T2*-based fiber orientation mapping.

ABSTRACT: Recent MRI studies at high field have observed that, in certain white matter fiber bundles, the signal in T(2)*-weighted MRI (i.e. MRI sensitized to apparent transverse relaxivity) is dependent on fiber orientation ? relative to B(0). In this study, the characteristics of this dependency are quantitatively investigated at 7 T using ex-vivo brain specimens, which allowed a large range of rotation angles to be measured. The data confirm the previously suggested variation of R(2)* (=1/T(2)*) with ? and also indicate that this dependency takes the shape of a combination of sin2? and sin4? functions, with modulation amplitudes (=?R(2)*) reaching 6.44±0.15 Hz (or ?T(2)*=2.91±0.33 ms) in the major fiber bundles of the corpus callosum. This particular dependency can be explained by a model of local, sub-voxel scale magnetic field changes resulting from magnetic susceptibility sources that are anisotropic. As an illustration of a potential use of the orientation dependence of R(2)*, the feasibility of generating fiber orientation maps from R(2)* data is investigated.

SUBMITTER: Lee J 

PROVIDER: S-EPMC3119254 | biostudies-literature | 2011 Jul

REPOSITORIES: biostudies-literature