a) Since the procedure is the same as surface based analysis for cortical thickness except mri_vol2surf, Can I use the procedure for thickness? 

b) What is the difference between mris_preproc and mri_concat. If I use mris_preproc, do I also need to use mri_concat? Also, can I use mris_preproc instead of mri_concat? 

c) Can I use mri_surf2surf in place of mris_fwhm? If no, why? 

d) While researching PETsurfer surface based analysis in the forum, I came across multiple trends that used the "--projfrac" flag in both mri_vol2surf command and mris_preproc command. At what stage should I include this flag and why? 

e) If I want to perform a multimodal analysis using thickness&PET or Surface area&PET, Can anyone confirm if this is the correct steps. 

• Perform surface base analysis for cortical thickness from step 1 (mris_preproc) to correction for multiple comparison
• Perform PET surface based analysis from step 1 (gtmseg) to step 5. While conducting mri_glmfit, include the smoothed thickness map (?h.thickness.10B.mgh) as pvr (per vertex regressor) 
• e.g. mri_glmfit --y lh.pet.10.mgh --fsgd your.fsgd dods --pvr lh.thickness.10B.mgh --C contrast.mtx --surf fsaverage lh --cortex --glmdir pvr.lh.pet.thickness.glmdir
• Lastly, build a new monte carlo correction for multiple comparison. 

Thank you

Best, 

Paul