Combination of a multimode antenna and TIAMO for traveling-wave imaging at 9.4 Tesla.
OBJECTIVE
To investigate the performance of a multimode antenna combined with time-interleaved acquisition of modes (TIAMO) for improved (1)H 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 B1+ patterns ( B1,RSS+). 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 B1,RSS+ 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.


CONCLUSIONS
Despite the limited number of channels, a remote three-port antenna combined with TIAMO represents an easily implementable setup to achieve void-free (1)H images from the entire brain at 9.4 T, which can be used for anatomical localization and B0 shimming.
High-Field Magnetic Resonance Center, Max Planck Institute for Biological Cybernetics, Tübingen, Germany.|Graduate School of Neural and Behavioural Sciences, Tübingen, Germany.
Jens
J
Hoffmann
High-Field Magnetic Resonance Center, Max Planck Institute for Biological Cybernetics, Tübingen, Germany.|Department for Biomedical Magnetic Resonance, University of Tübingen, Tübingen, Germany.
Christian
C
Mirkes
High-Field Magnetic Resonance Center, Max Planck Institute for Biological Cybernetics, Tübingen, Germany.
G
G
Shajan
High-Field Magnetic Resonance Center, Max Planck Institute for Biological Cybernetics, Tübingen, Germany.|Department for Biomedical Magnetic Resonance, University of Tübingen, Tübingen, Germany.
Klaus
K
Scheffler
High-Field Magnetic Resonance Center, Max Planck Institute for Biological Cybernetics, Tübingen, Germany.
Rolf
http://orcid.org/0000-0002-6137-9590
R
Pohmann
D017076:Computer-Aided Design; D004867:Equipment Design; D019544:Equipment Failure Analysis; D006801:Humans; D007089:Image Enhancement / Q000295:instrumentation*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D019047:Phantoms, Imaging; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D018511:Systems Integration; D014159:Transducers
9.4 Tesla; TIAMO; multimode excitation; traveling-wave imaging; ultrahigh field