Reducing the amount of radiation in X-ray computed tomography has been an active area of research in the recent years. The reduction of radiation has the downside of degrading the quality of the CT scans by increasing the ratio of the noise. Therefore, some techniques must be utilized to enhance the quality of images. In this research, we approach the denoising problem using two class of algorithms and we reduce the noise in CT scans that have been acquired with 75% less dose to the patient compared to the normal dose scans. Initially, we implemented wavelet denoising to successfully reduce the noise in low-dose X-ray computed tomography (CT) images. The denoising was improved by finding the optimal threshold value instead of a non-optimal selected value. The mean structural similarity (MSSIM) index was used as the objective function for the optimization. The denoising performance of combinations of wavelet families, wavelet orders, decomposition levels, and thresholding methods were investigated. Results of this study have revealed the best combinations of wavelet orders and decomposition levels for low dose CT denoising. In addition, a new shrinkage function is proposed that provides better denoising results compared to the traditional ones without requiring a selected parameter. Alternatively, convolutional neural networks were employed using different architectures to resolve the same denoising problem. This new approach improved denoising even more in comparison to the wavelet denoising. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2018. / FAU Electronic Theses and Dissertations Collection

The research reported in this PhD thesis provides a novel approach to estimate 3D pitting corrosion kinetics of austenitic stainless steel with exposure to chloride-containing aqueous environments. A quasi-in-situ X-ray computed tomography (X-ray CT) approach was developed, with the aim of providing an experimental methodology to estimate 3D pitting corrosion kinetics under different exposure conditions. The first part summarises a set of preliminary investigations to identify the pitting corrosion behaviour of three austenitic stainless steels (type 303 bar, type 304 plate and type 304L wire) with different inclusion contents. All observed pit densities were related to the inclusion contents, providing confidence in moving to the next stage of the project, for conducting in-situ corrosion studies using X-ray CT. The second section describes the construction of an in-situ electrochemical cell for X-ray CT studies, the aim being to provide an experimental methodology to estimate 3D pitting corrosion kinetics. Pit growth kinetics of individual pits were estimated from segmented 3D X-ray CT data. The evolution of pit current densities, associated pit stability products, and diffusivity parameters over time were obtained. The study also showed that the kinetics of multiple pits could be estimated using this novel approach, based on separating the current response of each pit over time. This was obtained by electrochemical polarisation control and measuring the total current evolution. The third section discusses the effect of plastic strain on 3D pitting corrosion kinetics. Several in-situ X-ray CT experiments were conducted, with a focus on obtaining 3D pit growth, passivation, and re-activation kinetics, to elucidate the effect of applied strain on pit stability and growth. This section explains a possible mechanism for the re-activation of pre-existing corrosion pits, showing that pits grew more rapidly during reactivation than those grown before plastic strain was applied. A marked difference in pit morphology with fractured lacy metal covers was observed with the application of strain. The implications of this observation are discussed in light of stress corrosion crack nucleation mechanisms.

Orientador: Solange Maria de Almeida / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Odontologia de Piracicaba / Made available in DSpace on 2018-09-11T21:16:55Z (GMT). No. of bitstreams: 1 Silva_IsabelaMariadeCarvalhoCrusoe_M.pdf: 2322395 bytes, checksum: 2378f18e1c22e49e20d1b9f0670b3d52 (MD5) Previous issue date: 2011 / Resumo: O objetivo no presente estudo foi comparar os coeficientes das unidades de Hounsfield (HU) em imagens adquiridas por tomografia de Feixe Cônico e tomografia multislice. Para tanto, foram utilizadas imagens de vinte mandíbulas maceradas adquiridas em dois tomógrafos: tomógrafo multislice de 40 canais (Somatom Sensation 40 - Siemens) com protocolo de cortes axiais de 0,7 mm de espessura e intervalo entre os cortes de 0,5 mm; e tomógrafo de feixe cônico i-CAT (Imaging Sciences International), com cortes axiais de 0,2 mm de espessura, tempo de aquisição de 40 segundos e Field of View (FOV) de 8 cm. As análises das imagens foram feitas pelos softwares Syngo CT (tomógrafo multislice). Os valores obtidos por este último foram considerados como Padrão Ouro. Para as mensurações foram utilizadas as coordenadas X e Y, bem como a ferramenta de HU de ambos os softwares. Ficando assim, viável a comparação dos resultados após as Análises Estatísticas Descritivas e do Teste t pareado. Os dados obtidos indicaram um valor médio das regiões de interesse de 313,13 HU para a tomografia multislice e de 418.06 HU para a tomografia de feixe cônico, com valor de P < 0,001. Portanto, os valores de HU, obtidos pelo software da tomografia de feixe cônico, apresentaram-se superestimados em relação aos encontrados no Tomógrafo multislice. Na ausência de correspondência entre os dados amostrados, a tomografia de feixe cônico não oferece segurança e credibilidade ao cirurgião-dentista na avaliação da densidade óssea no planejamento para implantes e em cirurgias do complexo maxilofacial / Abstract: The aim of this study was to compare the attenuation coefficients (Hounsfield Unit) in both cone-beam computed tomography (CT) and multislice CT images. The 40-channel CT scanner (SOMATOM Sensation 40 - Siemens) was used to obtain images (n=20) of macerated mandibles considering the following protocol: axial slices of 0.7 mm in thickness and an interval of 0.5 mm between cuts. This same sample was submitted to i-CAT cone-beam CT scanner (Imaging Sciences International): axial slices of 0.2 mm in thickness and a field of view of 8 cm. Images were analyzed by means of computer software - XoranCat (cone-beam CT scan) and the Syngo CT (multislice CT scan) - the latter of which was considered Gold Standard. Coordinates X and Y and the HU tool were used for the measurements. Data were submitted to the descriptive statistical analysis and the paired sample t-test. A mean value of 313.13 HU was obtained for Multislice CT and 418.06 HU for the cone-beam CT (p<0.001). The attenuation coefficient values obtained for the cone-beam CT were overestimated when compared to those for the multislice CT. Since no correspondence was found among the data sampled, cone-beam CT offers no credibility for the dentist to evaluate bone during planning of implant and/or maxillofacial complex surgery / Mestrado / Radiologia Odontologica / Mestre em Radiologia Odontológica

As tomografias computadorizadas de feixe cônico (TCFC) vêm ganhando espaço no cenário odontológico devido ao detalhamento das imagens, sem sobreposição de estruturas anatômicas. O objetivo do presente estudo foi comparar a acurácia e a precisão da tomografia computadorizada de feixe cônico e de radiografias periapicais na detecção de defeitos ósseos interproximais artificiais de diferentes tamanhos. Após cálculo amostral, foram adquiridas 20 mandíbulas suínas, nas quais foi empregada cera para simulação de tecido mole e proteção das faces interproximais dos dentes. Das 80 áreas experimentais (entre 1º e 2º pré-molares e entre 2º pré-molar e 1º molar), após aleatorização, foram criadas 60 lesões (20 com exposição ao ácido por 2 horas, 20 com exposição ao ácido por 4 horas e 20 com exposição ao ácido por 6 horas). Em 20 áreas não foram produzidas lesões (controles). As lesões foram criadas com ácido perclórico 70-72%, aplicado com bolinha de algodão. TCFC e radiografias periapicais foram realizadas e depois analisadas por dois radiologistas treinados. A presença de lesões na mandíbula seca foi considerada o padrão-ouro. Foi calculada a sensibilidade, a especificidade e a acurácia da tomografia e da radiografia periapical na detecção das lesões de diferentes tamanhos. A acurácia da TCFC variou de 0,688 a 0,775 e a da radiografia variou de 0,700 a 0,763. Além disso, o tamanho da lesão influenciou no resultado, sendo que lesões de 6h geraram menos resultados falso-negativos do que as lesões de 2h, em ambos os exames. A reprodutibilidade foi aferida pelo coeficiente kappa. A concordância interexaminador variou de ausente a razoável, enquanto a concordância intraexaminador variou de boa a muito boa. Concluímos que não houve diferença com relação à acurácia da TCFC e da radiografia periapical na detecção de defeitos ósseos interproximais artificiais em mandíbulas suínas. / Cone beam computed tomography (CBCT) has been considered an advance in dentistry imaging due to its high quality tridimensional images. The aim of this study was to evaluate accuracy and precision of CBCT and periapical radiographs in detecting artificial interproximal alveolar bone lesions of different sizes. After sample size calculation, 20 swine mandibles were acquired and had all soft tissue removed. Red wax was used for soft tissue simulation and to protect interproximal aspects of teeth. After randomization, sixty lesions were created (20 with 2 hour acid exposure, 20 with 4 hour acid exposure and 20 with 6 hour acid exposure) and in 20 areas (controls) no lesions were created, totalizing 80 experimental sites. Bone lesions were produced in experimental areas (between 1st and 2nd premolars and between 2nd premolar and 1st molar) with the use of a cotton pellet soaked in perchloric acid 70-72%. CBCT and periapical radiographs were taken and then analyzed by two trained radiologists. The presence of lesions in the dry mandible was considered the gold standard. Sensitivity, specificity and accuracy in detecting different-sized bone lesions were calculated for CBCT and periapical radiography. Accuracy of CBCT ranged from 0,688 a 0,775 and accuracy of periapical radiography ranged from 0,700 a 0,763. The size of lesion influenced results, since 6h-lesions presented less false-negative results than 2h-lesions, in both exams. Reproducibility was measured by kappa coefficient. Interexaminer concordance varied from none to fair, whereas intraexaminer concordance varied from moderate to substantial. Therefore, we concluded that there was no difference between CBCT and periapical radiography accuracy as regards to detection of artificial interproximal bone lesions in swine mandibles.

The compressive strength of unidirectional (UD) carbon fibre reinforced plastics (CFRPs) is often only 60-70% of their tensile strength owing to premature failure associated with kink-band formation. The sudden and complex nature of kink-band formation has been hindering the progress in experimental studies on the evolution of damage in compressive failure. A better understanding of the damage mechanisms associated with kink-band formation can help to design more reliable composite structures. Therefore, the principal aim of this project is to identify, in three dimensions (3D), the key damage mechanisms underlying the initiation and propagation of kink bands in UD carbon fibre/epoxy composite. A new manufacturing method is developed to fabricate high-quality UD T700/epoxy cylindrical rods for axial compression tests and high-resolution imaging of kink bands by post mortem and in situ X-ray computed tomography (CT). The morphology of kink bands is visualised in 3D by segmenting fibre breaks at kink-band boundaries and representative longitudinal splits. The geometrical parameters of each fully developed kink band are consistent through the specimen. Radiographs obtained from ultra-fast synchrotron imaging show that a kink band initiates and propagates across the specimen in less than 1.2 ms. A scenario of kink-band failure is proposed: fibre buckling and longitudinal splitting occur prior to fibre breakage, which forms kink-band boundaries and eventually the morphology of multiple kink bands develops suddenly. 3D tomographs of the fast and unstable kink-band formation could not be captured in the axial compression experiments. Therefore, a testing method of loading notched UD carbon fibre (T800, T700 and T300)/epoxy beams using a four-point bending (FPB) fixture is developed to enable monitoring of more stable initiation and propagation of kink bands by in situ X-ray CT. Kink-band formation is significantly slowed in the FPB tests. Fibre micro-buckling accompanied by splitting, could initiate the formation of kink bands. In the T700/epoxy system, the early initiation stage of fibre micro-buckling without fracture is captured, and the critical radius of curvature of unbroken fibres prior to fracture is ～130micro metre. Unloading causes significant recovery of fibre curvature (radius of curvature ～280 micro metre) and a reduction of 10-20º in fibre rotation angle within the kink band. The results show that in situ 3D characterisation of kink bands is essential as fibre buckling is a 3D phenomenon, resulting in development of both in-plane and out-of-plane kink bands. Understanding of kink-band formation in 3D will help to establish strategies to improve the compressive strength of CFRP composites by depressing kink-band formation; in this respect lateral constraint conferred by strong interfaces is a key aspect.

Selective electron beam melting (SEBM) is a promising powder bed Additive Manufacturing technique for near-net-shape manufacture of high-value titanium components. An extensive research program has been carried out to characterise in 3D the size, volume fraction, and spatial distribution of the pores in model samples, using X-ray computed tomography (XCT), and correlate them to the SEBM process variables. The average volume fraction of the pores (97.5 %) where fatigue cracks would initiate based on the relative stress intensity factor of all the pores. In contrast, crack growth was found to be insensitive to porosity, which was attributed to the much higher stress concentration generated by the crack in comparison to the pores. Some crack diversion was associated with the local microstructure, with prior β grain boundaries often coincident with crack diversion.

Carbonate rocks are of global importance as they contain about 50% of the world’s remaining hydrocarbon reserves and are also a major host to the world’s groundwater resources. Therefore, understanding and modelling the fluid flow processes in carbonates are of great importance. A critical problem is that, unlike homogenous media (such as sandstones), carbonates often show features, including porosity, that span across a wide spatial range, from sub-micron porosity to fractures of meters length-scale. In this study X-ray computed micro-tomography (μCT) has been utilised as a tool to monitor two phase (oil-brine) flow in porous carbonate (dolomite) plugs at ambient temperature and pressures smaller than 690 kPa. A simple, low-cost and highly X-ray transparent core-holder was utilised for which the design is introduced. Capillary end effects were recognised and avoided in data analysis. Displacement processes that occur in the dolomite under water-wet, oil-wet, and partially mixed-wet states were investigated. The experiments consisted of a series of drainage and imbibition processes occurring under capillary and viscous dominated flow regimes. Pore-scale mechanisms of piston-like displacement and snap-off (or at least clear results of them), that were previously observed in sandstones and 2D micro-models, were observed in the dolomite under study. In addition, a new pore-scale mechanism was identified which occurred at high capillary numbers, referred to as droplet-fragmentation. This new pore-scale mechanism may provide an explanation to the capillary-desaturation process for heterogeneous media. In the experiments performed on the oil-wet plug formation of a stable water in oil emulsion was observed which appears to be the first 3D observation of in situ emulsion formation made using μCT. Direct visualisation of the oil-brine-rock configurations and measurement of the contact angles are presented. A comparison was made for the contact angle distributions measured for the water-wet and oil-wet conditions. Observation of fluid displacement processes as well as oil-brine-rock contact angle distributions demonstrate that pore-scale imaging provides a promising tool for wettability characterisation on both pore and core scales. Such detailed wettability data can also be used in pore-scale flow models. For the dolomite under study multiple-scale pore network models were constructed by integrating single-scale networks extracted from μCT images acquired at different length-scales. Mercury injection capillary pressure laboratory measurements were used to evaluate the capillary pressure (vs. saturation) curves calculated using single, two-scale, and three-scale network models of this dolomite. The integrated networks displayed an improved match to the laboratory measurements in comparison with the single-scale network model. The three-scale network provided the closest simulated curve, this result confirms that a more representative model displays closer properties. While simulated capillary pressure curves are close (converging) for the integrated networks the calculated relative permeability curves show variability for different multiple-scale networks. The present work demonstrates that the pore-scale fluid displacement processes occurring in heterogeneous porous media are more complex than those occurring in homogeneous media. In addition, successful fluid flow simulations require construction of multiple-scale models as well as consideration of the pore-scale processes (such as droplet-fragmentation) that are specific to such complex pore systems.

Submitted by Fabíola Silva (fabiola.silva@famerp.br) on 2016-09-14T18:04:46Z No. of bitstreams: 1 samiraelhassan_dissert.pdf: 845797 bytes, checksum: 9cdbef0eb8a8206334b32172283744d7 (MD5) / Made available in DSpace on 2016-09-14T18:04:46Z (GMT). No. of bitstreams: 1 samiraelhassan_dissert.pdf: 845797 bytes, checksum: 9cdbef0eb8a8206334b32172283744d7 (MD5) Previous issue date: 2014-09-23 / Introduction: Acute appendicitis is the process of the inflamation of the appendix and it is the most frequent cause of acute abdomen. About 50% of patients with acute appendicitis show classic clinical findings. The others have atypical manisfestations which make diagnosis more difficult, such as in pregnant women, women of childbearing age, and patients younger than ten and more than fifty years of age. At the time of surgery, approximately 35% of the cases are in the advanced phase with perforation and local abscesses. Methods of diagnosis such as ultrasonography and computed tomography can help in the diagnosis of acute appendicitis minimizing surgical delay and reducing appendix perforation and unnecesarry appendectomies. Patients with typical signs and symptoms of acute appendicitis should be assessed and undergo appendectomy. Those with atypical presentation should have image exams. First, they should have an ultrasonography. If the exam doesn't present clearly or if it isn't conclusive, computed tomography should be performed. Objetive: Determine sensitivity and specificity of ultrasonography and computed tomography of patients suspected of having acute appendicitis. Verify a positive diagnosis of acute appendicitis by computed tomography when ultrasonography results are negative in patients suspected of acute appendicitis. Casuistic and method: Prospectively, we analyzed 60 patients, from January of 2006 to May of 2007, between 2 and 90 years old, of both sexes, from the Surgery Department of the Hospital de Base de São Jose do Rio Preto who have been sent to the Radiology Department (Ultrasonography and Tomography Unit) of the above mentioned hospital. The ultrasonography exams were done with a graded compression technique. The computed tomography exams were realized with colonic contrast administered rectally. The conventional axial images of 5 mm of thickness were taken from the pelvic region. Afterwards, iodine contrast was given intravenously and tomographic sections were taken by the helical technique with 5mm of thickness in the pelvic region. After this, other sections of 10mm of thickness were taken of the entire abdomen. Results: Of 60 patients that had ultrasonography, 40 (66.67%) presented positive exams for acute appendicitis. The ultrasonography sensitivity for acute appendicitis was 100%, while the specificity was 83.33%. Of 27 patients that underwent computed tomography, 19 (70.37%) presented negative exams for acute appendicitis. The sensitivity of computed tomography to acute appendicitis was 100%, and the specificity was 33.33%. Conclusion: The diagnosis of acute appendicitis by imaging methods helps to reduce the frequency of unnecessary appendicetomies, frequent complications because of delayed diagnosis, the costs of exams, and long hospital stays. / Introdução: A apendicite aguda é o processo inflamatório do apêndice cecal e a causa mais frequente de abdome agudo. Cerca de 50% dos pacientes com apendicite aguda apresentam quadro clínico clássico. Os demais apresentam manifestações atípicas, o que dificulta o diagnóstico, principalmente gestantes, mulheres em idade reprodutiva, pacientes com menos de 10 anos e com mais de 50 anos de idade. Em aproximadamente 35% dos casos, a apendicite já está em fase adiantada, com perfuração e abscesso local, no momento da cirurgia. Métodos de diagnóstico, ultrassonografia e tomografia computadorizada, podem auxiliar no diagnóstico da apendicite aguda, minimizando o atraso na cirurgia, com subsequente redução do risco de perfuração do apêndice cecal e de apendicectomias negativas. Pacientes com sinais e sintomas típicos de apendicite aguda devem ser prontamente avaliados e conduzidos à apendicectomia. Aqueles, com apresentação ou achados atípicos, devem realizar exames de imagem. Objetivo: Determinar em pacientes com suspeita de apendicite aguda a relação dos resultados do US e TC com os sinais e sintomas clínicos, a sensibilidade e a especificidade da ultrassonografia e da tomografia computadorizada e a positividade da tomografia computadorizada, quando o ultrassom for negativo. Casuística e Método: Foram analisados, prospectivamente, 60 indivíduos no período de janeiro de 2006 a maio de 2007, com idade entre 2 a 90 anos, de ambos os gêneros, procedentes do Departamento de Cirurgia do Hospital de Base de São José do Rio Preto-SP e encaminhados para o setor de ultrassonografia e de tomografia computadorizada do Departamento de Radiologia, no referido hospital. Os exames de ultrassom foram realizados com a técnica de compressão gradual. Os exames de tomografia computadorizada foram realizados com contraste colônico via retal. Foram realizadas imagens axiais convencionais de 5 mm de espessura na região pélvica. Posteriormente, foi administrado contraste iodado endovenoso e foram realizados cortes tomográficos pela técnica helicoidal com 5 mm de espessura na região pélvica. Em seguida, foram realizados cortes tardios de 10 mm de espessura em todo o abdome. Resultados: Dos 60 pacientes que realizaram US, 40 (66,67%) apresentaram exames positivos para apendicite aguda. A sensibilidade do US, para apendicite aguda, foi de 100%, a especificidade de 83,33%. Dos 27 pacientes submetidos à TC, 19 (70,37%) apresentaram exames negativos para apendicite aguda. A sensibilidade da TC, para apendicite aguda foi, de 100%, a especificidade de 33,33%. Conclusão: O diagnóstico da apendicite aguda, por métodos de imagem, contribui para a redução na frequência de apendicectomias negativas, de complicações decorrentes do atraso do seu diagnóstico, dos custos com exames e das internações prolongadas.

Ma, Ka Lim. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references (leaves [110]-117). / Abstracts in English and Chinese. / Chapter 1 --- Radon Transform and Medical Tomography --- p.1 / Chapter 1.1 --- Computed Tomography --- p.2 / Chapter 1.2 --- Emission Computed Tomography --- p.4 / Chapter 1.2.1 --- SPECT --- p.5 / Chapter 1.2.2 --- PET --- p.6 / Chapter 1.3 --- Radon Transform --- p.8 / Chapter 1.3.1 --- Properties of Radon Transform --- p.10 / Chapter 1.3.2 --- Fourier Slice Theorem --- p.11 / Chapter 1.4 --- Research Objective --- p.12 / Chapter 2 --- Popular Tomographic Reconstruction Algorithms --- p.14 / Chapter 2.1 --- Analytic Method --- p.15 / Chapter 2.1.1 --- Direct Fourier Method (DFM) --- p.15 / Chapter 2.1.2 --- Backprojection (BP) --- p.17 / Chapter 2.1.3 --- Backprojection Filtering (BPF) --- p.19 / Chapter 2.1.4 --- Filtered Backprojection (FBP) --- p.21 / Chapter 2.2 --- Iterative Method --- p.23 / Chapter 2.2.1 --- Maximum Likelihood - Expectation Maximization (ML-EM) --- p.25 / Chapter 2.2.2 --- Ordered Subsets Expectation Maximization (OSEM) --- p.27 / Chapter 3 --- Consistent Reconstruction --- p.30 / Chapter 3.1 --- Directional Filter Bank (DFB) --- p.30 / Chapter 3.1.1 --- Interpolation in horizontal function space --- p.32 / Chapter 3.1.2 --- Directional Multiresolution Analysis --- p.33 / Chapter 3.1.3 --- Iterated Filter Bank Equivalence --- p.36 / Chapter 3.1.4 --- Vertical Directional Function Space --- p.38 / Chapter 3.1.5 --- Summary --- p.40 / Chapter 3.2 --- Reconstruction Scheme --- p.42 / Chapter 3.2.1 --- Choices for basis function 6m --- p.43 / Chapter 3.2.2 --- Choices for coordinate mapping function wm --- p.46 / Chapter 3.2.3 --- Summary --- p.49 / Chapter 3.3 --- Experiment --- p.49 / Chapter 3.3.1 --- Experiment for consistent reconstruction with different choices --- p.50 / Chapter 3.3.2 --- Experiment for comparison with different reconstruction methods --- p.54 / Chapter 3.4 --- Conclusion --- p.56 / Chapter 4 --- Tomographic Denoising --- p.57 / Chapter 4.1 --- SURE-LET and PURE-LET denoising --- p.59 / Chapter 4.1.1 --- SURE-LET --- p.60 / Chapter 4.1.2 --- PURE-LET --- p.62 / Chapter 4.2 --- Experiment --- p.64 / Chapter 4.2.1 --- Experiment on SURE-LET Denoising --- p.65 / Chapter 4.2.2 --- Experiment on PURE-LET Denoising --- p.69 / Chapter 4.2.3 --- Conclusion --- p.76 / Chapter 5 --- Sinogram Retrieval --- p.77 / Chapter 5.1 --- Sinogram Retrieval Method --- p.78 / Chapter 5.1.1 --- MATLAB Radon Function --- p.79 / Chapter 5.1.2 --- Subordinate Gradient (SG) Algorithm --- p.81 / Chapter 5.1.3 --- Orthonormal Subordinate Gradient (OSG) Algorithm --- p.81 / Chapter 5.2 --- Experiment --- p.84 / Chapter 5.2.1 --- Limitation of Sinogram Retrieval --- p.84 / Chapter 5.2.2 --- Comparison of Sinogram Retrieval Algorithms --- p.86 / Chapter 5.2.3 --- Embedded in Tomographic Reconstruction --- p.88 / Chapter 5.2.4 --- Embedded in Tomographic Denoising --- p.90 / Chapter 5.3 --- Conclusion --- p.96 / Chapter 6 --- Conclusion --- p.97 / Chapter 6.1 --- Summary --- p.97 / Chapter 6.1.1 --- Tomographic Reconstruction --- p.97 / Chapter 6.1.2 --- Tomographic Denoising --- p.98 / Chapter 6.1.3 --- Sinogram Retrieval --- p.98 / Chapter 6.2 --- Future Research --- p.99 / Chapter 6.2.1 --- Tomographic Reconstruction --- p.99 / Chapter 6.2.2 --- Tomographic Denoising --- p.99 / Chapter 6.2.3 --- Sinogram Retrieval --- p.99 / Chapter A --- Examples of Radon Transform --- p.100 / Chapter B --- Experimental Phantom Image --- p.104 / Chapter C --- Results of sinogram retrieval experiments --- p.107 / Bibliography --- p.110

As tomografias computadorizadas de feixe cônico (TCFC) vêm ganhando espaço no cenário odontológico devido ao detalhamento das imagens, sem sobreposição de estruturas anatômicas. O objetivo do presente estudo foi comparar a acurácia e a precisão da tomografia computadorizada de feixe cônico e de radiografias periapicais na detecção de defeitos ósseos interproximais artificiais de diferentes tamanhos. Após cálculo amostral, foram adquiridas 20 mandíbulas suínas, nas quais foi empregada cera para simulação de tecido mole e proteção das faces interproximais dos dentes. Das 80 áreas experimentais (entre 1º e 2º pré-molares e entre 2º pré-molar e 1º molar), após aleatorização, foram criadas 60 lesões (20 com exposição ao ácido por 2 horas, 20 com exposição ao ácido por 4 horas e 20 com exposição ao ácido por 6 horas). Em 20 áreas não foram produzidas lesões (controles). As lesões foram criadas com ácido perclórico 70-72%, aplicado com bolinha de algodão. TCFC e radiografias periapicais foram realizadas e depois analisadas por dois radiologistas treinados. A presença de lesões na mandíbula seca foi considerada o padrão-ouro. Foi calculada a sensibilidade, a especificidade e a acurácia da tomografia e da radiografia periapical na detecção das lesões de diferentes tamanhos. A acurácia da TCFC variou de 0,688 a 0,775 e a da radiografia variou de 0,700 a 0,763. Além disso, o tamanho da lesão influenciou no resultado, sendo que lesões de 6h geraram menos resultados falso-negativos do que as lesões de 2h, em ambos os exames. A reprodutibilidade foi aferida pelo coeficiente kappa. A concordância interexaminador variou de ausente a razoável, enquanto a concordância intraexaminador variou de boa a muito boa. Concluímos que não houve diferença com relação à acurácia da TCFC e da radiografia periapical na detecção de defeitos ósseos interproximais artificiais em mandíbulas suínas. / Cone beam computed tomography (CBCT) has been considered an advance in dentistry imaging due to its high quality tridimensional images. The aim of this study was to evaluate accuracy and precision of CBCT and periapical radiographs in detecting artificial interproximal alveolar bone lesions of different sizes. After sample size calculation, 20 swine mandibles were acquired and had all soft tissue removed. Red wax was used for soft tissue simulation and to protect interproximal aspects of teeth. After randomization, sixty lesions were created (20 with 2 hour acid exposure, 20 with 4 hour acid exposure and 20 with 6 hour acid exposure) and in 20 areas (controls) no lesions were created, totalizing 80 experimental sites. Bone lesions were produced in experimental areas (between 1st and 2nd premolars and between 2nd premolar and 1st molar) with the use of a cotton pellet soaked in perchloric acid 70-72%. CBCT and periapical radiographs were taken and then analyzed by two trained radiologists. The presence of lesions in the dry mandible was considered the gold standard. Sensitivity, specificity and accuracy in detecting different-sized bone lesions were calculated for CBCT and periapical radiography. Accuracy of CBCT ranged from 0,688 a 0,775 and accuracy of periapical radiography ranged from 0,700 a 0,763. The size of lesion influenced results, since 6h-lesions presented less false-negative results than 2h-lesions, in both exams. Reproducibility was measured by kappa coefficient. Interexaminer concordance varied from none to fair, whereas intraexaminer concordance varied from moderate to substantial. Therefore, we concluded that there was no difference between CBCT and periapical radiography accuracy as regards to detection of artificial interproximal bone lesions in swine mandibles.