[Freesurfer] extract beta values ROI

Hello,

I'm trying to extract beta values in cortical thickness analysis. For example, if I use qdec to look at the association between cortical thickness and variables A and B, can I extract the vertex-wise parameter estimates corresponding to the association between A and cortical thickness across subjects for a certain ROI? This ROI could be one of the regions from freesurfer parcellation or another saved ROI.

I can visualize the beta values by looking at beta.mgh in tksurfer but I'd like to be able to extract them in 'table' format. I think I know how to do extract summary statistics for an ROI, but I'd like instead to extract the betas for each vertex.

Many thanks for your help!

Lucia