Premium
Insight into in vivo magnetization exchange in human white matter regions
Author(s) -
Kalantari Saeed,
Laule Cornelia,
Bjarnason Thorarin A.,
Vavasour Irene M.,
MacKay Alex L.
Publication year - 2011
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.22873
Subject(s) - myelin , white matter , magnetization transfer , relaxation (psychology) , chemistry , magnetization , nuclear magnetic resonance , relaxometry , magnetic resonance imaging , biophysics , chemical physics , physics , central nervous system , magnetic field , neuroscience , biology , spin echo , medicine , quantum mechanics , radiology
Water exchange can play an important role in interpreting compartment‐specific magnetic resonance imaging data in brain. For example, an MR method of myelin measurement, known as myelin water fraction imaging, assumes that water exchange processes are slow compared with the measurement time scale. In this article, we examined whether water exchange processes have an effect on myelin water fraction values. A previously established four pool model of white matter was used to simulate the interactions between two aqueous compartments (myelin water and intra/extracellular water) and nonaqueous compartments (myelin and nonmyelin tissues). To extract the water exchange cross relaxation times, the Bloch equations were solved analytically. As the water exchange time scales are dependent on the spin‐lattice T 1 relaxation of each of these four pools and due to the current uncertainties regarding the T 1 associated with each pool, exchange cross relaxation times for three different T 1 scenarios were calculated. The corrections that need to be considered in order for myelin water fraction to be an accurate marker for myelin were found to be less than 15%. This work indicates that regional variations in white matter myelin water fraction values are most likely due to variations in myelin content rather than regional differences in exchange rates. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.