ICV as a covariate

AFNI Message Board
1

Hi experts,

In 2nd level analysis, in which I use images from fMRI studies (for example, connectivity maps) and static PET images, should I add the ICV as a covariate?

Thank you very much in advance.

Best regards,
Marina.

2

should I add the ICV as a covariate?

This is a scientific (instead of statistical/modeling) question: add ICV as a covariate if you believe ICV modulates the relationship between FMRI and PET.

3

Thank you very much for your reply.

I think I didn’t explain the question well. The real question is whether when doing a voxel-wise analysis (or PET or fMRI, not both in the same analysis) it is mandatory to introduce the ICV as a covariate of no interest in the statistical model (as in VBM studies , which is mandatory).

For example, if you want to compare the voxel-wise differences of ReHo between controls and Alzheimer’s patients, is it necessary / mandatory to introduce the ICV as a variable of no interest?

Thank you very much in advance and sorry for the inconvenience.
Best regards,
Marina.