[Freesurfer] extract values for significant cluster

Dear FreeSurfer experts,

in the longitudinal 2 stage model I find a difference in rate between my two groups in right intra parietal sulcus for surface area (survives MC correction). I would like to look at the cortical thickness in that same cluster. Is it possible to use any of the output files from the MC correction as a mask or something to get the rate of change values for thickness in that region? Even though this region does not show a significant difference between the groups I would like to look at the individual values for rate of change in that specific region (like the ones I received in the cache.th30.abs.y.ocn.dat file)

Could you please tell me if this is possible and how?

Thank you very much! Clara