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In this study, RF coil geometries are designed for MRI applications using inhomogeneous main magnetic fields. The current density distributions that can produce the desired RF magnetic field characteristics are obtained on predefined cubic, cylindrical and planar surfaces and Tikhonov, CGLS, TSVD and Rutisbauer regularization methods are applied to match the desired and generated magnetic fields. The conductor paths, which can produce the current density distribution calculated for each surface selection and regularization technique, are determined using stream functions. The magnetic fields generated by the current distributions are calculated and the error percentages between the desired and generated magnetic fields are found. Optimum conductor paths that are going to be produced on cubic, cylindrical and planar surfaces and the required regularization method are determined on the basis of error percentages and realizability of the conductor paths. The optimum conductor path calculated for the planar coil is realized and in the measurement done by LakeShore 3-Channel Gaussmeter, an average error percentage of 11 is obtained between the theoretical and measured magnetic field. The inductance values of the realized RF coil are measured / the tuning and matching capacitance values are calculated and the frequency characteristics of the system is tested using Electronic Workbench 5.1. The quality factor value of the tested system is found to be 162.5, which corresponds to a bandwidth of 39,2 KHz at 6,387 MHz (operating frequency of METU MRI system). The techniques suggested in this study can be used in order to design and realize RF coils on prede&macr / ned arbitrary surfaces for inhomogeneous main magnetic fields. In addition, a hand held MRI device can be manufactured which uses a low cost permanent magnet to provide a magnetic field and generates the required RF field with the designed RF coil using the techniques suggested in this study.

Made available in DSpace on 2016-04-18T21:39:44Z (GMT). No. of bitstreams: 8 Valderez de Almeida Donzelli1.pdf: 2513417 bytes, checksum: 39732bb9cc22ff6c7d8b226a01c7fbb3 (MD5) Valderez de Almeida Donzelli2.pdf: 3170782 bytes, checksum: 5bec891551d4e67354a5cb930c33b44a (MD5) Valderez de Almeida Donzelli3.pdf: 3092150 bytes, checksum: d7f43803b4c7e0a2393cc4faa9f5db7f (MD5) Valderez de Almeida Donzelli4.pdf: 3808963 bytes, checksum: 80f16c085a45c26b9ee5aa087fecb887 (MD5) Valderez de Almeida Donzelli5.pdf: 2761540 bytes, checksum: 6b89bedf4c70eb288d052ad64721157d (MD5) Valderez de Almeida Donzelli6.pdf: 3455846 bytes, checksum: 29fde75066aafda6127105ade4238eca (MD5) Valderez de Almeida Donzelli7.pdf: 3390797 bytes, checksum: bea566456cc4e0ff6ddf3fffb614b78a (MD5) Valderez de Almeida Donzelli8.pdf: 2402725 bytes, checksum: 1447647552515388643c1d9896a3803b (MD5) Previous issue date: 2011-08-05 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The technology environment in the broadcast area using analog technology was defined and did not offer a great research interest, in specific topics related to development of the transmitting antenna for broadcast television. With the implementation of the transmission system employing digital technology, which adds as main news the possibility of mobility and portability of the receiving system, the interest in studies and researches returned, showing one of the main themes to be developed using circular polarization or elliptical compared with horizontal polarization, that was most used by broadcasters. Given this new scenario and the need for evaluation by a scientific methodology of the radiating system in the transmission station performance, goals were established that define the scope for this research: to analyze the influence of the radiating system depending on the desired coverage area and the reception possibilities internal fixed , external fixed, portable and mobile, considering the diversity specific propagation environment of the region studied due to topographical and environmental condition. The criteria to be used will be the theoretical propagation prediction and field survey of the signals received which will provide data for the analysis of variables that influence the behavior of the transmission system, considering the location and technical characteristics of the main transmission station installation and different polarization of the radiating system configurations in horizontal, vertical and elliptical. / O cenário tecnológico na área de transmissão empregando tecnologia analógica estava bem segmentado e não oferecia um ambiente de grande interesse em pesquisas específicas para desenvolvimentos de temas relacionados a antena de transmissão para televisão aberta. Com a implantação do sistema de transmissão empregando a tecnologia digital, que agrega como principal novidade a possibilidade de mobilidade e portabilidade do sistema de recepção , o interesse nos estudos e pesquisas retomou, apresentando como um dos principais temas a serem desenvolvidos a utilização de polarização circular ou elíptica comparada com a polarização horizontal, que era a mais utilizada pela emissoras. Tendo em vista este novo cenário e a necessidade de avaliação por meio de uma metodologia científica do comportamento do sistema irradiante de transmissão no resultado no desempenho da estação transmissora, foram estabelecidas as metas que definem o escopo para este trabalho: analisar a influência do tipo de sistema irradiante em função da área de cobertura desejada e das possibilidades de recepção fixa interna, fixa externa, portátil e móvel, frente às diversidades específicas do ambiente de propagação da região estudada devido às condições topográficas e ambientais. Os critérios a serem empregados serão os teóricos de predição de propagação e prático de levantamento de campo dos sinais recebidos os quais irão fornecer dados para a análise das variáveis que influenciam no comportamento do sistema de transmissão, considerando o local e as características técnicas de instalação da estação de transmissão principal e variando a polarização do sistema irradiante nas configurações horizontal, vertical e elíptica.