Hello,
I was wondering if someone could help us with a couple questions
regarding the stats/smoothness file.
According to this Mar 31, 2008 post in the archives from Tom (Re:
minimal smoothness and GRF Theory)
https://www.jiscmail.ac.uk/cgi-bin/webadmin?
A2=ind0803&L=FSL&P=R74667&1=FSL&9=A&I=-3&J=on&d=No+Match%3BMatch%
3BMatches&z=4
the relationship between RESELS and DHL is:
RESELS = (4*log(2))^(3/2) / DHL
But when I use that formula with the DLH in the smoothness file from a
Level 2 combination of runs, the calculated RESEL value doesn't match.
i.e.,
stats/smoothness file:
DLH 0.0609609
VOLUME 289699
RESELS 83.3048
whereas (4*log(2))^(1.5) / .0609609 = 75.7315
Is that formula no longer strictly true for higher level analyses?
Also, what would be the best way to convert a RESELS value to an AvgFWHM
in mm? Tom indicated that AvgFWHM = RESELS^(1/3), but that is in
voxels, and voxels at the first level are frequently not isotropic. So,
is the correct way to convert to AvgFWHM(mm) just:
AvgFWHM(mm) = (RESELS*pixdim1*pixdim2*pixdim3)^(1/3) ??
thanks,
-MH
--
Michael Harms, Ph.D.
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