Time-interleaved acquisition of modes: an analysis of SAR and image contrast implications

  • s the magnetic field strength and therefore the operational frequency in MRI are increased, the radiofrequency wavelength approaches the size of the human head/body, resulting in wave effects which cause signal decreases and dropouts. Especially, whole-body imaging at 7 T and higher is therefore challenging. Recently, an acquisition scheme called time-interleaved acquisition of modes has been proposed to tackle the inhomogeneity problems in high-field MRI. The basic premise is to excite two (or more) different Burn:x-wiley:07403194:media:MRM23081:tex2gif-stack-1 modes using static radiofrequency shimming in an interleaved acquisition, where the complementary radiofrequency patterns of the two modes can be exploited to improve overall signal homogeneity. In this work, the impact of time-interleaved acquisition of mode on image contrast as well as on time-averaged specific absorption rate is addressed in detail. Time-interleaved acquisition of mode is superior in Burn:x-wiley:07403194:media:MRM23081:tex2gif-stack-2 homogeneity compared with conventional radiofrequency shimming while being highly specific absorption rate efficient. Time-interleaved acquisition of modes can enable almost homogeneous high-field imaging throughout the entire field of view in PD, T2, and T2*-weighted imaging and, if a specified homogeneity criterion is met, in T1-weighted imaging as well.

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Metadaten
Author:S. Orzada, S. Maderwald, B. A. Poser, S. Johst, S. Kannengiesser, M. E. Ladd, Andreas Bitz
DOI:https://doi.org/10.1002/mrm.23081
ISSN:1522-2594
Parent Title (English):Magnetic Resonance in Medicine
Publisher:Wiley-Liss
Place of publication:New York
Document Type:Article
Language:English
Year of Completion:2012
Volume:67
Issue:4
First Page:1033
Last Page:1041
Link:https://doi.org/10.1002/mrm.23081
Zugriffsart:campus
Institutes:FH Aachen / Fachbereich Elektrotechnik und Informationstechnik
collections:Verlag / Wiley-Liss