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Single‐scan z‐shim method for reducing susceptibility artifacts in gradient echo myelin water imaging
Author(s) -
Lee Doohee,
Lee Jingu,
Lee Jongho,
Nam Yoonho
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.27127
Subject(s) - shim (computing) , gradient echo , nuclear magnetic resonance , myelin , in vivo , spin echo , imaging phantom , computer science , acoustics , biomedical engineering , materials science , magnetic resonance imaging , physics , biological system , optics , radiology , biology , medicine , neuroscience , microbiology and biotechnology , erectile dysfunction , central nervous system
Purpose Myelin water imaging (MWI) reportedly corresponds closely to the myelin content in the brain. An MWI technique based on multi‐echo gradient echo (mGRE) has recently been proposed as an alternative to the conventional spin‐echo‐based MWI. However, the mGRE signal is vulnerable to macroscopic field inhomogeneity, which makes MWI unreliable. In the present study, a z‐shim‐based single‐scan correction method is proposed to overcome this limitation. Methods Z‐shim gradients in the slice‐selection direction were added to an mGRE sequence after an echo time of 12 ms. A 3‐pool model corresponding to the proposed sequence was suggested for fitting the acquired signal. The method was evaluated through a comparison with methods without a correction and with post‐processing only from non‐z‐shimmed data. To do this, numerical simulations and in vivo experiments were conducted. Results The simulation and in vivo experiment results indicated that post‐processing alone was not sufficient to offset the macroscopic field inhomogeneity, particularly in inferior regions of the brain. On the other hand, the proposed method compensated the field inhomogeneity in most brain areas. The estimated in vivo myelin water fraction values were in good agreement with literature values obtained by previously proposed field inhomogeneity correction method. Conclusion The proposed method showed reliable myelin water fraction in most regions of the brain in vivo, including those with severe field inhomogeneity.