Mechanisms of T2* anisotropy and gradient echo myelin water imaging

Jongho Lee, Yoonho Nam, Joon Yul Choi, Eung Yeop Kim, Se Hong Oh, Dong Hyun Kim

Research output: Contribution to journalReview articlepeer-review

32 Citations (Scopus)


In MRI, structurally aligned molecular or micro-organization (e.g. axonal fibers) can be a source of substantial signal variations that depend on the structural orientation and the applied magnetic field. This signal anisotropy gives us a unique opportunity to explore information that exists at a resolution several orders of magnitude smaller than that of typical MRI. In this review, one of the signal anisotropies, T2* anisotropy in white matter, and a related imaging method, gradient echo myelin water imaging (GRE-MWI), are explored. The T2* anisotropy has been attributed to isotropic and anisotropic magnetic susceptibility of myelin and compartmentalized microstructure of white matter fibers (i.e. axonal, myelin, and extracellular space). The susceptibility and microstructure create magnetic frequency shifts that change with the relative orientation of the fiber and the main magnetic field, generating the T2* anisotropy. The resulting multi-component magnitude decay and nonlinear phase evolution have been utilized for GRE-MWI, assisting in resolving the signal fraction of the multiple compartments in white matter. The GRE-MWI method has been further improved by signal compensation techniques including physiological noise compensation schemes. The T2* anisotropy and GRE-MWI provide microstructural information on a voxel (e.g. fiber orientation and tissue composition), and may serve as sensitive biomarkers for microstructural changes in the brain.

Original languageEnglish
Article numbere3513
JournalNMR in Biomedicine
Issue number4
Publication statusPublished - 2017 Apr 1

Bibliographical note

Funding Information:
The authors thank Dr Jeff H. Duyn for helpful discussion. This research was supported by the Brain Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT and Future Planning (NRF-2015M3C7A1031969) and by the Korean Government (MSIP) (NRF-2015R1A5A7037676) and (NRF-2015R1A2A1A15052174).

Publisher Copyright:
Copyright © 2016 John Wiley & Sons, Ltd.

All Science Journal Classification (ASJC) codes

  • Molecular Medicine
  • Radiology Nuclear Medicine and imaging
  • Spectroscopy


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