An R2* model of white matter for fiber orientation and myelin concentration

Abstract

Myelin, which consists of lipid bilayers, is one of the major constituents of white matter in the brain and has been suggested as a primary source of magnetic susceptibility contrasts. In this study, a new R₂* model that simultaneously explains the effects of fiber orientation and myelin concentration is proposed and tested. In addition, a new approach that produces R₂* maps without the effects of myelin is suggested. Experimental results demonstrate that the model reveals a high goodness of fit for the R₂* distribution of white matter compared to a model that explains either fiber orientation or myelin concentration. The proposed R₂* map shows a relatively uniform spatial distribution of R₂* compared to the uncorrected R₂* map and the fiber orientation or myelin concentration corrected R₂* map.

Keywords: Fiber orientation; Gradient-echo myelin water imaging (GRE-MWI); Magnetic susceptibility; Myelin concentration; R(2)*.