Dear Alfonso,

I wonder what is the rationale behind choosing either the fixed erosion kernel (erosion steps) or fixed proportion of voxels post-erosion for the WM and the CSF masks for aCompCor. 

Is there an optimal range for the ratio of volumes before and after the erosion? I.e., QC_eroded_vol / QC_CSF_vol?

Thank you for your help.

Ekaterina