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Design of spectral‐spatial phase prewinding pulses and their use in small‐tip fast recovery steady‐state imaging
Author(s) -
Williams Sydney N.,
Nielsen JonFredrik,
Fessler Jeffrey A.,
Noll Douglas C.
Publication year - 2018
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.26794
Subject(s) - bandwidth (computing) , imaging phantom , excitation , optics , spectral resolution , resonance (particle physics) , pulse (music) , pulse sequence , image resolution , physics , magnetic resonance imaging , nuclear magnetic resonance , spectral line , computer science , atomic physics , telecommunications , detector , medicine , quantum mechanics , astronomy , radiology
Purpose Spectrally selective “prewinding” radiofrequency pulses can counteract B0 inhomogeneity in steady‐state sequences, but can only prephase a limited range of off‐resonance. We propose spectral‐spatial small‐tip angle prewinding pulses that increase the off‐resonance bandwidth that can be successfully prephased by incorporating spatially tailored excitation patterns. Theory and Methods We present a feasibility study to compare spectral and spectral‐spatial prewinding pulses. These pulses add a prephasing term to the target magnetization pattern that aims to recover an assigned off‐resonance bandwidth at the echo time. For spectral‐spatial pulses, the design bandwidth is centered at the off‐resonance frequency for each spatial location in a field map. We use these pulses in the small‐tip fast recovery steady‐state sequence, which is similar to balanced steady‐state free precession. We investigate improvement of spectral‐spatial pulses over spectral pulses using simulations and small‐tip fast recovery scans of a gel phantom and human brain. Results In simulation, spectral‐spatial pulses yielded lower normalized root mean squared excitation error than spectral pulses. For both experiments, the spectral‐spatial pulse images are also qualitatively better (more uniform, less signal loss) than the spectral pulse images. Conclusion Spectral‐spatial prewinding pulses can prephase over a larger range of off‐resonance than their purely spectral counterparts. Magn Reson Med 79:1377–1386, 2018. © 2017 International Society for Magnetic Resonance in Medicine.