I am trying to draw my own ROIs and would like to measure the volume contained within them. I was trying to get afni to extrapolate ROIs in intermediate sections if I only use every third section to hand draw the ROI and am having a hard time understanding the documentation I found.
I am trying to measure the volume of the lateral, third and fourth ventricle as well as the whole brain volume for comparison. I do not want to measure the activity of voxels within, just the mm3 or ml contained within my areas of interest. I was trying to find a function in afni that would allow me to autmatically register negative space (the ventricles) with a value of zero to automate this function. I've read that SIENA in FSL is able to measure whole brain volume and the volumes of specific brain regions as well as ventricles. So I was wondering if afni can do the same thing.

Thank you very much

Sabrina