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Design and Evaluation of an RF Front-End for 9.4 T Human MRI

MPG-Autoren
http://pubman.mpdl.mpg.de/cone/persons/resource/persons84213

Shajan,  G
Department High-Field Magnetic Resonance, Max Planck Institute for Biological Cybernetics, Max Planck Society;
Department High-Field Magnetic Resonance, Max Planck Institute for Biological Cybernetics, Max Planck Society;

http://pubman.mpdl.mpg.de/cone/persons/resource/persons83973

Hoffmann,  J
Department High-Field Magnetic Resonance, Max Planck Institute for Biological Cybernetics, Max Planck Society;
Department High-Field Magnetic Resonance, Max Planck Institute for Biological Cybernetics, Max Planck Society;

http://pubman.mpdl.mpg.de/cone/persons/resource/persons83838

Budde,  J
Department High-Field Magnetic Resonance, Max Planck Institute for Biological Cybernetics, Max Planck Society;
Department High-Field Magnetic Resonance, Max Planck Institute for Biological Cybernetics, Max Planck Society;

http://pubman.mpdl.mpg.de/cone/persons/resource/persons84145

Pohmann,  R
Department High-Field Magnetic Resonance, Max Planck Institute for Biological Cybernetics, Max Planck Society;
Department High-Field Magnetic Resonance, Max Planck Institute for Biological Cybernetics, Max Planck Society;

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Zitation

Shajan, G., Hoffmann, J., Budde, J., Adriany G, Ugurbil, K., & Pohmann, R. (2011). Design and Evaluation of an RF Front-End for 9.4 T Human MRI. Magnetic Resonance in Medicine, 66(2), 594–602. doi:10.1002/mrm.22808.


Zitierlink: http://hdl.handle.net/11858/00-001M-0000-0013-BAB6-B
Zusammenfassung
At the field strength of 9.4 T, the highest field currently available for human MRI, the wavelength of the MR signals is significantly shorter than the size of the examined structures. Even more than at 7 T, constructive and destructive interferences cause strong inhomogeneities of the B1 field produced by a volume coil, causing shading over large parts of the image. Specialized radio frequency hardware and B1 management methods are required to obtain high-quality images that take full advantage of the high field strength. Here, the design and characteristics of a radio frequency front-end especially developed for proton imaging at 9.4 T are presented. In addition to a 16-channel transceiver array coil, capable of volume transmit mode and independent signal reception, it consists of custom built low noise preamplifiers and TR switches. Destructive interference patterns were eliminated, in virtually the entire brain, using a simple in situ radio frequency phase shimming technique. After mapping the Bmath image profile of each transmit channel, a numerical algorithm was used to calculate the appropriate transmit phase offsets needed to obtain a homogeneous excitation field over a user defined region. Between two and three phase settings are necessary to obtain homogeneous images over the entire brain.