CAT12 VBM - clusters of voxels outside the glass brain

Software Support
1

When I performed VBM using CAT12, I could see a cluster of voxels outside the glass brain. I segmented GM using CAT12 and then performed “Fexlible factorial” using SPM. It would be really helpful if anyone could let me know the potential reasons for this. Also, is it okay to have a cluster of voxels outside the glass?

2

Two reasons comes to mind:

  • Did you supply a binary mask of where the analysis should be conducted. Commonly, the probability grey matter (p1 prefix in CAT12) of healthy controls is averaged and thresholded to some commonly-used value like 20%.

Something like this, to constrain the analysis within:
image

  • The SPM glass brain outline is a tad eroded. You can cross-reference through other tools like nilearn or MRIcronGL.