Thesis (Ph. D.)--University of Hong Kong, 2010. / Includes bibliographical references (leaves 229-230). Also available in print.

Thesis (Ph.D)--Biomedical Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Hu, Xiaoping; Committee Member: Brummer, Marijn; Committee Member: Duong, Tim; Committee Member: Keilholz, Shella; Committee Member: Schumacher, Eric. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Thesis (Ph. D.)--Ohio State University, 2008. / Title from first page of PDF file. Includes bibliographical references (p. 106-111).

Thesis (Ph.D.)--Electrical and Computer Engineering, Georgia Institute of Technology, 2008. / Committee Chair: Skrinjar, Oskar; Committee Member: Oshinski, John; Committee Member: Tannenbaum, Allen; Committee Member: Vela, Patricio; Committee Member: Yezzi, Anthony

The semester thesis describes the basic principles of MRI, methods for measuring diffusion coefficients and creating DWI and DTI images. As a result a practical implementation of program was implemented in Matlab, based on theoretical knowledge of the problem.

No description available.

Traditional 1H lung imaging using MRI faces numerous challenges and difficulties due to low proton density and air-tissue susceptibility artifacts. New imaging techniques using inhaled xenon gas can overcome these challenges at the cost of lower signal to noise ratio. The signal to noise ratio determines reconstructed image quality and is an essential parameter in ensuring reliable results in MR imaging. The traditional RF surface coils used in MR imaging exhibit an inhomogeneous field, leading to reduced image quality. For the last few decades, fractal-shaped antennas have been used to optimize the performance of antennas for radiofrequency systems. Although widely used in radiofrequency identification systems, mobile phones, and other applications, fractal designs have yet to be fully researched in the MRI application space. The use of fractal geometries for RF coils may prove to be fruitful and thus prompts an investiga- tion as the main goal of this thesis. Preliminary simulation results and experimental validation results show that RF coils created using the Gosper and pentaflake offer improved signal to noise ratio and exhibit a more homogeneous field than that of a traditional circular surface coil. / Thesis / Master of Applied Science (MASc)

Introdução: Neurocisticercose (NCC) é a principal causa evitável de epilepsia adquirida no mundo. NCC, além de ser, a doença parasitária mais comum do SNC, representa um importante problema de saúde pública, especialmente em países em desenvolvimento. Estudos de neuroimagem são cruciais no diagnóstico e planejamento terapêutico da NCC. Apesar da ressonância magnética (RM) fornecer maior número e detalhe de informações sobre a doença, a tomografia computadorizada (TC) ainda é o método mais sensível na detecção de calcificação intracraniana, o achado radiológico mais comum da NCC. Objetivo: Comparar performance das sequências de RM ponderadas em suscetibilidade magnética na identificação de calcificações intracranianas em pacientes com NCC. Métodos: Estudo prospectivo, unicêntrico, no qual 57 indivíduos foram submetidos a TC e RM de crânio. Todos os indivíduos foram provenientes do Ambulatório de Doenças Infecciosas do Departamento de Neurologia do Hospital das Clínicas - Faculdade de Medicina da Universidade de São Paulo (HC-FMUSP), com diagnóstico confirmado de NCC. O protocolo de RM incluiu uma sequência convencional 2D gradiente eco (2D-GRE) e duas relativamente novas sequências de suscetibilidade magnética: susceptibilityweighted imaging (SWI) e principles of echo shifting with a train of observations (PRESTO). A TC foi considerada método padrão de referência. Dois neurorradiologistas, cegos para os dados clínicos e demais achados radiológicos, analisaram independentemente as sequências 2D-GRE, SWI e PRESTO quanto à presença, número e localizações de calcificações intracranianas atribuídas a NCC. Resultados: Foram identificadas, pela TC, 739 lesões calcificadas relacionadas a NCC em 50 dos 57 indivíduos incluídos no estudo. A média de lesões calcificadas por paciente foi de 12,9 (± 19,8). A médias de lesões encontradas pelas sequências de suscetibilidade magnética, obtido através da média dos resultados dos observadores, foi de 10,8 (± 17,5) para PRESTO, 10,6 (± 17,3) para SWI e 8,3 (± 13,6) para 2D-GRE. Neste quesito não houve diferença estaticamente significativa entre PRESTO e SWI (p = 0,359) e ambos foram superiores a 2D-GRE (p < 0,05). A concordância foi fraca a moderada, provavelmente devido ao alto número de lesões falso-positivas encontradas (490), das quais 53,9% representavam lesões relacionadas a NCC em estágios não calcificados. A sensibilidade e especificidade das sequências estudadas em identificar corretamente indivíduos com NCC em estágio calcificado foi respectivamente de 85% e 100% para 2D-GRE, 90% e 100% para SWI e 93% e 100% para PRESTO. Conclusão: As sequências SWI, PRESTO e 2D-GRE apresentam boa sensibilidade na identificação de lesões calcificadas em pacientes com NCC. As sequências SWI e PRESTO tiveram melhor performance do que 2D-GRE. Todas as sequências estudadas mostrarem-se apropriadas para identificar indivíduos com NCC no estágio de calcificação. Sequências ponderadas em suscetibilidade magnética podem ajudar no entendimento da história natural, fisiopatologia e achados de imagem da NCC / Background: Neurocysticercosis (NCC) is the main preventable cause of acquired epilepsy. NCC, besides being the most common parasitic disease of the CNS, is an important public health problem, mainly in developing countries. Neuroimaging studies are crucial in the diagnosis and therapeutic planning of NCC. Although magnetic resonance imaging (MRI) provides countless and more detailed information about the disease, computed tomography (CT) is still the most sensitive method for detecting intracranial calcification, the most common radiological finding of NCC. Purpose: To compare the diagnostic performance of susceptibility-weighted MRI sequences in identification of intracranial calcifications in patients with NCC. Methods: A prospective study with 57 subjects who underwent CT and MRI of the brain. All individuals came from Department of Neurology of the Hospital das Clínicas - Faculdade de Medicina da Universidade de São Paulo (HC-FMUSP), with a stablished diagnosis of NCC. The MRI protocol included a conventional 2D gradient echo sequence (2D-GRE) and two relatively new susceptibility-weighted sequences: susceptibility-weighted imaging (SWI) and principles of echo shifting with a train of observations (PRESTO). CT was considered the standard reference method. Two neuroradiologists, blinded to clinical data and other radiological findings, independently analyzed the 2D-GRE, SWI and PRESTO sequences on behalf to presence, number and sites of intracranial calcifications attributed to NCC. Results: A total of 739 NCC-related calcified lesions were identified by CT in 50 of the 57 subjects included in the study. The mean number of calcified lesions per patient was 12.9 (± 19.8). The mean number of lesions found by the susceptibility-weighted MRI sequences, obtained through the mean of the observers\' results, was 10.8 (± 17.5) for PRESTO, 10.6 (± 17.3) for SWI and 8.3 (± 13.6) for 2D-GRE. There was no statistically significant difference between PRESTO and SWI (p = 0.359) and both were superior to 2D-GRE (p < 0.05). The concordance was weak to moderate, probably due to the high number of false-positive lesions found (490), of which 53.9% represented NCC-related lesions in non-calcified stages. The sensitivity and specificity of the sequences studied in correctly identifying individuals with calcified NCC were 85% and 100% respectively for 2D-GRE, 90% and 100% for SWI and 93% and 100% for PRESTO. Conclusion: SWI, PRESTO and 2D-GRE sequences have good sensitivity in the identification of calcified lesions in patients with NCC. SWI and PRESTO performed better than 2DGRE. All sequences studied are suitable for identifying individuals with NCC in the calcified stage. The new susceptibility-weighted MRI sequences may help in understanding the natural history, pathophysiology and imaging findings of NCC

The non-invasive cardiovascular imaging modalities, cardiovascular magnetic resonance (CMR) and multi-detector computer tomography (MDCT) are playing an increasing role in both clinical and research settings. CMR is a unique imaging modality due to unsurpassed contrast between soft tissue structures that is non-invasive, does not use ionising radiation and is able to provide high-resolution information about cardiac anatomy, function, flow, perfusion, viability and metabolism. It has provided the gold standard in imaging in congenital heart disease. Recent advances in this technology have led to images of high spatial and temporal resolution that has made the characterisation of atheroma possible. While currently spatial resolution still limits its ability to characterise atheroma in native human coronary arteries in living patients, CMR imaging of the coronary arteries has future potential with further technological and sequence advances. MDCT has been used in clinical settings to measure of the amount of calcification in the coronary arteries with “coronary artery calcium scoring” of the coronary tree a surrogate marker of atherosclerosis. MDCT has also become the gold standard for angiographic imaging in most arterial beds such as the carotid and peripheral vascular systems. In the coronary arteries in particular, there have been major advances in the accuracy of coronary MDCT angiography, particularly with regards to its negative predictive value, although excessive calcification and blooming artefacts still limit the diagnostic accuracy of the technique for assessing stenotic severity. In this thesis, our aims were to address some specific novel areas advancing the utility of these imaging modalities in two major areas of interest, namely congenital heart disease and atheroma imaging. Our first step was to validate the accuracy and reproducibility of CMR, the main imaging modality we utilised. To achieve this, we assessed MR imaging of cardiac volumes and function in a normal adult Australian population with a specific focus on the reproducibility of the technique. In confirming that this technique in our hands is both accurate and reproducible, we would then be in a position to be able to confidently use this technique in our future chapters. However, more than this, we sought to establish some normal ranges for left and right atrial and ventricular parameters in our local population. This would be crucial background information for us to be able to make comparisons with future studies in patients with congenital heart disease. Having established our technique and reference ranges, we would then explore the two specific issues in the ensuing two chapters using CMR in one area of congenital heart disease, atrial septal defect. Atrial septal defect is the most common congenital heart defect first diagnosed in adults. The traditional method of assessment of these patients and for suitability for ASD closure involves semiinvasive investigation with transoesophageal echocardiography (TOE) for measurement of the defect size and atrial septal margins. MRI assessment of patients prior to percutaneous device closure compared to TOE assessment would provide information on the accuracy of TOE assessment and provide information of the utility of cardiac MRI as an alternative to TOE for the work-up of these patients prior to ASD closure. In our third original research chapter, we utilised CMR to understand the effects of percutaneous ASD closure on cardiac chamber volumes. We achieved this by assessing with cardiac MRI pre-closure and post-closure atrial and ventricular cardiac volumes. Longstanding right heart dilatation in the setting of an ASD may lead to complications including right heart failure, pulmonary hypertension and arrhythmia. Closure of the ASD should reduce right heart volumes by removing left-to-right shunting and lead to normalisation of ventricular volumes. The assessment of atrial volume changes with ASD closure may be important in furthering our understanding in its contribution to arrhythmia. Having assessed the ability of CMR to assess both the ASD dimensions, and therefore suitability for percutaneous closure, as well as the effects of ASD closure on cardiac chamber size, we look in the final two original research chapters to move to another area of research development with these highresolution imaging technologies, atherosclerosis imaging. Two particular areas we wished to focus on included the potential of high-resolution MR imaging to monitor effects of HDL infusion on atherosclerosis, and secondly to explore mechanisms behind limitations in MDCT imaging of atherosclerosis, specifically calcification and blooming artifacts. For assessing the effects of HDL infusion on atherosclerosis, we utilised a cholesterol-fed rabbit model of atherosclerosis. The abdominal aorta of the rabbit is comparable in size to the human coronary artery. Previous work with the rabbit model of atherosclerosis and magnetic resonance imaging of the aortic wall has shown that it can provide information about atherosclerotic composition as well as provide serial data of the arterial wall. While high intensity lipid-lowering with statins remains the first line management of at risk individuals, modest manipulations of serum HDL levels are associated with a significant impact on cardiovascular risk. Thus, we assessed the effect of HDL infusion and atorvastatin in a rabbit model of using MRI aortic atherosclerosis as the endpoint. In our fifth and final original research chapter, we assessed the accuracy of quantification of atherosclerotic calcification with MDCT in the carotid arteries of patients undergoing carotid endarterectomy, and sought to identify algorithms or techniques that may improve quantification of calcification. This would potentially lead to an improvement in the ability of MDCT techniques to quantify stenotic severity in coronary arteries that were calcified. To achieve these we utilised MDCT in vivo and in comparison with carotid endarterectomy specimen micro-CT. Importantly, as part of this study, we undertook a thorough assessment of reproducibility of these techniques. Thus, in summary, we have been able to confirm the accuracy and reproducibility of CMR and MDCT in the areas of a specific congenital defect (ASD) and atherosclerosis imaging, and utilised these techniques to advance our understanding of these disease states. This thesis identifies strengths and weaknesses of these techniques that will allow us to more appropriately use them for future purposes in cardiovascular disease. Future work directly stemming from this thesis has already begun, and now looks to address issues of whether CMR and MDCT may provide complimentary information about atherosclerotic lesions that may benefit outcomes in certain conditions. Specifically the work in this thesis has led to studies commencing in carotid atherosclerosis and saphenous vein graft atherosclerosis and using these imaging techniques to potentially predict adverse future outcomes. / Thesis (Ph.D.) -- University of Adelaide, School of Medical Sciences, 2008

The non-invasive cardiovascular imaging modalities, cardiovascular magnetic resonance (CMR) and multi-detector computer tomography (MDCT) are playing an increasing role in both clinical and research settings. CMR is a unique imaging modality due to unsurpassed contrast between soft tissue structures that is non-invasive, does not use ionising radiation and is able to provide high-resolution information about cardiac anatomy, function, flow, perfusion, viability and metabolism. It has provided the gold standard in imaging in congenital heart disease. Recent advances in this technology have led to images of high spatial and temporal resolution that has made the characterisation of atheroma possible. While currently spatial resolution still limits its ability to characterise atheroma in native human coronary arteries in living patients, CMR imaging of the coronary arteries has future potential with further technological and sequence advances. MDCT has been used in clinical settings to measure of the amount of calcification in the coronary arteries with “coronary artery calcium scoring” of the coronary tree a surrogate marker of atherosclerosis. MDCT has also become the gold standard for angiographic imaging in most arterial beds such as the carotid and peripheral vascular systems. In the coronary arteries in particular, there have been major advances in the accuracy of coronary MDCT angiography, particularly with regards to its negative predictive value, although excessive calcification and blooming artefacts still limit the diagnostic accuracy of the technique for assessing stenotic severity. In this thesis, our aims were to address some specific novel areas advancing the utility of these imaging modalities in two major areas of interest, namely congenital heart disease and atheroma imaging. Our first step was to validate the accuracy and reproducibility of CMR, the main imaging modality we utilised. To achieve this, we assessed MR imaging of cardiac volumes and function in a normal adult Australian population with a specific focus on the reproducibility of the technique. In confirming that this technique in our hands is both accurate and reproducible, we would then be in a position to be able to confidently use this technique in our future chapters. However, more than this, we sought to establish some normal ranges for left and right atrial and ventricular parameters in our local population. This would be crucial background information for us to be able to make comparisons with future studies in patients with congenital heart disease. Having established our technique and reference ranges, we would then explore the two specific issues in the ensuing two chapters using CMR in one area of congenital heart disease, atrial septal defect. Atrial septal defect is the most common congenital heart defect first diagnosed in adults. The traditional method of assessment of these patients and for suitability for ASD closure involves semiinvasive investigation with transoesophageal echocardiography (TOE) for measurement of the defect size and atrial septal margins. MRI assessment of patients prior to percutaneous device closure compared to TOE assessment would provide information on the accuracy of TOE assessment and provide information of the utility of cardiac MRI as an alternative to TOE for the work-up of these patients prior to ASD closure. In our third original research chapter, we utilised CMR to understand the effects of percutaneous ASD closure on cardiac chamber volumes. We achieved this by assessing with cardiac MRI pre-closure and post-closure atrial and ventricular cardiac volumes. Longstanding right heart dilatation in the setting of an ASD may lead to complications including right heart failure, pulmonary hypertension and arrhythmia. Closure of the ASD should reduce right heart volumes by removing left-to-right shunting and lead to normalisation of ventricular volumes. The assessment of atrial volume changes with ASD closure may be important in furthering our understanding in its contribution to arrhythmia. Having assessed the ability of CMR to assess both the ASD dimensions, and therefore suitability for percutaneous closure, as well as the effects of ASD closure on cardiac chamber size, we look in the final two original research chapters to move to another area of research development with these highresolution imaging technologies, atherosclerosis imaging. Two particular areas we wished to focus on included the potential of high-resolution MR imaging to monitor effects of HDL infusion on atherosclerosis, and secondly to explore mechanisms behind limitations in MDCT imaging of atherosclerosis, specifically calcification and blooming artifacts. For assessing the effects of HDL infusion on atherosclerosis, we utilised a cholesterol-fed rabbit model of atherosclerosis. The abdominal aorta of the rabbit is comparable in size to the human coronary artery. Previous work with the rabbit model of atherosclerosis and magnetic resonance imaging of the aortic wall has shown that it can provide information about atherosclerotic composition as well as provide serial data of the arterial wall. While high intensity lipid-lowering with statins remains the first line management of at risk individuals, modest manipulations of serum HDL levels are associated with a significant impact on cardiovascular risk. Thus, we assessed the effect of HDL infusion and atorvastatin in a rabbit model of using MRI aortic atherosclerosis as the endpoint. In our fifth and final original research chapter, we assessed the accuracy of quantification of atherosclerotic calcification with MDCT in the carotid arteries of patients undergoing carotid endarterectomy, and sought to identify algorithms or techniques that may improve quantification of calcification. This would potentially lead to an improvement in the ability of MDCT techniques to quantify stenotic severity in coronary arteries that were calcified. To achieve these we utilised MDCT in vivo and in comparison with carotid endarterectomy specimen micro-CT. Importantly, as part of this study, we undertook a thorough assessment of reproducibility of these techniques. Thus, in summary, we have been able to confirm the accuracy and reproducibility of CMR and MDCT in the areas of a specific congenital defect (ASD) and atherosclerosis imaging, and utilised these techniques to advance our understanding of these disease states. This thesis identifies strengths and weaknesses of these techniques that will allow us to more appropriately use them for future purposes in cardiovascular disease. Future work directly stemming from this thesis has already begun, and now looks to address issues of whether CMR and MDCT may provide complimentary information about atherosclerotic lesions that may benefit outcomes in certain conditions. Specifically the work in this thesis has led to studies commencing in carotid atherosclerosis and saphenous vein graft atherosclerosis and using these imaging techniques to potentially predict adverse future outcomes. / Thesis (Ph.D.) -- University of Adelaide, School of Medical Sciences, 2008