ROI Analyses in FreeSurfer

Note: This is a short post jotting down my thoughts on FreeSurfer ROI analysis. This will be developed into a longer post later; however, this is a topic I've been looking into for some time, and I want to keep track of my sources. 

Regions of interest (ROIs) are groups of voxels that parameter estimates (or other data) are extracted from. With volumetric data, you specify the x-, y-, and z-coordinates of the origin for your ROI, and then build a sphere around it. (Spheres aren't the only method, but they are common.) You can do this with, for example: AFNI's 3dUndump; SPM's Marsbar toolbox; FSL's fslmaths.

I haven't been able to find out how to do a similar procedure with FreeSurfer. FS is 2D, so the ROI would probably be a circle instead of a sphere. Once your ROI is defined, then you could extract thickness, volume, and other measurements from the ROI.

See this post by Doug Greve about using a vertex as the base for an ROI:

Ordering of Options in Commands

Alert reader Surya recently pointed out how using different masks in the command fslstats led to the same result, leading him to question whether there was an error when creating the masks. 

The actual cause of the error, however, was in how the command was constructed. Here was the initial syntax:

fslstats image.nii.gz -M -k mask.nii.gz

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