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Neuroimage. 2019 Oct 1;199:545-552. doi: 10.1016/j.neuroimage.2019.05.042. Epub 2019 May 17.

The influence of brain iron on myelin water imaging.

Author information

1
UBC MRI Research Centre, University of British Columbia, Vancouver, BC, Canada; Department of Neurology, Medical University of Graz, Austria. Electronic address: christoph.birkl@ubc.ca.
2
Department of Pathology, Neuropathology and Molecular Pathology, Medical University of Innsbruck, Austria; Diagnostic and Research Institute of Pathology, Medical University of Graz, Austria.
3
Institute of Neurology, Medical University of Vienna, Austria.
4
Department of Biomedical Imaging and Image-Guided Therapy, Medical University of Vienna, Austria.
5
Department of Cellular & Physiological Sciences, University of British Columbia, Vancouver, BC, Canada.
6
Department of Pathology, Neuropathology and Molecular Pathology, Medical University of Innsbruck, Austria; Diagnostic and Research Institute of Pathology, Medical University of Graz, Austria; Department of Pathology, Medical Faculty, Otto-von-Guerecke University Magdeburg, Germany.
7
UBC MRI Research Centre, University of British Columbia, Vancouver, BC, Canada; Department of Physics & Astronomy, University of British Columbia, Vancouver, BC, Canada; Department of Pediatrics (Division of Neurology), University of British Columbia, Vancouver, BC, Canada.

Abstract

With myelin playing a vital role in normal brain integrity and function and thus in various neurological disorders, myelin sensitive magnetic resonance imaging (MRI) techniques are of great importance. In particular, multi-exponential T2 relaxation was shown to be highly sensitive to myelin. The myelin water imaging (MWI) technique allows to separate the T2 decay into short components, specific to myelin water, and long components reflecting the intra- and extracellular water. The myelin water fraction (MWF) is the ratio of the short components to all components. In the brain's white matter (WM), myelin and iron are closely linked via the presence of iron in the myelin generating oligodendrocytes. Iron is known to decrease T2 relaxation times and may therefore mimic myelin. In this study, we investigated if variations in WM iron content can lead to apparent MWF changes. We performed MWI in post mortem human brain tissue prior and after chemical iron extraction. Histology for iron and myelin confirmed a decrease in iron content and no change in myelin content after iron extraction. In MRI, iron extraction lead to a decrease in MWF by 26%-28% in WM. Thus, a change in MWF does not necessarily reflect a change in myelin content. This observation has important implications for the interpretation of MWI findings in previously published studies and future research.

KEYWORDS:

Brain; Iron; Myelin; Myelin water imaging; Quantitative MRI; White matter

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