Dear FreeSurfer experts,

I would like to enquire about the command mri_extract_label. More specifically I am looking for information about the -erode argument. Therefore I have a few questions:

Is a 3D erosion of the entire brain or a 2D slice by slice erosion used?
What structuring element (regarding the shape and size of the kernel) is used for the erosion for a given argument value (e.g. for the command mri_extract_label -erode 1)?

Thank you in advance!