INTRODUCTION: HIV/AIDS is a global health problem, with Sub-Saharan Africa the most affected. “Neuro-AIDS” refers to the extensive neuropathological manifestations of the disease. Neuroimaging of the HIV-infected individual plays a fundamental role in their work-up. Limited resources, however, drive the development of imaging protocols based on clinical signs. ‘Confusion’ may or may not represent a significant presenting sign and needs to be investigated, as it is the basis of referral of a significant number of patients for CT scanning. AIM: To determine the frequency of positive findings of head CT in HIV-infected adults presenting with confusion with/without associated neurology, and correlate them with the degree of immunosuppression, presence of CSF abnormality and their ARV therapy status. METHOD: CT brain scans of adult patients, who were HIV-positive and presented with confusion in Johannesburg, Gauteng, were retrospectively reviewed. The neurological status, CD4 counts, LP results and their ARV therapy status were documented. RESULTS: 30% of our HIV-infected patients presented with confusion. There were 156 patients who were included. CT scans were abnormal in 81%. We found that ‘associated neurology’ was a weak predictor for abnormal CT, making it a poor screening tool. A positive LP was predictive of infection (p=0.04 for focal infection, p=0.03 for infected surface collection) and infarction (p<0.01) on CT. CD4 count, LP results and ARV therapy were found to be abnormal in the majority of patients. CONCLUSIONS: CT was abnormal in the majority of HIV-infected patients presenting with confusion. Neurology was an unreliable clinical indicator. A positive LP was a good predictor for CT evidence of infection and infarction. The clinical parameters such as CD4 counts, LP results and ARV therapy, were abnormal in the majority of patients. If any of these parameters are abnormal in a patient with a normal CT, we believe this should motivate for further imaging with MRI.

Thesis (doctoral)--Karolinska Institutet, Stockholm, 1988. / Extra t.p. with thesis statement inserted. Includes bibliographical references.

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

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

INTRODUÇÃO: A gordura visceral abdominal tem sido associada com os fatores de risco cardiovasculares e com a doença arterial coronária (DAC). A maior parte dos estudos delineados para avaliar o risco atribuído à distribuição da gordura corporal utilizaram as medidas antropométricas para estimar a gordura visceral. Entretanto, quando comparada com as medidas antropométricas tradicionais (circunferência do quadril e relação das medidas da cintura e quadril), a gordura visceral avaliada pela tomografia computadorizada (TC) foi mais intensamente associada aos fatores de risco para DAC. A angiografia por TC com múltiplos detectores é um método diagnóstico em ascensão, permitindo a detecção de DAC obstrutiva e não obstrutiva, acrescentando informação para a estratificação de risco cardiovascular. O objetivo desse estudo foi avaliar a associação entre DAC e as medidas de adiposidade por métodos clínicos e tomográficos. MÉTODOS: Nós avaliamos prospectivamente 125 indivíduos consecutivos (57% eram homens, idade média de 56 ± 12 anos) referenciados para realizar angiografia coronária por TC. As variáveis clínicas e laboratoriais foram determinadas e tomografias cardíacas e abdominais foram realizadas em um tomógrafo com 64 fileiras de detectores. A DAC foi definida pela presença de qualquer placa coronária, calcificada ou não, identificada pela angiografia por TC. As artérias coronárias foram classificadas de acordo com a presença ou não de estenoses significativas (obstrução do diâmetro luminal 50%). As calcificações coronárias foram determinadas pelo escore de cálcio. As medidas de gordura visceral e subcutâneas foram realizadas em diferentes níveis do espaço intervertebral. RESULTADOS: A angiografia por TC detectou DAC em 70 participantes (56%) e nenhuma associação foi encontrada com as medidas antropométricas usuais (circunferências de cintura e quadril e índice de massa corpórea). Entretanto, as medidas das áreas de gordura visceral abdominal (GVA) foram significativamente associadas ao diagnóstico de DAC. As médias das áreas de GVA no espaço intervertebral L1-T12 (GVA L1-T12) e L4-L5 (GVA L4-L5) foram 151,2 cm2 e 167,2 cm2, respectivamente. Valores de GVA L1-T12 145 cm2 apresentaram odds ratio de 2,85 (1,3 6,26, IC95%) para o diagnóstico de DAC e a GVA L4-L5 150 cm2 apresentou odds ratio de 2,87 (1,31 6,3, IC 95%) para DAC. As medidas de adiposidade não mostraram associação com o grau de estenose coronária, nem com a presença de calcificações coronárias identificadas pelo escore de cálcio. A análise multivariada determinou a idade e a GVAL1-T12 como as únicas variáveis independentemente associadas ao diagnóstico de DAC. CONCLUSÃO: A gordura visceral avaliada pela TC é um marcador independente de DAC diagnosticada pela angiografia coronária por TC. A avaliação da gordura visceral pela TC em diferentes sítios abdominais foi fortemente associada à DAC, e não se associou às tradicionais variáveis antropométricas e clínicas utilizadas para estimar o risco cardiovascular. A utilização das medidas de adiposidade pela TC na prática clínica pode agregar valor à estratificação de risco da DAC / INTRODUCTION: Visceral abdominal fat has been associated with cardiovascular risk factors and coronary artery disease (CAD). Visceral fat is frequently estimated using anthropometric measurements, but computed tomography (CT) studies have shown stronger association with CAD risk than anthropometric variables (waist circumference, waist-to-hip ratio). CT angiography is an emerging technology allowing detection of both obstructive and nonobstructive CAD adding information to clinical risk stratification. The aim of this study was to evaluate the association between CAD and adiposity measurements assessed clinically and by CT. METHODS: We prospectively evaluated 125 consecutive subjects (57% men, age 56.0 ± 12 years) referred to perform CT angiography. Clinical and laboratory data were determined. Cardiac CT and abdominal CT were performed in a 64- slice scanner. CAD was defined as the presence of any plaque detected by CT angiography and stenosis were graded as significant (greater than 50% of luminal narrowing) or nonsiginificant (less than 50%). The presence of coronary calcification was determined by calcium score. Visceral and subcutaneous adiposity measurements were determined at different intervertebral levels. RESULTS: CT angiography detected CAD in 70 (56%) subjects, and no association was found with usual anthropometric adiposity measurements. Nevertheless CT visceral fat area (VFA) was significantly associated to CAD. The mean VFA at the intervertebral locations T12-L1 (VFA L1-T12) and L4-L5 (VFA L4-L5) were 151.2 cm2 and 167.2 cm2, respectively. VFA L1-T12 values 145 cm2 had an odds ratio of 2.85 (95% CI - 1.30 6.26) to CAD and VFA L4-L5 150 cm2 had a 2.87-fold (95% CI - 1.31-6.30) CAD risk. Adiposity measurement was not related to stenosis severity and neither to the presence of coronary calcification. The multivariate analysis determined age and VFA L1-T12 as the only independent variables associated to CAD. CONCLUSION: Visceral fat as assessed by CT angiography is an independent marker of CAD. VFA in different abdominal sites was strongly related to CAD but this relation was not found using anthropometric measurements and clinical variables. The use of these CT adiposity measurements in the clinical practice may improve the risk stratification to CAD

In this thesis we present new ideas and mathematical insights in the field of Compton Scattering Tomography (CST), an X-ray and gamma ray imaging technique which uses Compton scattered data to reconstruct an electron density of the target. This is an area not considered extensively in the literature, with only two dimensional gamma ray (monochromatic source) CST problems being analysed thus far. The analytic treatment of the polychromatic source case is left untouched and while there are three dimensional acquisition geometries in CST which consider the reconstruction of gamma ray source intensities, an explicit three dimensional electron density reconstruction from Compton scatter data is yet to be obtained. Noting this gap in the literature, we aim to make new and significant advancements in CST, in particular in answering the questions of the three dimensional density reconstruction and polychromatic source problem. Specifically we provide novel and conclusive results on the stability and uniqueness properties of two and three dimensional inverse problems in CST through an analysis of a disc transform and a generalized spindle torus transform. In the final chapter of the thesis we give a novel analysis of the stability of a spindle torus transform from a microlocal perspective. The practical application of our inversion methods to fields in X-ray and gamma ray imaging are also assessed through simulation work.

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

The Computer Tomography (CT) scanned images are very important for the Treatment Planning System (TPS) to provide the electron density of the different types of tissues that the radiation penetrates in the path to the tumor to be treated. This electron density is converted to an attenuation coefficient, which varies with tissue for each structure and even varies by the tissue volume. The purpose of this research is to evaluate the CT numbers, and convert them into relative electron densities. Twenty-five patients’ data and CT numbers were evaluated in the CT scanner and in Eclipse and were converted into relative electron density and compared with each other. The differences between the relative electron density in the Eclipse was found to be from 0 up to 6% between tissue equivalent materials, the final result for all equivalent tissue materials was about 2%. For the patients’ data, the percentage difference of CT number versus electron density was found to be high for high relative electron density organs, namely the final average result for the spine was 8%, less for pelvis, and less for rib while for the other organs it was even less. The very lowest was 0.3% compared with 1% which is acceptable for clinical standards. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2019. / FAU Electronic Theses and Dissertations Collection

Thesis--University of Oklahoma. / Bibliography: leaves 97-101.