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Master's Dissertation
DOI
10.11606/D.76.1998.tde-18042007-095410
Document
Author
Full name
Eduardo Ribeiro de Azevêdo
Institute/School/College
Knowledge Area
Date of Defense
Published
São Carlos, 1998
Supervisor
Committee
Panepucci, Horacio Carlos (President)
Baffa Filho, Oswaldo
Castro Neto, Jarbas Caiado de
Title in Portuguese
Efeito do movimento em MRI e implementação das técnicas de Gradient Moment Nulling e pré-saturação especial na redução de artefatos relacionados ao movimento.
Keywords in Portuguese
Artefatos relacionados ao movimento
Compensação de efeitos do movimento
Imagens
Abstract in Portuguese
A proposta deste trabalho foi analisar os efeitos de movimento em imagens convencionais por ressonância magnética nuclear, bem como implementar e otimizar. as técnicas de "Gradient Moment Nulling" e Pré-Saturação Espacial, utilizadas para eliminação de artefatos relacionados ao movimento. Simulações numéricas foram utilizadas para a análise da influência do movimento dos spins nas imagens e para compreender as bases físicas das técnicas de "Gradient Moment Nulling" e Pré-saturação Espacial. Na técnica de "Gradient Moment Nulling" as amplitudes dos gradientes de compensação dependem do posicionamento dos mesmos na seqüência. Sendo assim, foram propostas algumas configurações para a seqüência e calculadas as amplitudes dos gradientes de compensação. A melhor configuração para a seqüência foi escolhida de modo a minimizar a amplitude dos gradientes. A técnica de "Gradient Moment Nulling" foi testada experimentalmente e os resultados mostraram sua eficacia na redução dos artefatos de "intravoxel dephasing" e misregistration". Na implementação da técnica de Pré-saturação Espacial foram utilizados pulsos de pré-saturação convencionais do tipo Sinc e as limitações na seqüência resultantes desta escolha foram analisadas experimentalmente e via simulações numéricas. A redução do efeitos de "flow related enhacement" e dos artefatos de "Aliasing" na imagens, foi alcançada com sucesso pela técnica de Pré-Saturação Espacial.
Title in English
Motion effects in magnetic resonance imaging and implementation of Gradient Moment Nulling and spatial presaturation for reducing motion related artifacts.
Keywords in English
Imaging
Motion effects compensation
Motion related artifacts
Abstract in English
The purpose of this work was to analyze the effects of motion in conventional Magnetic Resonance Imaging (MRI), and to implement and optimize the Gradient Moment Nulling and Spatial Presaturation techniques, which can be used to minimize the motion related artifacts. Numerical simulations, were used to analyze the influence of the motion on the image and to understand the physics of the above techniques. In the Gradient Moment Nulling method, the compensation gradients amplitudes depends on the their positions in the sequence. To analyze this, some configurations for the sequence were proposed and the corresponding gradients amplitude were calculated. The best configuration for the sequence was chosen to minimize the gradients amplitudes. The sequences were tested experimentally and the results proved their efficacy in reducing the intravoxel dephasing and flow blique misregistration artifacts. Conventional sinc pulse were used in the implementation of the Spatial Presaturation technique and the limitation of this choice was analyzed experimentally and by nurnerical simulation. The reduction of the flow related enhancement and "aliasing" artifacts, was successfully achieved by the Spatial Presaturation technique.
 
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Azevedo.pdf (4.78 Mbytes)
Publishing Date
2007-04-19
 
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