Hi Gabriel,
They both represent anisotropy, but through different models. The dtifit FA map comes from the DTI model, the mean_f1samples from the ball & stick model.
The former models the signal through a single ellipsoidal compartment and FA reflects the anisotropy of this ellipsoid.
The latter is a multi-compartment model that describes diffusion as originating from different "pools", i.e. a ball compartment to capture perfectly isotropic diffusion and one or more stick compartments to capture diffusion perfectly diffusion along a fibre orientation. The mean_f1samples gives in every voxel the fraction of the signal that can be explained by the first anisotropic stick. Mean_f2samples gives the fraction explained by the second stick, etc.
Cheers
Stam
On 19 Jun 2013, at 14:58, Gabriel Castellanos wrote:
> Dear experts,
>
> What is the difference between the fa maps from dtifit and the fa maps after bedpostx (mean_f1samples)? Can the later be used to measure ROIs or TBSS?
>
> Thank you for your time in advance,
>
> Gabriel
>
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