You can do it in two ways.
- First, you can just apply mri_segstats with the --annot option to get the mean NODDI values using the ?h.aparc.stats file, then compute the LI on the ROIs
- Second, you can compute the map of the LI values (just added this here https://surfer.nmr.mgh.harvard.edu/fswiki/Xhemi), then use mri_segstats on the map to get the ROI means

The second option may be slightly preferred because the LI value will be representative of the vertices in the ROI. Also in ?h.aparc.annot were not generated in a symmetric way, so they may have asymmetries in them.

On 6/16/2021 8:29 AM, Gugger, James J wrote:

External Email - Use Caution

Good morning,

I am working with NODDI data and have created surface overlays in FreeSurfer space with NODDI values. I am interested in calculating vertex-wise asymmetry indexes utilizing fsaverage_sym similar to Greve et al Journal of Cognitive Neuroscience 25:9, pp. 1477–1492. I would ultimately like to extract average AIs for an ROI analysis. My question is how do I extract the overlay stats from the surface overlay mgh file to obtain average AI in each ROI?

Thanks!

Jim Gugger

James Gugger, MD, PharmD

Instructor of Neurology

University of Pennsylvania
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