3dFWHMx on a single volume and on PET

Dear AFNI experts,

I have two related questions:

(1) Does 3dFWHMx work on a single volume?

(2) Does 3dFWHMx work well on PET images?

Based on my reading of the help menu, I am using this command to estimate the smoothness on amyloid PET images:

3dFWHMx -2difMAD -mask brain_mask+tlrc subject_718b_suvr+tlrc

Thank you.