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Simultaneous mapping of water shift and B 1 (WASABI)—Application to field‐Inhomogeneity correction of CEST MRI data
Author(s) -
Schuenke Patrick,
Windschuh Johannes,
Roeloffs Volkert,
Ladd Mark E.,
Bachert Peter,
Zaiss Moritz
Publication year - 2017
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.26133
Subject(s) - field (mathematics) , nuclear magnetic resonance , computer science , physics , chemistry , mathematics , pure mathematics
Purpose Together with the development of MRI contrasts that are inherently small in their magnitude, increased magnetic field accuracy is also required. Hence, mapping of the static magnetic field (B 0 ) and the excitation field (B 1 ) is not only important to feedback shim algorithms, but also for postprocess contrast‐correction procedures. Methods A novel field‐inhomogeneity mapping method is presented that allows simultaneous mapping of the water shift and B 1 (WASABI) using an off‐resonant rectangular preparation pulse. The induced Rabi oscillations lead to a sinc‐like spectrum in the frequency‐offset dimension and allow for determination of B 0 by its symmetry axis and of B 1 by its oscillation frequency. Results Stability of the WASABI method with regard to the influences of T 1 , T 2 , magnetization transfer, and repetition time was investigated and its convergence interval was verified. B 0 and B 1 maps obtained simultaneously by means of WASABI in the human brain at 3 T and 7 T can compete well with maps obtained by standard methods. Finally, the method was applied successfully for B 0 and B 1 correction of chemical exchange saturation transfer MRI (CEST‐MRI) data of the human brain. Conclusion The proposed WASABI method yields a novel simultaneous B 0 and B 1 mapping within 1 min that is robust and easy to implement. Magn Reson Med 77:571–580, 2017. © 2016 International Society for Magnetic Resonance in Medicine