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Probing the myelin water compartment with a saturation‐recovery, multi‐echo gradient‐recalled echo sequence
Author(s) -
Kleban Elena,
Gowland Penny,
Bowtell Richard
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.28695
Subject(s) - white matter , corpus callosum , saturation (graph theory) , nuclear magnetic resonance , myelin , splenium , magnetization transfer , signal (programming language) , chemistry , amplitude , pulse sequence , physics , neuroscience , magnetic resonance imaging , biology , optics , mathematics , central nervous system , computer science , medicine , radiology , combinatorics , programming language
Purpose To investigate the effect of varying levels of T 1 ‐weighting on the evolution of the complex signal from white matter in a multi‐echo gradient‐recalled echo (mGRE) saturation‐recovery sequence. Theory and Methods Analysis of the complex signal evolution in an mGRE sequence allows the contributions from short‐ and long‐ T 2 ∗ components to be separated, thus providing a measure of the relative strength of signals from the myelin water, and the external and intra‐axonal compartments. Here we evaluated the effect of different levels of T 1 ‐weighting on these signals, expecting that the previously reported, short T 1 of the myelin water would lead to a relative enhancement of the myelin water signal in the presence of signal saturation. Complex, saturation‐recovery mGRE data from the splenium of the corpus callosum from 5 healthy volunteers were preprocessed using a frequency difference mapping (FDM) approach and analyzed using the 3‐pool model of complex signal evolution in white matter. Results An increase in the apparent T 1 as a function of echo time was demonstrated, but this increase was an order of magnitude smaller than that expected from previously reported myelin water T 1 ‐values. This suggests the presence of magnetization transfer and exchange effects which counteract the T 1 ‐weighting. Conclusion Variation of the B 1 + amplitude in a saturation‐recovery mGRE sequence can be used to modulate the relative strength of signals from the different compartments in white matter, but the modulation is less than predicted from previously reported T 1 ‐values.