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Myelin water imaging depends on white matter fiber orientation in the human brain
Author(s) -
Birkl Christoph,
Doucette Jonathan,
Fan Michael,
HernándezTorres Enedino,
Rauscher Alexander
Publication year - 2021
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.28543
Subject(s) - white matter , myelin , voxel , nuclear magnetic resonance , orientation (vector space) , fiber tract , chemistry , magnetic resonance imaging , physics , biology , neuroscience , medicine , mathematics , central nervous system , radiology , geometry
Purpose The multi‐exponential T 2 decay of the MRI signal from cerebral white matter can be separated into short T 2 components related to myelin water and long T 2 components related to intracellular and extracellular water. In this study, we investigated to what degree the apparent myelin water fraction (MWF) depends on the angle between white matter fibers and the main magnetic field. Methods Maps of the apparent MWF were acquired using multi‐echo Carr‐Purcell‐Meiboom‐Gill and gradient‐echo spin‐echo sequences. The Carr‐Purcell‐Meiboom‐Gill sequence was acquired with a TR of 1073 ms, 1500 ms, and 2000 ms. The fiber orientation was mapped with DTI. By angle‐wise pooling the voxels across the brain’s white matter, orientation‐dependent apparent MWF curves were generated. Results We found that the apparent MWF varied between 25% and 35% across different fiber orientations. Furthermore, the selection of the TR influences the apparent MWF. Conclusion White matter fiber orientation induces a strong systematic bias on the estimation of the apparent MWF. This finding has implications for future research and the interpretation of MWI results in previously published studies.