> it was mentioned several times on the list that when doing the optimized
> VBM-procedure, no brainmask should be used. While I understand that it
> may not be advantagous since we are only dealing with brain-tissue
> anyhow, I wondered if there are instances where it may actually be
> harmful. Background is, if I want to compare data processed both ways, I
> would like to keep as much of the steps identical. Also, I may want to
> put at least some spatial restrictions on low-regularization
> normalization.
The "brain masking" is for weighting the spatial normalisation so that non-brain tissue
has less influence on the final result. It also reduces the influence in the registration
of voxels near the surface of the brain. Therefore, for images without extra-brain signal
(matched to a template without any non-brain signal), it is preferable to disable the
"brain masking", as it reduces the accuracy with which the brain surface is registered.
Best regards,
-John
--
Dr John Ashburner.
Functional Imaging Lab., 12 Queen Square, London WC1N 3BG, UK.
tel: +44 (0)20 78337491 or +44 (0)20 78373611 x4381
fax: +44 (0)20 78131420 http://www.fil.ion.ucl.ac.uk/~john
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