Brian,
Your question gets at the heart of the differences between AFM
(average fiducial mapping) and MFM (multi-fiducial mapping), which is
discussed in my 2005 Neuroimage paper.
In essence, the MFM value at a given node is the average of the value
for the corresponding nodes in the 12 fiducial subjects, and the
positions of these nodes is inherently variable. So the overall peak
will typically be lower with MFM than AFM. (The exception would be
if the average fiducial surface happened to miss the overall maximum
in the volume, which is possible but seems not to occur often.) But
it's not any simple linear transform.
The main advantage of MFM is that it gives you a better estimate of
the location of the peak(s), and we recommend it if that is your main
objective. If you need to hang onto the values of individual voxels,
then AFM is better.
If you're in a position to do surface-based analysis of individual
subjects, then spatial resolution improves substantially.
Hope this helps.
David
On Oct 9, 2007, at 6:54 PM, [EMAIL PROTECTED] wrote:
Caret folks-- I'm just starting to get acquainted with Caret and am
enjoying the
program.
I've been mapping my zstat_thresh file from FSL onto: 1) the PALS
brain, 2) the
AVG fiducial map, and 3) the multifiducial maps. The images I get
from 1 & 2
are
identical with the same Zmax (3.6) but #3 has a Zmax that is much
lower (2.8).
Is this supposed to happen? By playing with the Zmin on the
display, it looks
like there's some linear transformation going on for #2 vs. #3.
thanks for any suggestions,
Brian
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