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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

Comparative Clinical Efficacy of Computed Tomography, Ultrasonography, and Nuclear Medicine in Abdominal Application – A Clinical Trial

Boyle, Pierre B. 08 1900 (has links)
No description available.

Facial alveolar bone wall width: a cone beam computed tomography (CBCT) study in Asians

Zekry, Ahmed Khaled Ahmed Abdin. January 2012 (has links)
Background: The width of the facial alveolar bone wall is crucial for long term successful esthetic outcomes of implants immediately placed into extraction sockets. A threshold of 2 mm is recommended to minimize buccal vertical bone resorption. Aim: To assess the width of the facial alveolar bone wall using cone-beam computed tomography images (CBCT). Methods: Retrospective CBCT images were acquired from a representative sample of Asians using the i-CAT® classic system with a 0.4 mm voxel size. At random, 200 CBCT images were selected according to predefined criteria. The DICOM file was imported into the i-Cat Vision® software. In the panoramic screen, the middle of each tooth was selected and, in the sagittal window, the middle cross section was selected for performing the measurements using a computer. The vertical distance from the alveolar crest (BC) - CEJ was measured. The width of the facial alveolar bone wall was measured at three locations: 1, 3, and 5 mm apical to BC. Descriptive statistics, frequency analyses, and multi-level comparisons were performed. Results: The sample consisted of 74 males and 126 females (mean age of 37.2 years; range 17-82 years). A total of 3618 teeth were assessed. There was no significant difference between the values of right and left sides, or between genders. However, statistically significant differences were observed between age groups at all levels. The distance from CEJ-BC varied from 0.4 to 4mm, with an overall tendency to increase with age. The mean width of the facial alveolar bone wall at anterior teeth was 0.9 mm and increased towards posterior regions. Rarely, a width of 2 mm was yielded (0.6-1.8 % for anterior teeth, 0.7- 30.8 % for posterior teeth). At a 5mm distance from BC, minimal widths of facial alveolar bone were identified for the anterior teeth. The frequency of dehiscence ranged from 9.9- 51.6 % for anterior and 3.1- 53.6 % for posterior teeth, respectively. Conclusion and clinical implications: A thin facial alveolar bone wall was usually present in both jaws. Hence, for most patients, adjunctive bone augmentation may be needed when installing implants in areas of esthetic concern. / published_or_final_version / Dental Surgery / Master / Master of Dental Surgery

The characterization of retinal nerve fiber layer thickness in normal,high-tension and normal-tension glaucoma using optical coherencetomography

Mok, Kwok-hei., 莫國熙. January 2005 (has links)
published_or_final_version / abstract / Anatomy / Doctoral / Doctor of Philosophy

Micro-imaging characterization of mouse models of metastasis

Winkelmann, Christopher Todd, January 2005 (has links)
Thesis (Ph. D.)--University of Missouri-Columbia, 2005. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Vita. "December 2005" Includes bibliographical references.

Evaluation and verification of five different image reconstruction algorithms for electrical resistance tomography applications

Deba, Charlie Nindjou January 2016 (has links)
Thesis (MTech (Electrical Engineering))--Cape Peninsula University of Technology, 2016. / Tomography is the ability to internally visualise an opaque medium or a body, using different imaging techniques. Electrical Resistance Tomography (ERT) technique is a method commonly used in process tomography. It uses a non-intrusive resistance measurement between a set of electrodes attached on the circumference of a fixed cross-section with a given conductivity and permittivity distribution. ERT appears to be simple, low cost, safe and non-invasive. Despite the advantages of ERT, the reconstruction of the internal conductivity of the pipe still face a crucial challenges such as noise, a relatively low spatial resolution, as well as ill-posedness of the inverse problem when doing the image reconstruction using reconstruction algorithms. Although previous work showed the potential of various algorithms for the reconstruction of ERT tomograms, no full characterisation and comparison of different algorithms could be found for real flow situations. The ERT system was tested in the identification of different objects and fluid beds in a real time situation. The data collected from the measurements were then used for the image reconstruction using an algorithm developed by Time Long (One-step algorithm) and four EIDORS-based algorithms namely: Gauss-Newton algorithm with Laplace Prior (LP) and Gaussian prior (Automatic Hyper Parameter Selection (AHSP)), the Total Variation (TV) algorithm and the Conjugate Gradient (CG) algorithm. The performance of each algorithm was tested in different scenarios. The results obtained were then compared based on the quality and the accuracy of the images as well as the computational time of each algorithm. Firstly, reconstructed images were obtained using objects placed inside the ERT pipe test. Secondly, the algorithm performances were put to test in a level bed setup experiment and finally, the algorithm reconstructions were applied to the real flow situation, where different flow rates were applied. The results obtained were then analysed and compared.

Teoria e experimentação com metodos incrementais relaxados em tomografia por emissão / Theory and experimentation with relaxed incremental methods in emission tomography

Helou Neto, Elias Salomão 04 December 2005 (has links)
Orientador: Alvaro Rodolfo De Pierro / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Matematica, Estatistica e Computação Cientifica / Made available in DSpace on 2018-08-14T01:15:10Z (GMT). No. of bitstreams: 1 HelouNeto_EliasSalomao_M.pdf: 1733678 bytes, checksum: 44e680915a74638897d279b1d09a007f (MD5) Previous issue date: 2005 / Resumo: O principal assunto desta dissertação é a teoria e prratica em metodos iterativos incrementais relaxados para reconstrução estatística de imagens em Tomografia por Emissão de Positrons - PET. Especial atenção é dedicada ao estudo teorico dos algoritmos, com a apresentação de resultados novos sobre convergência com o parâmetro de relaxação variando dentre as subiterações e sobre a regularidade da sequência gerada por tais algoritmos no caso específico da função de log-verossimilhança que surge em PET. Alem disso, uma comparação experimental entre a qualidade da imagem obtida com metodos relaxados e não relaxados é efetuada / Abstract: The main subject of this dissertation is the theory and practice in iterative incremental relaxed methods for statistical image reconstruction in Positron Emission Tomograpy | PET. Special atention is drawn to the theoretical study of the algorithms, with the presentation of new results concerning convergence with a relaxation parameter wich is allowed to vary within the subiterations and about the regularity of the sequence generated by such algorithms in the specific case of the log-likelihood function that arises in PET. Furthermore, an experimental comparsion is made to test the quality of the image obtained with relaxed methods against those generated by non-relaxed ones / Mestrado / Mestre em Matemática Aplicada

Mathematical Problems of Thermoacoustic and Compton Camera Imaging

Georgieva-Hristova, Yulia Nekova 2010 August 1900 (has links)
The results presented in this dissertation concern two different types of tomographic imaging. The first part of the dissertation is devoted to the time reversal method for approximate reconstruction of images in thermoacoustic tomography. A thorough numerical study of the method is presented. Error estimates of the time reversal approximation are provided. In the second part of the dissertation a type of emission tomography, called Compton camera imaging is considered. The mathematical problem arising in Compton camera imaging is the inversion of the cone transform. We present three methods for inversion of this transform in two dimensions. Numerical examples of reconstructions by these methods are also provided. Lastly, we turn to a problem of significance in homeland security, namely the detection of geometrically small, low emission sources in the presence of a large background radiation. We consider the use of Compton type detectors for this purpose and describe an efficient method for detection of such sources. Numerical examples demonstrating this method are also provided.

Prevalence and factors associated with brown adipose tissue detected by 18F-FDG PET/CT in Hong Kong Chinese

Leung, Tsz-mei., 梁紫微. January 2012 (has links)
Brown adipose tissue (BAT) is a unique organ in existence in mammals. It can induce non-shivering thermogenesis to control body temperature and energy balance through the expression of uncoupling protein 1 (UCP1). In our study, we aimed to evaluate the prevalence of BAT, as detected by fluorine 18-fluorodeoxyglucose (18F-FDG) positron emission tomography combined computer tomography (PET/CT), in a Hong Kong Chinese population. We also assessed the influence of age and sex to BAT in Hong Kong Chinese population. We also determined the factors associated with it, in particular, its relationship with overweight and other metabolic disorders such as diabetes mellitus. We analyzed 1765 consecutive 18F-FDG PET-CT scans of 1442 Chinese for the presence of BAT. Comparison of the variables between positive and negative BAT scans was performed using Student’s t-test. The association between maximum value of standardized uptake value (SUVmax) and variables were explored by Spearman correlation. The predictors of observed BAT were analyzed by multiple logistic regression to determine the significant predictors of positive BAT. The relationship between the monthly numbers of subjects with BAT and the respective mean monthly outdoor temperature was evaluated by Pearson’s correlation co-efficient. P < 0.05 was considered to be statistically significant. Brown adipose tissue was detected in 66 out of 1442 subjects (4.6%). BAT was significantly more commonly found in younger (43.7±13.5 years old vs. 61.4±14.2 years old, P<0.001) and female (59% vs. 46%, P<0.05) subjects. BAT also existed more frequently in subjects with lower body mass index (BMI) (21.2±3.1 kg/m2 vs. 22.4±3.7 kg/m2, P<0.01) and lower blood glucose level (5.9±0.9 mmol/L vs. 6.4±1.6 mmol/L, P<0.01). Also, BAT was detected only in subjects with no history of diabetes meallitus (DM) (0 vs. 10%, P<0.01). Moreover, lower outdoor temperature (21.6±4.6。C vs. 23.4±4.7。C, P<0.005) resulted in higher prevalence of detected BAT. In the multiple logistic regression test, age and mean monthly temperatures were the significant independent predictors of the presence of BAT (P< 0.001 and P=0.001). Age was also significantly correlated to SUVmax (P< 0.001). The monthly prevalence of positive BAT correlated negatively with mean monthly temperature by Pearson’s correlation (r = -0.79; P<0.01). To summarize, BAT was more commonly found in young, female subjects with lower BMI and blood glucose levels, and non-diabetes subjects. Age was the most important factor associated with the prevalence of BAT in humans. Lower outdoor temperature in winter can increase the prevalence of BAT even in Hong Kong’s sub-tropical climates. Also, there was an association of BAT with normal BMI (<=23) and lower blood sugar levels supporting the notion that BAT may potentially be a therapeutic target for obesity and diabetes. / published_or_final_version / Diagnostic Radiology / Master / Master of Philosophy

The role of computed tomography volumetry in the assessment of advanced lung cancer and oesophageal cancer

Yip, Tsz-chung., 葉子仲. January 2002 (has links)
published_or_final_version / abstract / toc / Diagnostic Radiology / Master / Master of Philosophy

Spatio-temporal registration of dynamic PET data

Jiao, Jieqing January 2014 (has links)
Medical imaging plays an essential role in current clinical research and practice. Among the wealth of available imaging modalities, Positron Tomography Emission (PET) reveals functional processes in vivo by providing information on the interaction between a biological target and its tracer at the molecular level. A time series of PET images obtained from a dynamic scan depicts the spatio-temporal distribution of the PET tracer. Analysing the dynamic PET data then enables the quantification of the functional processes of interest for disease understanding and drug development. Given the time duration of a dynamic PET scan, which is usually 1-2 hours, any subject motion inevitably corrupts the tissue-tovoxel mapping during PET imaging, resulting in an unreliable analysis of the data for clinical decision making. Image registration has been applied to perform motion correction on misaligned dynamic PET frames, however, the current methods are solely based on spatial similarity. By ignoring the temporal changes due to PET tracer kinetics they can lead to inaccurate registration. In this thesis, a spatio-temporal registration framework of dynamic PET data is developed to overcome such limits. There are three scientific contributions made in this thesis. Firstly, the likelihood of dynamic PET data is formulated based on the generative model with both tracer kinetics and subject motion, providing a novel objective function. Secondly, the solution to the optimisation based on the generic plasma-input model is given, leading to the availability of a variety of biological targets. Thirdly, reference-input models are also incorporated to avoid blood sampling and thus extend the coverage of PET studies of the proposed framework. In the simulation-based validation, the proposed method achieves sub-voxel accuracy and its impact on clinical studies is evaluated on dopamine receptor data from an occupancy study, as well as breast cancer data from a reproducibility study. By successfully eliminating the motion artifacts as shown by visual inspection, the proposed method reduces the variability in clinical PET data and improves the confidence of deriving outcome measures on a study level. The motion correction algorithms developed in this thesis do not require any additional computational resources for a PET research centre, and they facilitate cost reduction by eliminating the need of acquiring extra PET scans in cases of motion corruption.

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