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Orthogonalizing crusher and diffusion‐encoding gradients to suppress undesired echo pathways in the twice‐refocused spin echo diffusion sequence
Author(s) -
Nagy Zoltán,
Thomas David L.,
Weiskopf Nikolaus
Publication year - 2014
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.24676
Subject(s) - crusher , diffusion , spin echo , diffusion mri , signal (programming language) , imaging phantom , encoding (memory) , image quality , orientation (vector space) , nuclear magnetic resonance , computer science , physics , acoustics , materials science , optics , mathematics , geometry , image (mathematics) , artificial intelligence , magnetic resonance imaging , medicine , radiology , metallurgy , thermodynamics , programming language
Purpose The twice‐refocused spin echo sequence is widely used in diffusion imaging due to its excellent performance in reducing eddy currents. The three radio frequency pulses give rise to eight separate signal pathways. Because there is no general solution for the size and arrangement for crusher gradients, with constant size and orientation, that is effective for all arbitrary diffusion‐sensitizing b ‐values and directions, this article introduces and validates a solution whereby the crusher and diffusion‐encoding gradients are always kept orthogonal, thus ensuring their independence. Methods The cancellation of the crusher and diffusion gradients was demonstrated. Subsequently, crusher gradients were implemented in such a way that they were always orthogonal to the diffusion gradient. Phantom and in‐vivo experiments were performed to ascertain that orthogonally implemented crusher gradients alleviate the problem without lowering image quality. Results In all experiments, when the crusher gradients' action was cancelled by the diffusion‐encoding gradients artifactual signal modulation was observed. When orthogonal gradients were implemented the artifacts were eliminated without detrimental effects on image quality. Conclusions Orthogonal crushers are easy to implement and can be used for any variant of diffusion imaging sequences (e.g., diffusion tensor imaging, fiber diameter mapping) where the twice‐refocused scheme is used. Magn Reson Med 71:506–515, 2014. © 2013 Wiley Periodicals, Inc.