Influence of white matter fiber orientation on R2* revealed by MRI segmentation.

PURPOSE

To investigate white matter heterogeneity using a multichannel segmentation of a large sample of structural and diffusion magnetic resonance imaging (MRI) data.

MATERIALS AND METHODS

A sample of 50 subjects was segmented using channels comprising exclusively structural (longitudinal and transverse relaxation times T1 and T2 and transverse relaxation rate R2*) and diffusion-based MRI indices (mean diffusivity and fractional anisotropy). These data were analyzed using a data driven approach in which no prior information was used.

RESULTS

The analysis revealed the splitting of white matter into two subclasses in which the longitudinal fasciculi were distinguished from inferior/superior ones. The distribution of the adopted indices in the obtained clusters showed that R2* was mainly responsible for this splitting.

CONCLUSION

This result supports the observation, previously hypothesized in the literature, that R2* is influenced by the fiber orientation.