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In this paper, a novel approach for tracking moving structures in multiphase flows over larger axial ranges is presented, which at the same time allows imaging the tracked structures and their environment. For this purpose, ultrafast electron beam X-ray computed tomography (UFXCT) is being extended by an image-based position control. Application is scanning and tracking of, for example, bubbles, particles, waves and other features of multiphase flows within vessels and pipes. Therefore, the scanner has to be automatically traversed with the moving structure basing on real-time scanning, image reconstruction and image data processing. In this paper, requirements and different strategies for reliable object tracking in dual image plane imaging mode are discussed. Promising tracking strategies have been numerically implemented and evaluated.

Ce travail de thèse s’est attaché à investiguer, d’une part, le mécanisme d’érosion interne par suffusion dans les ouvrages hydrauliques en terre, et d’autre part, les conséquences qu’il pourrait avoir sur le comportement mécanique du sol, l’objectif principal étant d’améliorer notre compréhension de ce processus et du comportement des sols érodés. La démarche adoptée est principalement expérimentale, réalisée à différentes échelles : du macroscopique, à l’échelle du matériau, au microscopique, à l’échelle des grains constitutifs. A l’échelle macroscopique, des essais de suffusion ont été réalisés sur des échantillons de sol à l’aide d’un nouveau dispositif d’essai d’érosion, appelé perméamètre de suffusion, développé dans le cadre de cette thèse. Après érosion dans le perméamètre, les échantillons érodés sont transférés par une procédure de congélation / décongélation dans un dispositif d’essai triaxial afin d’étudier leur comportement sous chargement mécanique. Les résultats obtenus à cette échelle ont permis de donner un aperçu général du mécanisme de suffusion et de mettre en évidence son impact sur les propriétés de résistance au cisaillement du sol. A l’échelle microscopique, une analyse fine a pu être menée en réalisant un essai de suffusion des mesures in-operando de tomographie à rayons X et de la visualisation locale par techniques optiques sur un sol artificiel. La caractérisation du sol à cette échelle microstructurale a permis de mieux comprendre le processus de suffusion, notamment en mettant en évidence l’apparition et le développement de fortes hétérogénéités qui semblent avoir une influence importante sur la réponse mécanique des sols érodés / This thesis work has investigated, on the one hand, the mechanism of internal erosion by suffusion in earthen hydraulic structures, and, on the other hand, the consequences suffusion can cause on the mechanical behavior of soils, the main objective being to improve our understanding of both the suffusion process and the behavior of eroded soils. The approach adopted was mainly experimental, by a multi-scale scope: from macroscopic, at the material scale, to microscopic, at the grain scale. At the macroscopic scale, suffusion experiments were performed on gap-graded cohesionless soil samples using a newly developed testing device, called the suffusion permeameter. Then, the eroded samples are transferred by a freeze/thaw procedure to a triaxial device to study their behavior under mechanical loading. The achieved results provide a general overview of the suffusion mechanism at the sample scale and highlight its impact on soil shear resistance properties. At the microscopic scale, the suffusion mechanism has been studied by performing a suffusion test with in-operando x-ray tomography and using local visualization based on optical techniques in an artificial soil. Subsequent grain-scale analysis has provided a deeper understanding of suffusion process through the characterization of the eroded soil microstructure, particularly highlighting the occurrence and development of strong heterogeneities, which appear to play a key role in the macroscopic mechanical behavior of eroded soils

Ce mémoire a pour objectif de mieux comprendre la tomodensitométrie par rayons-x appliquée à la géocryologie. La majorité des études ayant pour but d’analyser le pergélisol en utilisant la tomodensitométrie sont qualitative. De ce fait, il est principalement question de décrire les cryostructures et la disposition géométrique de la glace dans le pergélisol. Il existe peu d’études quantitatives où le volume de glace est estimé avec la tomodensitométrie. De ce fait les méthodologies quantitatives sont peu développées et leur degré de confiance est mal connu. Des échantillons de pergélisol ont été scannés puis analysés avec le logiciel de visualisation Dragonfly©. Une méthode d’analyse quantitative a été développée et combinée à des mesures en laboratoire afin de déterminer l’erreur entre la proportion en glace estimée sur les Ct-Scans et celle mesurée sur l’échantillon physique. Ensuite, une équation pour essayer de corriger cette erreur a été appliquée. Celle-ci a été déterminée à partir de comparaisons des estimations des volumes de glace sur les Ct-Scans et leurs valeurs mesurées en laboratoire. Ces comparaisons ont également permis d’estimer la quantité de matière organique présente dans un échantillon. Les cryostructures du pergélisol ont été modélisées en 3D. Cela a permis de bonifier la classification Nord-Américaine établie par Murton et French en 1994 et de quantifier les volumes respectifs de glace et de sédiments. / This thesis aims to better understand x-ray computed tomography in geosciences and more particularly its use with frozen ground science. Most studies in permafrost science using x-ray computed tomography were qualitative. Therefore, they mainly describe the permafrost cryostructures and the geometric arrangement of the ice in permafrost. There were few quantitative studies where the volumetric ice content of permafrost was estimated with Ct-Scans. As a result, quantitative methodologies are poorly developed, and their degree of confidence is also poorly assessed. Samples from different locations in the Canadian Arctic were scanned and analyzed using Dragonfly©, a visualization software. A quantitative analysis method has been developed and combined with laboratory measurements to calculate the error between the proportion of ice estimated on the Ct-Scans and the one measured on the physical sample. A correction method was developed and applied to the Ct-scans dataset to reduce the error in volumetric ice content estimations. This equation also allows to give an estimation of the organic matter proportion inside a sample. The permafrost cryostructures were modeled in 3D. This improved the visualization of the cryostructures of the North American classification established by Murton and French in 1994, and it allowed to quantify their volumetric ice and sediment contents.

This dissertation presents a comprehensive investigation into the mechanical properties of fiber-reinforced concrete (FRC), focusing on fracture and flexural toughness properties, the impact of fiber orientation and distribution, and the evaluation of flexural models for predicting the behavior of functionally graded FRC. It embarks on a critical investigation aimed at bridging a significant gap in the understanding of FRC materials' behavior, particularly in terms of fracture and flexural performance. Across five distinct manuscripts, this work employs a variety of experimental methodologies, including three-point bend tests, four-point bend tests, digital image correlation, X-ray computed tomography, and the implementation of the two parameter fracture model and then size effect fracture method to explore the effects of different casting techniques – namely, conventional casting and pump-driven extrusion – on the performance of FRC. The core hypothesis tested throughout these studies suggests that the extrusion process, by aligning fibers parallel to tensile stresses, significantly enhances the concrete's ductility, post-peak behavior, and overall fracture and flexural properties. This hypothesis was corroborated across various experiments, which demonstrated that fiber alignment via extrusion not only enhances the concrete's mechanical properties but also leads to more effective crack propagation control, increased toughness, and enhanced residual strengths. The research encompasses a series of systematic investigations into the effects of fiber alignment on the mechanical properties of FRC, revealing that the extrusion process significantly enhances fracture and flexural properties and maintains residual strength after peak stress. Utilizing both extrusion-based and conventional casting methods with varying dosages of polyvinyl alcohol fibers, the study demonstrates notable improvements in fracture properties, deflection at failure, and equivalent flexural strength ratio for extrusion-based specimens compared to their conventionally cast counterparts. Moreover, the dissertation explores the impact of casting methods and fiber orientation on fracture energy, offering a size-dependent improvement in extrusion-based methods. The strategic distribution of steel fibers, employing an innovative targeted fiber injection for creating Functionally Graded FRC (FG-FRC), is shown to significantly enhance the structural integrity and resilience of the material. The analysis of flexural models applied to FG-FRC specimens, proposing a novel functionally graded factor to improve model predictability, further advances the understanding of the predictability and reliability of these models in assessing FRC's structural behavior. This dissertation advances academic knowledge in the field of FRC casting and offers significant implications for the construction industry, demonstrating a profound understanding of the challenges and opportunities in extrusion-based FRC casting. Through its innovative approach and detailed investigations, this work contributes significantly to the advancement of the FRC casting field, paving the way for the development of more resilient and efficient construction materials. / Doctor of Philosophy / This research explores the enhancement of concrete's strength and flexibility through the incorporation of individual fibers, with a special focus on the integration and alignment of these fibers. The study examines how concrete can be made more resilient by mixing in fibers in specific ways. A variety of tests, including bending beams and employing advanced imaging techniques, were conducted to observe the effects of mixing fibers using traditional methods versus a novel extrusion-based technique that aligns the fibers in the desired direction in the concrete. The research hypothesized that this innovative alignment method would improve the concrete's ductility and enhance its ability to resist crack propagation. The findings confirmed this hypothesis, revealing that aligned fibers significantly improve concrete's bending capacity, reduce sensitivity to cracking, and retain residual strength even after cracking. Further investigation into varying methods of fiber addition, such as a targeted approach for placing fibers in strategic locations, demonstrated a marked enhancement in the material's ductility. Additionally, the study evaluated mathematical models for predicting the behavior of fiber-reinforced concrete, aiming to improve the understanding and reliability of these models for practical construction applications. In short, the research underscores that adjusting the method of fiber integration into concrete can lead to the development of structures that are both stronger and more durable. This advancement holds promising implications for the future of construction, offering pathways to create more resilient and efficient building materials.

Concrete is the most widely used construction material in the world. Given its relative availability, strength, economy, and versatility to fit various applications, the material has been incorporated in roadways, bridges, buildings, and a host of other infrastructure projects. Oftentimes, concrete will be exposed to several environmental conditions that ultimately affect its durability and lifespan. These conditions include repeated freezing and thawing, chloride intrusion, sulfate attack, alkali-silica reaction, and many others. Given the age and condition of American infrastructure, concrete structures throughout the country need repair or rehabilitation. Often this repair includes the removal of degraded or damaged concrete and the application of an overlay material. There are several factors affecting the bond performance of the newly formed substrate-repair concrete, such as surface roughness, overlay material, and substrate moisture condition. The work presented in this thesis is dedicated to understanding the effect of substrate moisture condition on the overlay transition zone (OTZ) of the substrate-repair concrete. The substrate moisture condition can significantly impact the microstructure characterization of the OTZ. If the substrate is too dry, then it may absorb water from the repair material, reducing the local water-to-cement (w/c) ratio in the OTZ. Conversely, if the substrate is too wet, then the w/c ratio of the OTZ will be locally increased. In both scenarios, the interfacial bond strength is expected to be modified due to the change in the local w/c ratio. To understand this effect, various test methods and degradation mechanisms were explored. Initially, substrate-repair concrete specimens were prepared utilizing three separate substrate moisture conditions: saturated surfaced dry (SSD), sub-saturated surface dry (Sub-SSD), and oven dry (OD). After allowing these samples to cure, the strength and ion penetration risk were evaluated. The bond strength of the samples was evaluated through flexural strength testing and fracture energy determined through the RILEM draft tests. The OTZ ion penetration risk was evaluated by conducting rapid chloride penetration test (RCPT) on samples prepared with the three substrate moisture conditions. Furthermore, to determine the effect of repeated freezing and thawing on the OTZ and flexural strength, additional samples were created with the three moisture conditions. After allowing these samples to cure, they were subjected to ASTM C666 and were tested to observe their flexural strength. Another important performance indicator of concrete elements is its resistance to chloride ion penetration and corrosion. Since many structural elements are designed with steel reinforcement, chloride ion penetration represents a critical parameter in projecting material performance, since chloride ions will accelerate the rate of steel corrosion. Oftentimes, a key element in projecting this performance is identifying the rate at which ions diffuse through the material. There remain many established techniques to identify this rate of diffusion and derive a chloride diffusion coefficient; however, many of them are either destructive or qualitative in nature. In recent years, transmission X-ray microscopy (TXM) has been employed to non-destructively track diffusion and develop diffusion coefficients. The work presented in this thesis surrounds the efforts of incorporating TXM experiments at Virginia Tech. This work initially utilized a SkyScan 1174 μCT, and additional work in this thesis presents the design and construction of a dental X-ray system based on the checking ion penetration (CHIP) design. This system can conduct TXM experiments utilizing a dental X-ray as the source. The research, design, and construction of the CHIP system is discussed in this thesis. Ultimately, the research in this thesis has not observed any significant relationship between substrate moisture condition and overlay bond strength. There does appear to be an increase in chloride ion resistance for drier substrates, suggesting that pre-wetting the surface increases penetrability of the interface. / Master of Science / Concrete is the most widely used construction material in the world. Given its relative availability, strength, economy, and versatility to fit various applications, the material has been incorporated in roadways, bridges, buildings, and a host of other infrastructure projects. Oftentimes, concrete will be exposed to several environmental conditions that ultimately affect its durability and lifespan. These conditions include repeated freezing and thawing, chloride intrusion, sulfate attack, alkali-silica reaction, and many others. These environmental conditions ultimately degrade the material by inducing cracks, exposing steel reinforcement, and spalling. When the concrete has experienced significant deterioration, repair and rehabilitation of the damaged section must be performed. Most often, this repair consists of the removal of damaged concrete and the application of an overlay material to prevent further deterioration. The topics discussed in this thesis evaluate the optimum substrate conditions prior to an overlay application and the implementation of techniques to evaluate deterioration mechanisms. There are several substrate conditions that will affect bonding with the overlay material, including surface roughness, moisture conditions, and overlay type. This paper focused on the moisture condition and what effect this had on bond strength and resistance to chloride intrusion. This effect was studied in laboratory conditions and under environmental conditions such as rapid freezing and thawing. Several different deterioration mechanisms may contribute to concrete degradation. The research presented in this thesis also aimed to evaluate chloride ion diffusion. To evaluate this mechanism, two systems were explored with the intent of conducting transmission X-ray microscopy (TXM). With TXM, chloride ion diffusion can be tracked to determine the rate at which ions diffuse through the concrete. The two systems explored were an X-ray computed tomography scanner and a dental X-ray system. Both systems can conduct TXM, and this paper presents the efforts dedicated to developing them for this technique at Virginia Tech. Ultimately, the research in this thesis has not observed any significant relationship between substrate moisture condition and overlay bond strength. There does appear to be an increase in chloride ion resistance for drier substrates, suggesting that pre-wetting the surface increases penetrability of the interface.

Unconventional gas reservoirs in carbon dioxide sequestration activities is a relatively new and unexplored concept currently undergoing pilot scale testing. Sequestration has the potential for enhancing gas recovery while mitigating carbon dioxide to long term storage structures. Due to the extremely complex systems associated with these unconventional reservoirs, modeling becomes difficult to predict accurately. This thesis presents methods to increase the confidence of inferred parameter testing for unconventional reservoir sequestration in both seam coal bed methane wells and a shale wells. Various tests include the use of computed tomography coupled with Avizo modeling software, inductively coupled mass spectrometer fluid transport analysis, pressure transient build tests, liquid level detection, and desorption analysis coupled with cleat image analysis. Analyses of coals performed by both environmental scanning electron microscope (ESEM) and micro CT demonstrate that distributions of cleat porosity in coals are anisotropic and not correlated to the seam depth or location. ESEM is used with micro CT scanning to verify the results before and after the impregnation of the carbonic acid. The micro CT data in Avizo Fire© was used calculate an increase in cleat permeability by 25%. The increase of major flow pathways is caused by the dissolution of carbonates. Changes in the structures were observed qualitatively through ESEM and micro CT and quantitatively through Avizo and inductively coupled mass spectrometry. The results of comparative study between the cleat structures and the desorption of various seams indicate a trend in the cleat porosity and the desorption rate of the coals as well as the cleat porosity and the total gas in various seams. / Master of Science

Du fait de leurs propriétés physiques et chimiques exceptionnelles à haute température par rapport aux métaux, les composites de carbure de silicium (SiC) sont étudiés comme éventuel matériau de gainage du combustible nucléaire dans les réacteurs de fusion ou fission avancée futurs, ainsi que, depuis plus récemment, dans les réacteurs à eau légère existants. Les tubes composites SiC/SiC tressés en 2D, fabriqués par procédé d'infiltration chimique en phase vapeur (CVI), présentent un comportement mécanique anisotrope, faiblement déformable (~ 1%). La maîtrise des relations entre la microstructure, l’endommagement et le comportement macroscopique est essentielle pour optimiser précisément le dimensionnement structurel de ce matériau pour les applications envisagées. Un paramètre de fabrication important est l'angle de tressage, angle entre les torons de fibres et l'axe du tube. L'objectif de ce travail est de fournir une compréhension détaillée de la relation endommagement-microstructure, en particulier des effets de l'angle de tressage sur les mécanismes d’endommagement. Dans ce but, une étude combinant observations expérimentales à macro et micro-échelle et simulations numériques est menée. Les tubes composites sont d’abord étudiés par des essais de traction in situ sous tomographie par rayons X. Les expériences ont été réalisées sur la ligne PSICHE du synchrotron SOLEIL sous faisceau rose polychromatique. Les images tridimensionnelles sont analysées par la technique de corrélation d’image volumique (DVC), complétée par une série d'algorithmes de traitement d'image originaux, développés spécifiquement pour analyser les microstructures 3D, mesurer les déformations à travers l'épaisseur du tube, détecter et caractériser quantitativement le réseau de microfissures créées par le chargement mécanique. De plus, les microstructures réelles, décrites par les images de haute résolution issues des tests in situ, sont utilisées dans les simulations numériques multi-échelle. Les champs de contrainte à l’échelle microstructurale sont calculés en régime élastique par une technique utilisant la transformée de Fourier rapide (FFT). Ils permettent de mieux comprendre l'initiation des fissures et d’interpréter les observations expérimentales par une comparaison directe. Ces approches expérimentales et numériques sont appliquées à trois tubes présentant différents angles de tressage (30 °, 45 ° et 60 °). L’influence de l'angle de tressage sur l'initiation et l'évolution de l’endommagement à cœur des composites est ainsi mise en évidence / Because of their outstanding physical and chemical properties at high temperature, in comparison with metals, silicon carbide (SiC) composite materials are studied as possible nuclear fuel cladding materials either for future advanced fission/fusion reactors, or more recently, for the currently existing light water reactors. 2D-braided SiC/SiC composite tubes, manufactured by chemical vapor infiltration (CVI), exhibit an anisotropic, hardly deformable (~1%) mechanical behavior. Understanding the relations between the microstructure, the damage mechanisms and the macroscopic behavior is essential to optimize the structural design of this material for the considered applications. One important manufacturing parameter is the braiding angle, i.e. the angle between the fiber tows and the tube axis. The objective of this work is to provide a comprehensive understanding of the damage-microstructure relations, in particular of the effects of the braiding angle on the damage mechanisms. For this purpose, an investigation combining experimental observations at macro and micro-scale and numerical simulations is developed. The composite tubes are first studied through in situ tensile testing under X-ray computed tomography. Experiments were carried out on the PSICHE beamline at synchrotron SOLEIL using a pink polychromatic beam. The recorded 3D images are processed using the digital volume correlation (DVC) technique, extended by a series of advanced image processing algorithms specifically developed in order to analyze the 3D microstructures, to measure the deformations through the tube thickness, and to detect and quantitatively characterize the network of micro-cracks created by the mechanical loading. In addition, numerical simulations are performed on the real microstructures as observed in the high-resolution images recorded during the in situ tests. Stress fields are calculated at the microstructural scale in the elastic regime using a numerical tool based on the Fast Fourier Transform (FFT). They help to better understand crack initiation and interpret the experimental observations within one-to-one comparisons. Both the experimental and numerical approaches are applied to three tubes with different braiding angles (30°, 45° and 60°). The effect of the braiding angle on the initiation and evolution of damage in the bulk of the composite materials can thus be highlighted

Introdução: O aumento alarmante da obesidade em todo mundo é um fator independente para o aumento da prevalência de doenças crônicas, como diabetes, hipertensão arterial e doença hepática gordurosa não alcoólica (DHGNA). A DHGNA engloba um amplo espectro de doença desde esteatose simples sem sinais inflamatórios, evoluindo para esteatohepatite (ENA) e até cirrose. Por ser uma patologia multifatorial sua patogênese e terapêutica ainda apresentam pontos obscuros. A resistência à insulina é um dos fatores que já foram determinados como importantes na fisiopatogênese da DHGNA e, está diretamente relacionado ao estilo de vida e hábitos alimentares. Objetivo: Avaliar a correlação entre a presença da gordura visceral e subcutânea à resistência insulínica, síndrome metabólica, medidas antropométricas e hábitos alimentares em pacientes portadores DHGNA. Resultados: Sessenta por cento dos pacientes com DHGNA apresentavam Síndrome Plurimetabólica de acordo com os critérios do ATP III. Dentre os critérios mais prevalentes da síndrome metabólica, níveis baixos HDL e circunferência de cintura (CC) aumentada ocorreram em 56%. Ao dividirmos os pacientes em grupos, os critérios se modificaram. Nos pacientes portadores de esteatose simples, o critério mais prevalente foi CC 77%. Já naqueles com ENA o aumento do nível de triglicérides ocorreu em 68% dos pacientes, sendo o de maior prevalência. As correlações entre CT e IMC (p=0,001), CC (p=0,003) e percentual de massa gorda (p=0,031), apresentam significância estatística negativa entre os pacientes com DHGNA. Não houve significância estatística entre CT e HOMA, ingestão total de energia, proteínas, carboidratos e lipídios nestes pacientes mesmo quando foram divididos de acordo com o grau de inflamação, esteatose e ENA. Por outro lado, a CC ao ser correlacionada com IMC (p=0,000), HOMA (p=0,049), ingestão total de energia (p=0,043), lipídios e dos ácidos graxos mono (p=0,020) e poliinsaturados (0,045) apresentaram significância estatística nos pacientes com DHGNA. Quando divididos segundo o grau de esteatose houve correlação positiva entre CC e HOMA (p=0,045) nos pacientes com esteatose simples. Já nos pacientes portadores de ENA houve correlação positiva entre CC e ingestão total de calorias (p=0,031). Houve diferença estatística positiva quanto ao consumo de lipídios totais (p=0,005) entre o grupo de esteatose e ENA, onde os pacientes com ENA, tinham um maior consumo de lipídios. Conclusões: A circunferência de cintura se mostrou melhor parâmetro de diagnóstico complementar ao ser comparado com a tomografia computadorizada em pacientes com DHGNA. Ao associarmos o IMC com a CC conseguimos obter uma avaliação nutricional mais fidedigna dos riscos de doenças decorrentes da síndrome metabólica. O alto consumo de lipídios apresentou correlação positiva com maior grau de inflamação em pacientes com DHGNA. / Introduction: The dramatic increasing of obesity in the world is a predictive factor to increase the prevalence of chronic diseases, as type II diabetes, hypertension and Nonalcoholic fatty liver disease (NAFLD). It is part of large spectrum of liver damage ranging from simple steatosis and cirrhosis. The pathogenesis of NAFLD is multifactorial and some points in the mechanisms and therapeutic still unknown. The insulin resistance is the major risk factors, recognized in the pathophysiology of NAFLD and it is strongly related with life style and diet. Objective: Evaluate the correlation between visceral and subcutaneous fat with insulin resistance, presence of metabolic syndrome, anthropometric measurements and dietary intake in patients with NAFLD. Results: Sixty percent of patients with NAFLD, classified by ATPIII criteria, had the metabolic syndrome. Waist circumference and low HDL -C were the most positive criteria, observed in 56% of total cases. However the criteria modifies when the group were divided. In patients with simple steatosis WC was the most prevalent criteria 77%, where as in NASH patients the high level of TGL 68%, was the most prevalent. Correlations between CT and BMI (p=0,001), WC (p=0,033) and fat mass (p =0,031) had a negative statistic significant correlation in all cases of NAFLD. No significant associations were found between CT (umbilical circumference) and fat mass, WC, HOMA, Intake of calories, carbohydrates, proteins, lipids and fat acids in patients divided in steatosis and NASH patients. The correlation between Waist circumference (WC) with BMI (p=0,000), HOMA (p:0,049), total of energy intake (p=0,043) , monounsaturated (p:0,020) and polyunsaturated (p:0,045) fat acids intake showed a statistic significance in all cases of NAFLD. Significant different correlations were found as the group were divided in steatosis and NASH cases. The values of fat mass correlated with WC was (p: 0,045) in the steatosis group where as in NASH patients the only correlation found was WC and total consumption of daily energy (p=0,031). NASH patients showed a statistic higher intake of lipids (p=0,005), compared with steatosis patients. Conclusions: CT measurement of visceral fat did not contribute to differential diagnosis as much as WC in patients with NAFLD. The use of both measurements BMI and WC showed to be a better predictor of the risks of Metabolic Syndromes. NASH subjects had a higher intake o total fat as well as of lipid fractions.

A expansão rápida da maxila assistida cirurgicamente (ERMAC) é o procedimento de eleição para o tratamento da deficiência transversa de maxila em pacientes esqueleticamente maduros. Controvérsias em relação ao procedimento ainda persistem principalmente relacionadas aos métodos de avaliação, técnica cirúrgica utilizada, morbidade, eficácia clínica e estabilidade de resultados. A utilização da tomografia computadorizada para a avaliação da eficiência da ERMAC é uma opção atual e ainda pouco divulgada. Consequentemente, os parâmetros anatômicos para a utilização deste método ainda não foram totalmente estabelecidos. Os objetivos do presente estudo foram avaliar a confiabilidade da metodologia proposta e as alterações esqueléticas maxilares decorrentes da ERMAC com a utilização do método de avaliação por tomografia computadorizada. No período de junho de 2004 a maio de 2005, 15 pacientes, sendo 10 do sexo feminino, foram submetidos a ERMAC. A técnica cirúrgica utilizada constou de osteotomia maxilar do tipo Le Fort I, sem osteotomia da sutura ptérigo-maxilar, associada a osteotomia sagital mediana do palato. O aparelho expansor utilizado foi do tipo Hyrax. Os pacientes foram submetidos a exames de tomografia computadorizada, em tomógrafos de múltiplos detectores, no pré-operatório e após 6 meses, utilizando-se metodologia idealizada para a avaliação específica deste procedimento cirúrgico. Para a determinação do padrão das alterações transversais e ântero-posteriores, medidas lineares e angulares foram realizadas diretamente na estação de trabalho dos aparelhos de tomografia. Através de imagens obtidas nas aquisições tomográficas axiais e em reconstruções coronais, as regiões anterior, média e posterior da maxila foram avaliadas separadamente. A área de secção transversa da maxila foi também calculada. Após a avaliação dos resultados observou-se que a confiabilidade do método foi estatisticamente comprovada. Um significativo aumento da área de secção transversa da maxila foi observado (p<0.05). Entretanto, o padrão de expansão transversa não se mostrou uniforme. O aumento das dimensões transversas nas regiões anterior e média foi estatisticamente comprovado. Não foi observada expansão transversa significativa na região posterior da maxila. Ao se avaliar a relação entre a abertura do parafuso expansor e a efetiva expansão esquelética da maxila, observou-se que esta foi menor que a abertura do parafuso, em termos absolutos. O aumento transverso relativo à expansão do parafuso foi estatisticamente maior nas regiões anterior e média da maxila do que em sua região posterior. Em conclusão, a avaliação por tomografia computadorizada para a análise das alterações esqueléticas da região maxilar, em pacientes submetidos à ERMAC é metodologia confiável e reprodutível. A expansão transversa da maxila decorrente do procedimento de ERMAC utilizado no presente estudo acarretou uma expansão não uniforme da maxila, com predomínio da expansão transversa nas regiões anterior e média. / Surgically assisted rapid palatal expansion is the procedure of choice for treating transverse maxillary deficiency in mature patients. Some controversies regarding surgically assisted rapid palatal expansion remain, mainly concerning technical aspects such as type and location of osteotomy sites, as well as surgical morbidity, clinical efficiency, and stability. The evaluation of transverse expansion is still a theme of discussion. On conventional anteroposterior radiographs, anatomical structures are superimposed, resulting in a high number of image artifacts, as well as hindering the tracing and evaluation. The use of computed tomography as a method of evaluating the efficiency of this procedure has not been widely reported. Consequently, few landmarks for use in evaluating maxillary expansion have been defined. The goals of the present study were to define parameters to assess skeletal changes after surgically assisted palatal expansion, to evaluate the reliability of the proposed method and to use computed tomography to assess those parameters. From June of 2004 to May of 2005, 15 patients underwent surgically assisted rapid palatal expansion (a modified Le Fort I maxillary osteotomy without pterygomaxillary separation, together with a sagital palatal osteotomy) according to a defined protocol, using a Hyrax appliance. To determine the pattern of transversal and anteroposterior expansion, linear and angular measurements were performed on multislice computed tomography, using computed software directly on the workstation. The anterior, intermediate and posterior portions of the maxilla were evaluated separately, using a specific method, in axial acquisition and coronal reconstructed views. The cross-sectional area of the maxilla was calculated to obtain general information about maxillary expansion. The reliability of the method was statistically confirmed. Significant maxillary overall expansion was observed. However, different patterns of expansion were seen in the three regions analyzed. In the anterior and intermediate portions of the maxilla, the increase in maxillary width was significantly greater than that observed in the posterior portion. The opening of the jackscrew was greater than skeletal expansion. Comparing jackscrew opening and transverse expansion, the same pattern of asymmetric expansion was verified. No change was observed in anteroposterior dimensions. The method of computed tomography evaluation is a useful tool for evaluation of surgically assisted rapid palatal expansion changes. The accurate evaluation of the postoperative changes was heavily dependent upon images acquired through computed tomography. An overall maxillary expansion was confirmed. However, transverse expansion of the maxilla achieved through surgically assisted rapid palatal expansion without pterygoid plate separation was less than uniform.