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Efficient bloch‐siegert B 1 + mapping using spiral and echo‐planar readouts
Author(s) -
Saranathan Manojkumar,
Khalighi Mohammad Mehdi,
Glover Gary H.,
Pandit Prachi,
Rutt Brian K.
Publication year - 2013
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.24599
Subject(s) - physics , spiral (railway) , echo planar imaging , pulse (music) , nuclear magnetic resonance , planar , offset (computer science) , sensitivity (control systems) , echo (communications protocol) , optics , materials science , magnetic resonance imaging , computer science , mathematics , medicine , radiology , mathematical analysis , computer network , computer graphics (images) , electronic engineering , detector , programming language , engineering
The Bloch‐Siegert (B‐S) B 1 + mapping technique is a fast, phase‐based method that is highly SAR limited especially at 7T, necessitating the use of long repetition times. Spiral and echo‐planar readouts were incorporated in a gradient‐echo based B‐S sequence to reduce specific absoprtion rate (SAR) and improve its scan efficiency. A novel, numerically optimized 4 ms B‐S off‐resonant pulse at + 1960 Hz was used to increase sensitivity and further reduce SAR compared with the conventional 6 ms Fermi B‐S pulse. Using echo‐planar and spiral readouts, scan time reductions of 8–16 were achieved. By reducing the B‐S pulse width by a factor of 1.5, SAR was reduced by a factor of 1.5 and overall sensitivity was increased by a factor of 1.33 due to the nearly halved resonance offset of the new B‐S pulse. This was validated on phantoms and volunteers at 7 T. Magn Reson Med 70:1669–1673, 2013. © 2013 Wiley Periodicals, Inc.