Traveling-Wave RF Shimming and Parallel MRI
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Date
2011-07
Publication Type
Journal Article
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yes
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Abstract
At sufficiently high Larmor frequencies, traveling electromagnetic waves along a magnet bore can be used for remote magnetic resonance excitation and detection, effectively using the bore as a waveguide. So far, this approach has relied only on the lowest waveguide modes and thus has not supported multiple-channel operation for radiofrequency shimming and parallel imaging. In this work, this limitation is addressed by establishing a larger number of propagating modes and tapping their spatial field diversity with multiple waveguide ports. The number of available modes is increased by loading with dielectric inserts; the ports are implemented by stub and loop couplers at the end of a waveguide extension. The resulting traveling-wave array, operated at 298 MHz in a 7T whole-body magnet, is shown to enable radiofrequency shimming as well as parallel imaging with commonly used acceleration factors. The last part of the study concerns the amount of dielectric loading that is required. For the given Larmor frequency and bore dimensions, it is found that rather few water-filled inserts, occupying ∼5% of the bore cross-section, are sufficient for effective parallel imaging.
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published
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Journal / series
Volume
66 (1)
Pages / Article No.
290 - 300
Publisher
Wiley-Blackwell
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Subject
High-field MRI; Circular waveguide; Propagating mode; Cut-off frequency; Dielectric filling; SENSE
Organisational unit
03628 - Prüssmann, Klaas P. / Prüssmann, Klaas P.
03472 - Professur für Feldtheorie (ehemalig)