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Parallel‐transmission‐enabled three‐dimensional T 2 ‐weighted imaging of the human brain at 7 Tesla
Author(s) -
Massire Aurélien,
Vignaud Alexandre,
Robert Benjamin,
Le Bihan Denis,
Boulant Nicolas,
Amadon Alexis
Publication year - 2015
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.25353
Subject(s) - image quality , computer science , parallel communication , pulse sequence , excitation , flip angle , physics , nuclear magnetic resonance , homogeneity (statistics) , transmission (telecommunications) , white matter , optics , segmentation , magnetic resonance imaging , artificial intelligence , image (mathematics) , telecommunications , medicine , quantum mechanics , machine learning , radiology
Purpose: A promise of ultra high field MRI is to produce images of the human brain with higher spatial resolution due to an increased signal to noise ratio. Yet, the shorter radiofrequency wavelength induces an inhomogeneous distribution of the transmit magnetic field and thus challenges the applicability of MRI sequences which rely on the spin excitation homogeneity. In this work, the ability of parallel‐transmission to obtain high‐quality T 2 ‐weighted images of the human brain at 7 Tesla, using an original pulse design method is evaluated. Methods: Excitation and refocusing square pulses of a SPACE sequence were replaced with short nonselective transmit‐SENSE pulses individually tailored with the gradient ascent pulse engineering algorithm, adopting a k T ‐point trajectory to simultaneously mitigate B 1 + and ΔB 0 nonuniformities. Results: In vivo experiments showed that exploiting parallel‐transmission at 7T with the proposed methodology produces high quality T 2 ‐weighted whole brain images with uniform signal and contrast. Subsequent white and gray matter segmentation confirmed the expected improvements in image quality. Conclusion: This work demonstrates that the adopted formalism based on optimal control, combined with the k T ‐point method, successfully enables three‐dimensional T 2 ‐weighted brain imaging at 7T devoid of artifacts resulting from B 1 + inhomogeneity. Magn Reson Med 73:2195–2203, 2015. © 2014 Wiley Periodicals, Inc.