>I think you are right Stephen, moreover the same considerations must
>apply to signal loss due to B0 inhomogenities.
>So once again what is the rationale behind GMI scaling in fMRI.
aha - GMI still makes a lot of sense, independent of the
%change question. GMI means that cross-subject comparisons
are valid. For example, random effects analyses simply
take in the first-level parameter estimates, so these should
all have been estimated from data which was (roughly at least)
of the same intensity levels.
thanks, Steve.
Stephen M. Smith
Head of Image Analysis, FMRIB
Oxford University Centre for Functional MRI of the Brain
John Radcliffe Hospital, Headington, Oxford OX3 9DU, UK
+44 (0) 1865 222726 (fax 222717)
[log in to unmask] http://www.fmrib.ox.ac.uk/~steve
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