I am trying to get a gray matter mask for my group using a mean image of all
subjects' mprages. I am getting a large ring around my gray matter mask,
where there is a mm or so of gray matter than isn't captured into the mask.
This is despite the fact that the tpm for the gray matter goes all the way
to the edges of my group mprage. Does anyone know a way to reduce or
completely remove this ring and ensure that all of the gray matter, to the
very edge of the brain is included in the gray matter mask? Thank you.