O objetivo deste trabalho foi avaliar a influência das correções de atenuação e espalhamento na reconstrução quantitativa em SPECT. O estudo foi baseado em diversas simulações de Monte Carlo, com ênfase especial no modelo torso-cardíaco matemático (MCAT). Para a reconstrução, foi utilizado o algoritmo iterativo ML-EM com projetor-retroprojetor modificado pelo mapa de atenuação. Para avaliar a correção de espalhamento, foram simulados os espectros energéticos, com múltiplas ordens de espalhamento Compton. O método da dupla janela de energia (Jaszczak) foi aplicado, devido a sua simplicidade, e as imagens corrigidas foram comparadas com as de fótons primários. Foram analisadas as escolhas das janelas do fotopico e espalhamento, além da dependência do fator de espalhamento k com a distribuição de atividades do objeto. Duas abordagens foram adotadas para a obtenção dos mapas de atenuação: a estimativa do mapa uniforme diretamente dos dados de emissão, sem o uso de imagens de transmissão; e o borramento de mapas não-uniformes, reconstruídos a partir das projeções por transmissão. A estimativa do mapa de atenuação diretamente dos sinogramas de emissão baseou-se nas condições de consistência da transformada de Radon atenuada. Neste caso, foram estudados os efeitos de diferentes contagens e vários coeficientes de atenuação iniciais sobre as imagens corrigidas. Os mapas de atenuação não-uniformes foram borrados com um \"kernei\" gaussiano, aplicados nas correções e os efeitos na quantificação foram analisados. Os espectros energéticos emitidos pelo modelo MCAT mostraram que os fótons espalhados não poderiam ser excluídos a contento, mesmo que fossem utilizadas janelas de aquisição estreitas sobre o fotopico. Em relação a correção de Jaszczak, verificou-se que a escolha das janelas de fotopico e espalhamento é crucial e confirmou-se que o valor de k é altamente dependente do objeto examinado. Dada uma estimativa inicial do mapa de atenuação, o uso das condições de consistência para estimar o mapa de atenuação uniforme, consistente com os dados de emissão do modelo MCAT simulado, resultou sempre em uma mesma forma, para quaisquer valores iniciais do conjunto de parâmetros. Apesar do erro diminuir com o aumento da contagem, o melhor coeficiente de atenuação não pôde ser obtido, mesmo em altas contagens. Isto se deve a presença dos fótons espalhados, que alteraram a solução das condições de consistência, reduzindo as dimensões do mapa. Os resultados indicaram que a correção de espalhamento é o fator mais importante na reconstrução quantitativa em SPECT. Com referência aos efeitos quantitativos da correção de atenuação, não foram observadas diferenças significativas com a utilização dos mapas borrados, enquanto que a correção com mapas uniformes mostrou-se menos eficaz. / The goal of this work is to evaluate the influence of scatter and attenuation correction methods in quantitative SPECT reconstruction. The study was based on several Monte Carlo simulations, with special emphasis on the mathematical cardiac-torso phantom (MCAT). Iterative ML-EM reconstruction with modified projector-backprojector was used. To evaluate the scatter correction, energy spectra were simulated for SPECT imaging including multiple order Compton scattered photons. The dual energy window method proposed by Jaszczak was applied and scatter corrected images were compared with primary photons images. The choice of the scattering and photopeak windows and the dependence of the scatter factor k with the activity distribution were also analysed. Two approaches were adopted for obtaining the maps for attenuation correction: the estimation of the attenuation maps directly from the emission data, without transmission imaging, and the blurring of non-uniform attenuation maps, reconstructed from transmission data. The estimation of attenuation maps directly from the emission sinograms was based on the consistency conditions of attenuated Radon transform. In this case, the effects of different counting rates and various initial attenuation coefficients on the corrected images were studied. The non-uniform attenuation maps were blurred with a gaussian kernel with different variances, applied in further corrections and their effects on quantitation were examined. Analysis of energy spectra emitted from the MCAT phantom showed that scattered photons cannot be totally excluded, even when narrow acquisition windows were used. As far as the Jaszczak correction is concerned, results showed that the choice of photopeak and secondary windows is crucial and that the value of k is highly dependent on the imaged object. Given an initial estimation of the attenuation map with a constant coefficient, the use of consistency conditions to estimate the uniform map, consistent with the emission data of simulated MCAT phantom, resulted in the same shape for any set of initial parameters. In spite of the fact that the error falls with increasing counting rate, higher counts are not able to determine the best attenuation coefficient. This is due to scattered photons, which alter the solution of consistency conditions, reducing the size of estimated maps. Results indicated that the scatter correction is the most important factor inquantitative SPECT reconstruction. Furthermore, no significant differences were observed in the quantitation, when using the blurred non- uniform attenuation maps in attenuation correction, while corrections with uniform maps proved to be less efficient

O diagnóstico precoce de focos de infecção dentários é de fundamental importância para prevenir a ocorrência de maiores injúrias locais ou sistêmicas. Dentre os diversos métodos utilizados para complementar os achados radiológicos das alterações dentoalveolares surge uma alternativa: a cintilografia tomográfica (SPECT/CT), que permite a fusão de achados morfológicos com alterações metabólicas. Com o objetivo de estabelecer o diagnóstico precoce e acurado de processos infecciosos dentários, foram estudadas 320 áreas dentárias em mandíbula e maxila em (10 pacientes de ambos os sexos selecionados por meio de exames clínicos e radiológicos convencionais, seguidos de cintilografia tomográfica com e sem aparato blindador de raios gama. Os exames cintilográficos foram realizados no Serviço de Medicina Nuclear do Hospital Israelita Albert Einstein (HIAE). Para isso, foi administrado para cada paciente o radiofármaco tecnécio 99- metilenodifosfonato (99mTc-MDP) via endovenosa com a dose de 37mBq/3Kg de peso corporal do paciente. Após o período de acúmulo de três horas, foi realizado o protocolo de aquisição de imagens. Todas as imagens foram analisadas por um médico nuclear e um endodontista, com experiência em cintilografia tomográfica. O resultado obtido por meio do exame radiográfico intrabucal pela técnica periapical digital mostraram 6 imagens positivas, em um total de 1,87% da amostra; exame do mapeamento cintilográfico dos ossos da face com a utilização do blindador de raios gâma revelou 9 imagens positivas, correspondendo a 2,81% do total de áreas estudadas, havendo diferença estatisticamente significante ao nível de 95% pelo teste qui-quadrado. Pode-se concluir que o SPECT/CT permitiu identificar as alterações periapicais em maior número quando comparadas ao exame radiográfico periapical e ao mapeamento cintilográfico dos ossos da face com a utilização do blindador de raios gama; o exame de SPCET/CT além de mostrar imagens mais detalhadas, permitiu também localizar com exatidão as áreas alteradas. / The early diagnosis of cases with dental infection is very important to prevent the occurrence of major local or systemic injuries. With many methods used to complement the radiological findings of the bone alterations there\'s the tomographic scintigraphy witch allows the fusion of morphological and metabolic findings. With the objective of the establishment of early diagnosis and accurate dental infectious processes, it was studied 320 dental areas in maxilla and mandible (10 patients) selected randomly, through conventional radiological exams, followed by tomographic scintigraphy with and without intra-oral apparatus. The scintilographic exams were done at the Nuclear Medicine Service of Hospital Israelita Albert Einstein. For that, methylenediphosphonate-technetium-99m (99mTc-MDP) was dispensed intravenous. After the period of accumulation of 3 hours, the image acquisition protocol was taken. This protocol includes images from the top of the head to the neck. After the image analyzes, statistics was done. The intrabucal radiograph exam by the digital periapical technique showed 6 positive images, in a total of 1.87% of the total sample, Intra-oral apparatus showed 9 positive images, in a total os 2,81% of the sample and SPECT/CT exam revealed 15 positive images, corresponding to 4.28% of the total studied areas, showing statistical significance by the level of 95% of qui-square. We could conclude that SPECT/CT allowed identifying the endodontic infections in a larger number when compared with the radiograph exams; and the SPECT/CT exam showed to be of great interest by allowing the union of the diagnosis precocity with the image detail, presenting exact localization of inflammatory/infectious alterations due to the presence of the CT.

The Thesis explores additional applications of LAP's Aquarius external laser alignment verification Phantom by examining geometric accuracy of magnetic resonance images commonly used for planning intracranial stereotactic radiation surgery (ICSRS) cases. The scans were performed with MRI protocols used for ICSRS, and head and neck diagnosis, and their images fused to computerized tomographic (CT) images. The geometric distortions (GDs) were measured against the CT in all axial, sagittal, and coronal directions at different levels. Using the Aquarius Phantom, one is able to detect GD in ICSRS planning MRI acquisitions, and align the external LAP patient alignment lasers, by following the LAP QA protocol. GDs up to about 2 mm are observed at the distal regions of the longitudinal axis in the SRS treatment planning MR images. Based on the results, one may recommend the use of the Aquarius Phantom to determine if margins should be included for SRS treatment planning. / by Daniel Vergara. / Thesis (M.S.)--Florida Atlantic University, 2012. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2012. Mode of access: World Wide Web.

Nesta tese é apresentado um novo método de reconstrução de imagens, por tomografia de transmissão, de projeções sujeitas a ruído na contagem de fótons. O método de reconstrução selecionado utiliza a técnica POCS (Projections Onto Convex Sets). A estimação das projeções originais a partir das observações ruidosas se dá por meio de quatro métodos: a) estimação utilizando o critério MAP (Maximum a Posteriori); b) filtragem nos coeficientes wavelets das projeções ruidosas; c) aplicação do filtro de Wiener pontual e d) aplicação do filtro de Goodman-Belsher. É apresentado o resultado da reconstrução após a estimação das projeções, mostrando o ISNR (Improvement Signal-to-Noise Ratio) entre as imagens reconstruídas, a partir das projeções ruidosas, com a técnica POCS, estimando as projeções e sem a realização da estimação. Foram utilizados, para reconstrução tomográfica, projeções de corpos de prova obtidos por meio de simulação e também projeções obtidas experimentalmente no minitomógrafo do CNPDIA - EMBRAPA. O uso de estimação sobre as projeções ruidosas mostrou-se eficaz para melhorar a relação sinal-ruído na imagem final, pois esse pré-processamento faz com que os conjuntos impostos pelas projeções sejam mais restritivos. Deve-se observar que a melhoria das imagens obtidas com o uso de filtragem das projeções é obtida com uma relação custo-benefício bastante baixa, pois a maior parte do custo computacional está na fase de reconstrução das imagens. / In this thesis is pesented a new method for image reconstruction, by transmission tomography, for projections under noise in the counting of photons. The selected method of reconstruction uses the POCS (Projections Onto Convex Sets) technique. The estimation of the original projections from the noisy projections observed is performed through four methods: a) estimation using the MAP (Maximum a Posteriori) criteria; b) through of filtering of the wavelets coefficients of the noisy projections; c) using the pointwise Wiener filter and d) using the Goodman-Belsher filter. We present the result of reconstruction after projection estimation, showing the ISNR (Improvement Signal-to-Noise Ratio) between the reconstructed images on noisy projections, using POCS technique after the estimated projections and without this estimation. We use, for tomographic reconstruction, test body projections obtained through simulation and also projections obtained experimentally in the minitomograph scanner of CNPDIA-EMBRAPA. The use of estimation on noisy projections demonstrated to be efficient in improving the signalnoise ratio in the final image, since this pre-processing makes the sets that projections more restrictive. We should observe that the use of projection filtering is obtained with a cost-benefit ratio rather low, since the largest part of the computational effort is in the image reconstruction phase.

Introdução:embora seja mundialmente conhecida a correlação entre os escores tomográficos de avaliação isquêmica cerebral com achados e desfechos clínicos em pacientes com acidente vascular cerebral (AVC) isquêmico, são limitadas as evidencias em pacientes do subtipo cardioembólico. Objetivo: avaliar e correlacionar o perfil e desfechos clínicos de pacientes com AVC isquêmico do subtipo cardioembólico com os achados tomográficos de isquemia, segundo escores tomográficos. Métodos:estudo retrospectivo de um grupo de pacientes com AVC do tipo cardioembólico segundo a classificação TOAST, selecionados através de uma amostra de conveniência dos pacientes que foram atendidos em um centro de referência de emergências cerebrovasculares (março de 2014 a março de 2015). Os exames tomográficos destes pacientes foram avaliados por dois observadores (um radiologista com 10 anos e outro com 2 anos de experiência em exames tomográficos) treinados na avaliação de escores tomográficos relacionados a alterações isquêmicas encefálicas e cegados para os dados clínicos e laboratoriais dos pacientes. A análise estatística correlacionou os achados clínicos que incuíram fatores e preditores de risco, bem como transformação hemorrágica com os escores tomográficos que avaliam a isquemia cerebral. Resultados:o grupo com escore ASPECTS ≤7 apresentou significativamente maior uso de antiarrítmico, exclusão de trombólise, maior NIHSS, escala Rankin em 24h mais elevada e mais dias de internação quando comparado ao ASPECTS >7. Os pacientes com transformação hemorrágica apresentaram proporção significativamente maior de escore ASPECTS ≤ 7, mais do que um terço de acometimento do território da artéria cerebral média e AVC maior considerado pelo escore BASIS. Conclusão:os pacientes avaliados com AVC isquêmico cardioembólico que apresentaram transformação hemorrágica têm valores piores nos escores tomográficos de isquemia, com NHISS mais elevado e maior número de dias de internação. Houve uma correlação positiva entre o escore ASPECTS e os escores tomográficos regra de um terço e BASIS. / Introduction: although known worldwide, the correlation between tomographic cerebral ischemia evaluation scores and clinical outcome in patients with ischemic cerebral vascular accident (CVA), the evidences on patients with cardioembolic subtype are limited. Objective: evaluate and correlate the profile and clinical outcomes of patients with embolic subtype ischemic CVA with ischemia tomographic findings, according to tomographic scores. Methods: retrospective study of a patients group with cardioembolic subtype CVA according to TOAST classification, selected through a convenience sample from the patients that were treated at the cerebral vascular disease reference center emergency, (March 2014 to March 2015). These patients tomographic exams were evaluated by two observers (a radiologist with 10 years of expertise and another with 2 years of expertise in tomographic exams) trained in the assessment of tomographic scores related to encephalic ischemia alterations and blinded for the patients clinical and laboratorial data. The statistical analysis correlated the clinical findings, which included risk factors and predictors, as well as hemorrhagic transformation with the tomographic scores that evaluate cerebral ischemia. Results: groups with ASPECTS score ≤7 presented significantly higher use of antiarrhythmics, thrombolysis exclusion, higher NIHSS, higher 24 hours Rankin scale and more days of hospitalization when compared to ASPECTS >7. Patients with hemorrhagic transformation presented a significantly higher proportion of ASPECTS score ≤7. Conclusion: evaluated patients with cardioembolic ischemic CVA that had hemorrhagic transformation have worse tomographic ASPECTS score for ischemia, with higher NHISS and more hospitalization days. There was positive correlation between ASPECTS score and one third rule and BASIS tomographic scores.

This work introduces a combination of image processing and analysis methods that perform feature extraction, shape analysis and tomographic reconstruction of Electron Microscopy images. These have been implemented on images of the AIDS virus interacting with neutralizing molecules. The AIDS virus spike is the primary target of drug design as it is directly involved in infecting host cells. First, a fully automated technique is introduced that can extract sub-volumes of the AIDS virus spike and be used to build a statistical model without the need for any user supervision. Such an automatic feature extraction method can significantly enhance the overall process of shape analysis of the AIDS virus spike imaged through the electron microscope. Accurate models of the virus spike will help in the development of better drug design strategies. Secondly, a tomographic reconstruction method implemented using a shape based regularization technique is introduced. Spatial models of known features in the structure being reconstructed are integrated into the reconstruction process as regularizers. This regularization scheme is driven locally through shape information obtained from segmentation and compared with a known spatial model. This method shows reduced blurring, and an improvement in the resolution of the reconstructed volume was also measured. It performs better than popular current techniques and can be extended to other tomographic modalities. Improved Electron Tomography reconstructions will provide better structure elucidation and improved feature visualization, which can aid in solving key biological issues. / text

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Medical imaging has known great advances over the past decades to become a powerful tool for the clinical practice. It has led to the tremendous growth of interventional radiology, in which medical devices are inserted and manipulated under image guidance through the vascular system to the pathology location and then used to deliver the therapy. In these minimally-invasive procedures, X-ray guidance is carried out with C-arm systems through two-dimensional real-time projective low-dose images. More recently, three-dimensional visualization via tomographic acquisition has also become available. This work tackles tomographic reconstruction in the aforementioned context. More specifically, it deals with the correction of motion artifacts that originate from the temporal variations of the contrast-enhanced vessels and thus tackles a central aspect of tomography: data (angular) sampling. The compressed sensing theory identifies conditions under which subsampled data can be recovered through the minimization of a least-square data fidelity term combined with sparse constraints. Relying on this theory, an original reconstruction framework is proposed based on iterative filtered backprojection, proximal splitting, '1-minimization and homotopy. This framework is derived for integrating several spatial and temporal penalties. Such a strategy is shown to outperform the analytical filtered backprojection algorithm that is used in the current clinical practice by reducing motion and sampling artifacts in well-identified clinical cases, with focus on cerebral and abdominal imaging. The obtained results emphasize one of the key contributions of this work that is the importance of homotopy in addition to regularization, to provide much needed image quality improvement in the suggested domain of applicability.

Turbulence is ubiquitous in naturally-occurring and man-made flows. Despite its importance in scientific and engineering applications, the transition from smooth laminar flow to disorganized turbulent flow is poorly understood. In some cases, the transition can be understood in the context of linear stability theory, which predicts when the underlying laminar solution will become unstable as a parameter is varied. For a large class of flows, however, this approach fails spectacularly, with theory predicting that the laminar flow is stable but experiments and simulations showing the emergence of spatiotemporal complexity. In this dissertation, the direct or subcritical transition to turbulence in Taylor-Couette flow (i.e., the flow between independently rotating co-axial cylinders) is studied experimentally. Chapter 1 discusses different scenarios for the transition to turbulence and recent advances in understanding the subcritical transition within the framework of dynamical systems theory. Chapter 2 presents a comprehensive review of earlier investigations of linearly stable Taylor-Couette flow. Chapter 3 presents the first systematic study of long-lived super-transients in Taylor-Couette flow with the aim of determining the correct dynamical model for turbulent dynamics in the transitional regime. Chapter 4 presents the results of experiments regarding the stability of Taylor-Couette flow to finite-amplitude perturbations in the form of injection/suction of fluid from the test section. Chapter 5 presents numerical investigations of axisymmetric laminar states with realistic boundary conditions. Chapter 6 discusses in detail the implementation of time-resolved tomographic particle image velocimetry (PIV) in the Taylor-Couette geometry and presents preliminary tomographic PIV measurements of the growth of turbulent spots from finite-amplitude perturbations. The main results are summarized in Chapter 7.