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Combination of a multimode antenna and TIAMO for traveling-wave imaging at 9.4 Tesla

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

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

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

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Hoffmann, J., Mirkes, C., Shajan, G., Scheffler, K., & Pohmann, R. (2016). Combination of a multimode antenna and TIAMO for traveling-wave imaging at 9.4 Tesla. Magnetic Resonance in Medicine, 75(1), 452-462. doi:10.1002/mrm.25614.


Cite as: http://hdl.handle.net/21.11116/0000-0000-7A3A-7
Abstract
Purpose To investigate the performance of a multimode antenna combined with time-interleaved acquisition of modes (TIAMO) for improved 1H image homogeneity as compared to conventional traveling-wave imaging in the human brain at 9.4 Tesla (T). Methods An adjustable three-port antenna was built to stimulate the propagation of three basic waveguide modes within a 9.4 T scanner bore. For TIAMO, two time-interleaved acquisitions using different linear combinations of these modes were optimized to achieve a homogeneous rooted sum-of-squares combination of their inline image patterns ( inline image). The antenna's transmit and receive performance, as well as local specific absorption rate, were analyzed using experiments and numerical simulations. Results The optimized TIAMO inline image combination was superior to radiofrequency shimming. Across the entire brain, it improved the homogeneity of the excitation field by a factor of two and its maximum-to-minimum ratio by almost a factor of five as compared to the circularly polarized mode. The two-fold increase in “virtual” receive channels enhanced the parallel imaging performance and enabled the use of higher acceleration factors. Conclusion Despite the limited number of channels, a remote three-port antenna combined with TIAMO represents an easily implementable setup to achieve void-free 1H images from the entire brain at 9.4 T, which can be used for anatomical localization and B0 shimming.