I used mri_coreg to register my pet data to T1 like below:

          mri_coreg --mov pet.nii.gz --ref T1.nii --reg pet_T1.reg.lta

After coregistering, I checked the registration using tkregisterfv like below:

          tkregisterfv --mov pet.nii.gz --targ T1.nii --reg pet_T1.reg.lta

However, the command didn't work with an error: 

          if: Expression Syntax.

Any suggestions would be appreciated. Thank you in advance for your help.

Sincerely,

Vicky