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Volumetric B 1 + Mapping of the Brain at 7T using DREAM
Author(s) -
Nehrke Kay,
Versluis Maarten J.,
Webb Andrew,
Börnert Peter
Publication year - 2014
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.24667
Subject(s) - specific absorption rate , relaxation (psychology) , isotropy , nuclear magnetic resonance , physics , materials science , computer science , optics , psychology , social psychology , telecommunications , antenna (radio)
Purpose To tailor and optimize the Dual Refocusing Echo Acquisition Mode (DREAM) approach for volumetric B 1 + mapping of the brain at 7T. Theory and Methods A new DREAM echo timing scheme based on the virtual stimulated echo was derived to minimize potential effects of transverse relaxation. Furthermore, the DREAM B 1 + mapping performance was investigated in simulations and experimentally in phantoms and volunteers for volumetric applications, studying and optimizing the accuracy of the sequence with respect to saturation effects, slice profile imperfections, and T 1 and T 2 relaxation. Volumetric brain protocols were compiled for different isotropic resolutions (5–2.5 mm) and SENSE factors, and were studied in vivo for different RF drive modes (circular/linear polarization) and the application of dielectric pads. Results Volumetric B 1 + maps with good SNR at 2.5 mm isotropic resolution were acquired in about 20 s or less. The specific absorption rate was well below the safety limits for all scans. Mild flow artefacts were observed in the large vessels. Moreover, a slight contrast in the ventricle was observed in the B 1 + maps, which could be attributed to T 1 and T 2 relaxation effects. Conclusion DREAM enables safe, very fast, and robust volumetric B 1 + mapping of the brain at ultrahigh fields. Magn Reson Med 71:246–256, 2014. © 2013 Wiley Periodicals, Inc.