Composite RF pulses for B1+-insensitive volume excitation at 7 Tesla.

Moore J, Jankiewicz M, Zeng H, Anderson AW, Gore JC
J Magn Reson. 2010 205 (1): 50-62

PMID: 20451430 · PMCID: PMC2885526 · DOI:10.1016/j.jmr.2010.04.002

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.

Copyright (c) 2010 Elsevier Inc. All rights reserved.

MeSH Terms (10)

Algorithms Brain Computer Simulation Electromagnetic Fields Humans Image Processing, Computer-Assisted Magnetic Resonance Imaging Phantoms, Imaging Radio Waves Software

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