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Master's Dissertation
DOI
10.11606/D.54.1994.tde-06122013-143859
Document
Author
Full name
Bernd Uwe Foerster
Institute/School/College
Knowledge Area
Date of Defense
Published
São Carlos, 1994
Supervisor
Committee
Tannus, Alberto (President)
Barberis, Gaston Eduardo
Bonagamba, Tito Jose
Title in Portuguese
Técnicas de aquisição rápida em tomografia por ressonância magnética nuclear
Keywords in Portuguese
Aquisição Rápida
Estado Estacionário
Imagens por Ressonancia Magnética
Abstract in Portuguese
Neste trabalho apresentamos e comparamos diferentes técnicas de tomografia bidimensional por RMN implementados num sistema de tomografia de campo magnético ultra-baixo (O.05T). A partir da seqüência convencional "Spin Echo" (SE), utilizada rotineiramente, implementamos a seqüência "Gradient Recalled Echo" (GRE) e duas seqüências que utilizam o principio de Steady-State Free Precession (SSFP), sendo "Fast Low Angle Shot" (FLASH) e "Fast Acquisition Double Echo" (FADE). Com as seqüências de SSFP conseguimos diminuir drasticamente a duração de um exame de tomografia convencional (seqüência SE). A seqüência FADE ainda permite adquirir duas imagens com contrastes claramente diferentes sem aumentar significativamente a duração do exame. Desenvolvemos procedimentos de calibração indispensáveis para as técnicas de SSFP que também melhoraram a relação sinal ruído de 15 por cento na técnica SE . Analisamos teórica e experimentalmente o comportamento do contraste das seqüências apresentadas. Fizemos ainda uma serie de imagens de um phantom e da cabeça de um voluntário com as diferentes seqüências e sugerimos algumas combinações dos parâmetros (protocolos) como tempo de repetição, tempo ao eco e angulo de excitação. Um destes protocolos esta sendo testado em casos clínicos para comparar a utilidade das seqüências apresentadas no diagnóstico medico. Com este trabalho ganhamos uma experiência na utilização de técnicas rápidas indispensáveis para a elaboração de uma metodologia para obter imagens tridimensionais
Title in English
Magnetic resonance tomography fast acquisition techniques
Keywords in English
Fast acquisition
Magnetic resonance imaging
Steady state
Abstract in English
In this work we present and compare different techniques for bidimensional tomography in NMR which were implemented on a ultra low magnetic field (O.05T) tomographic system. Based on the conventional spin echo pulse sequence (SE), which is routinely used, we implemented the gradient recalled echo (GRE) pulse sequence and two sequences that use the principle of Steady-State Free Precession (SSFP) being "Fast Low Angle Shot" (FLASH) and "Fast Acquisition Double Echo" (FADE). With the SSFP sequences we shorten drastically the duration of the conventional SE tomography sequence. Besides this the FADE sequence gives two images with clearly different contrast without extending significantly the duration of the experiment. Needed for the SSFP techniques, we developed calibration procedures, which improved as well the SE sequence signal to noise ratio of about 15 percent. We analyzed theoretically and experimentally the behavior of the contrast of the presented sequences. Moreover we acquired various images of a phantom and the human brain of a normal volunteer using the different sequences and proposed some combinations of the parameters (protocols) repetition time, time to echo and flip angle. One of these protocols is being tested in clinical cases to compare the usefulness of the presented techniques for medical diagnostic. With this work we gained a wide experience in using SSFP techniques that will be indispensable in the elaboration of three-dimensional tomography methodologies
 
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Publishing Date
2013-12-09
 
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