Thanks for the reply, Karl. That was very helpful.
I re-looked at our data to check on the question of volume and it
raised new questions to my mind. I think, perhaps, I'm missing
something rather basic...
The volumes in our PET and fMRI data are different but they seem to
vary with the smoothing I applied. For instance, I smoothed both data
sets at 8, 12, and 16mm. The search volumes (in voxels) are displayed
below:
PET fMRI
8mm 187833 208800
12mm 213866 213245
16mm 237025 217173
(all voxels were isotropic 2mm^3). To me it seems like the
differences in volume were small which would make pretty good sense --
in both our PET and fMRI scanners we tried to acquire whole brain
images with approx ~15cm FOV.
What's odd, though, is that the calculated FWHM smoothness of our data
(in mm) are:
PET fMRI
8mm 8.0 9.4 10.8 15.8 14.9 10.7
12mm 11.0 13.0 14.7 22.7 20.9 13.8
16mm 14.5 17.1 19.1 23.5 21.9 15.5
Am I correct in reading these values as indicating that the fMRI data
was smoother than the PET data?
- Joe
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