Hi Antonella,

The eigvals.nii is a 4D file that consists of 3 frames. Each corresponding to the respective eigenvectors.

You can do the following to split them up:

fslsplit eigvals.nii eigval

This will give you three volumes:

eigval0000.nii.gz - Axial/Parallel Diffusivity

Mean of the volumes below gives you Radial/perpendicular diffusivity eigval0001.nii.gz eigval0002.nii.gz

mv eigval0000.nii.gz Axial_Diffusivity.nii.gz

To get the radial diffusivity you have to get the mean of the other two eigen values:

fslmaths eigenval0001.nii.gz -add eigval0002.nii.gz -div 2 Radial_Diffisivity.nii.gz

Priti

Dear All,

I was running dt_recon on my DTI data and one output file is the eigvals.nii -- maps of the eigenvalues. I know that the diffusivity along the principal axis, λ1 represents the longitudinal diffusivity or the axial diffusivity (or even the parallel diffusivity λ∥).Can you please advise me how I can get my first eigenvalueλ1 from my maps of the eigenvalues?Â

Thank you for your time and help. AK _______________________________________________ Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer