Hoffmann J, Mirkes C, Shajan G, Scheffler K, Pohmann R. Combination of a multimode antenna and TIAMO for traveling-wave imaging at 9.4 Tesla.
Magn Reson Med 2015;
75:452-62. [PMID:
25732895 DOI:
10.1002/mrm.25614]
[Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2014] [Revised: 12/15/2014] [Accepted: 12/18/2014] [Indexed: 11/09/2022]
Abstract
PURPOSE
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.
CONCLUSION
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.
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