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SA2RAGE: A new sequence for fast B 1 + ‐mapping
Author(s) -
Eggenschwiler Florent,
Kober Tobias,
Magill Arthur W.,
Gruetter Rolf,
Marques José P.
Publication year - 2012
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.23145
Subject(s) - flip angle , imaging phantom , sequence (biology) , physics , specific absorption rate , computer science , field (mathematics) , magnetic field , nuclear magnetic resonance , algorithm , optics , mathematics , chemistry , magnetic resonance imaging , telecommunications , medicine , biochemistry , quantum mechanics , pure mathematics , antenna (radio) , radiology
At high magnetic field strengths (≥3T), the radiofrequency wavelength used in MRI is of the same order of magnitude of (or smaller than) the typical sample size, making transmit magnetic field ( B 1 + ) inhomogeneities more prominent. Methods such as radiofrequency‐shimming and transmit SENSE have been proposed to mitigate these undesirable effects. A prerequisite for such approaches is an accurate and rapid characterization of the B 1 +field in the organ of interest. In this work, a new phase‐sensitive three‐dimensional B 1 + ‐mapping technique is introduced that allows the acquisition of a 64 × 64 × 8 B 1 + ‐map in ∼20 s, yielding an accurate mapping of the relative B 1 +with a 10‐fold dynamic range (0.2–2 times the nominal B 1 + ). Moreover, the predominant use of low flip angle excitations in the presented sequence minimizes specific absorption rate, which is an important asset for in vivo B 1 + ‐shimming procedures at high magnetic fields. The proposed methodology was validated in phantom experiments and demonstrated good results in phantom and human B 1 + ‐shimming using an 8‐channel transmit‐receive array. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.