Composite RF pulses for B1+-insensitive volume excitation at 7 Tesla.
A new class of composite RF pulses that perform well in the presence of specific ranges of B0 and B1+ inhomogeneities has been designed for volume (non-selective) excitation in MRI. The pulses consist of numerous (approximately 100) short (approximately 10 micros) block-shaped sub-pulses each with different phases and amplitudes derived from numerical optimization. Optimized pulses are designed to be effective over a specific range of frequency offsets and transmit field variations and are thus implementable regardless of field strength, transmit coil configuration, or the subject-specific spatial distribution of the static and RF fields. In the context of 7 T human brain imaging, both simulations and phantom experiments indicate that optimized pulses result in similar on-resonance flip-angle uniformity as BIR-4 pulses but with the advantages of superior off-resonance stability and significantly reduced average power. The pulse design techniques presented here are thus well-suited for practical application in ultra-high field human MRI.
Moore
Jay
J
Institute of Imaging Science, Vanderbilt University, 1161 21st Ave. South, MCN AA-1105, Nashville, TN 37232-2310, USA. jay.moore@vanderbilt.edu
Jankiewicz
Marcin
M
Zeng
Huairen
H
Anderson
Adam W
AW
Gore
John C
JC
D000465:Algorithms; D001921:Brain / Q000033:anatomy & histology; D003198:Computer Simulation; D004574:Electromagnetic Fields; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging / Q000379:methods*; D019047:Phantoms, Imaging; D011846:Radio Waves; D012984:Software
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