I used partsurfer in FS6 and had applied partial volume correction (PVC) on PET data. I followed the same steps as in wiki which was very well explained! Thank you!.

The analyses went fine... I would like to inquire about some issues, and I highly appreciate any clarification:

1. The flag --psf in "mri_gtmpvc": Is the value of "psf" means the amount of smoothing (fwhm in mm) that will be applied on the corrected maps? If I give "psf" a value of "zero", does this means that the corrected maps are no longer going to be smoothed? The motivation of the question is that I would like to smooth the images at the end of the analysis, so I can apply the amount of smoothing on the PVC images vs analysis involve non-pvc images.

2. For some of my group analyses, I don't see any difference between the groups. When I apply PVC using "mri_gtmpvc", I see difference in pathologically relevant regions, and vice versa for some other analyses where I see difference between the groups without PVC then the difference disappear following PVC. I highly appreciate if you please clarify why PVC can find results or eliminate findings. What is the idea of partial volume effect PVE in this case?

3. Group analysis: following PVC, I used "mri_concat" to combine the images "?.mgx.gm.nii.gz", then I smoothed the final combined images using the flag "fwhm" in "mri_surf2surf". I used fwhm=3mm and then fwhm=6mm. For all analyses I can see clusters of difference between the groups at fwhm=3mm. For some analyses the difference disappears when I use fwhm=6mm . Is this till a partial volume effect even after applying pvc or this is relevant to an extra smoothing effect which obscure the PET signal? is there any recommended fwhm value for PET images?