new for the petroleum domain

Automatická segmentace biologických struktur v mikro-CT datech je stále výzvou, protože často objekt zájmu (v našem případě obličejová chrupavka) není charakterizovaný unikátním jasem či ostrými hranicemi. V posledních letech se konvoluční neuronové sítě (CNNs) staly mimořádně populárními v mnoha oblastech počítačového vidění. Konkrétně pro segmentaci biomedicínských obrazů je široce používaná architektura U-Net. Nicméně v případě mikro-CT dat vyvstává otázka, zda by nebylo výhodnější použít 3D CNN. Diplomová práce navrhla CNN architekturu založenou na síti V-Net včetně metodologie pro předzpracování a postprocessing dat. Základní architektura byla dále optimalizována pomocí pokročilých architektonických modifikací jako jsou pyramidální modul dilatovaných konvolucí (ASPP modul), škálovatelná exponenciálně-lineární jednotka (SELU aktivační funkce), víceúrovňová kontrola učení (multi-output supervision) či bloky s hustými propojeními (Dense blocks). Pro učení sítě byly použity moderní přístupy jako zahřívání kroku učení (learning rate warmup) či AdamW optimalizátor. I přes to, že 3D CNN v úloze segmentace obličejové chrupavky nepřekonala U-Net, optimalizace zvýšila medián Dice koeficientu z 69,74 % na 80,01 %. Používání těchto pokročilých architektonických modifikací v dalším výzkumu je proto vřele doporučováno, jelikož můžou být přidány do libovolné architektury typu U-Net a zároveň výrazně zlepšit výsledky.

X-ray micro computed tomography (CT) is a useful tool for imaging 3-D internal structures. It has many applications in geophysics, biology and materials science. Currently, micro-CT’s capability are limited due to validity of assumptions used in modelling the machines’ physical properties, such as penumbral blurring due to non-point source, and X-ray refraction. Therefore many CT research in algorithms and models are being carried out to overcome these limitations. This thesis presents methods to improve image resolution and noise, and to enable material property estimation of the micro-CT machine developed and in use at the ANU CTLab. This thesis is divided into five chapters as outlined below. The broad background topics of X-ray modelling and CT reconstruction are explored in Chapter 1, as required by later chapters. It describes each X-ray CT component, including the machines used at the ANU CTLab. The mathematical and statistical tools, and electromagnetic physical models are provided and used to characterise the scalar X-ray wave. This scalar wave equation is used to derive the projection operator through matter and free space, and basic reconstruction and phase retrieval algorithms. It quantifies the four types of X-ray interaction with matter for X-ray energy between 1 and 1000 keV, and presents common assumptions used for the modelling of lab based X-ray micro-CT. Chapter 2 is on X-ray source deblurring. The penumbral source blurring for X-ray micro-CT systems are limiting its resolution. This chapter starts with a geometrical framework to model the penumbral source blurring. I have simulated the effect of source blurring, assuming the geometry of the high-cone angle CT system, used at the ANU CTLab. Also, I have developed the Multislice Richardson-Lucy method that overcomes the computational complexity of the conjugate gradient method, while produces less artefacts compared to the standard Richardson-Lucy method. Its performance is demonstrated for both simulated and real experimental data. X-ray refraction, phase contrast and phase retrieval (PR) are investigated in Chapter 3. For weakly attenuating samples, intensity variation due to phase contrast is a significant fraction of the total signal. If phase contrast is incorrectly modelled, the reconstruction would not correctly account the phase contrast, therefore it would contribute to undesirable artefacts in the reconstruction volume. Here I present a novel Linear Iterative multi-energy PR algorithm. It enables material property estimation for the near field submicron X-ray CT system and reduces the noise and artefacts. This PR algorithm expands the validity range in comparison to the single material and data constrained modelling methods. I have also extended this novel PR algorithm to assume a polychromatic incident spectrum for a non-weakly absorbing object. Chapter 4 outlines the space filling X-ray source trajectory and reconstruction, on which I contributed in a minor capacity. This space filling trajectory reconstruction have improved the detector utilisation and reduced nonuniform resolution over the state-of-the-art 3-D Katsevich’s helical reconstruction, this patented work was done in collaboration with FEI Company. Chapter 5 concludes my PhD research work and provides future directions revealed by the present research.

A procedure is presented to analyze select geometric and effective properties of the porous transport layer (PTL) of the polymer electrolyte membrane fuel cell (PEMFC) in com- pressed and uncompressed states using micro-computed X-ray tomography (Micro CT). A method of compression using a novel device design was employed to mimic the non-homogeneous compression conditions found in functioning fuel cells. The process also features open source image processing and CFD analysis through the use of software packages Fiji and OpenFOAM (proprietary software is also used such as Matlab). Tomographic images of a PTL sample in different compressive states are first analyzed by measuring local porosity values in the through-plane and both in- plane directions. The objective of this study was to develop a method for imaging the PTL structure to show directionality within its properties using relatively inexpensive and non-destructional means. Three different PTL types were tested, one without any additives, one with Polytetrafluoroethylene (PTFE) and one with PTFE and a microporous layer (MPL). Non-homogeneous porosity was shown to exist with the highest and least variable porosity values obtained from the in-plane direction that was in-line with the direction of fibres. Porosity values compared well with values obtained from the literature. The profile of the PTL with MPL added was unattainable using this procedure as the resolution of the Micro CT was too low to resolve its pore space. The next stage involved the effective properties analysis which included effective electronic conductivity and effective diffusivity. It was found that the through-plane values for the effective electronic conductivity study were higher than expected. The ratio between through-plane and in-plane was found to be much higher than expected from literature. Lack of sufficient resolution of fibre contacts has been shown to play a role in this discrepancy. These contact problems were shown not too affect measurements of diffusivity in the pore phase. The in-plane direction parallel to the direction of fibres was found to have the highest values of effective transport properties. Effective diffusivity ratios of between 0.1 and 0.37 were found to be reasonable with the limited experimental evidence found in literature. The it was found that the Bruggeman relation for calculating diffusivity and percolation theory by Tomadakis and Sotirchos over predicted the values for diffusion within the PTL and it is suggested that these theories are not suitable for predicting diffusivity for this material.
Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2012-02-02 15:46:29.395

Grow: Experiencing Nature in the Fifth Dimension, is an interdisciplinary practice-led research project traversing the realms of art, science and technology through the exploration of germinating seeds. Through my investigation of the aesthetic possibilities of the computational extension of vision with time-resolved (4D) micro-X-ray Computed Tomography, I have tested the potential for visualising virtual germinating seeds in an immersive stereoscopic installation. Using this technology I have set out to create a work of art where an audience can experience seed growth from a very different perspective. However, the rationale to propagate seeds in this way began not just to test the limitations and possibilities of this technology. As an artistic inquiry, my premise for focusing on plant life also began as a way to examine this work from an ecological perspective. By considering the third and fourth dimensional elements in this project I am proposing that an individual’s experience of nature in my work can be considered as an additional ‘fifth dimension’. My research is placed within a range of disciplines from contemporary art and new media practices to scientific technological research and the natural sciences. The works of art developed through this research have been viewed in relation to ideas of the fourth dimension in modern art, to microscopy in both historical and contemporary art practice, to contemporary installation practices, and in relation to ideas of time and wonder. My experience of meeting the Seed Morphologist Dr Wolfgang Stuppy and staying at the Millennium Seed Bank, Royal Botanic Gardens, West Sussex in the UK has also been a point of reflection. The seed becomes a visual analogy for ideas of time, growth and renewal in the context of issues of creating art in the time of the Anthropocene. This exegesis explores the multi-dimensional properties of my research in the wider context of art, science and philosophy.