Hi-

Yes, to project data from a volume onto a surface, you can use 3dVol2Surf.

How did you create your surface? Did you use FreeSurfer's recon-all and then convert all the output to NIFTI+GIFTI dsets (where standard meshes are created, which are quite useful) with AFNI's @SUMA_Make_Spec_FS?

If you did use those couple of commands, then an example if your ROI is in the right hemisphere (rh) might be:

3dVol2Surf                          \
    -spec std.141.${subj}_rh.spec   \
    -surf_A  std.141.rh.smoothwm.gii \
    -map_func mask                   \
    -sv          DSET_ROI \
    -grid_parent DSET_ROI \
    -out_niml     std.141.rh.ROI_NAME.niml.dset

To view in suma, open your surfaces in SUMA:

suma -onestate -spec std.141.${subj}_both.spec -sv ${subj}_SurfVol.nii

.. then open the Surface Controller, select "Load Dset", (might have to change the list of dsets shown to have *rh* in it), and then view your dset. Is that reasonable?

NB: This video shows some of the visualization options for loading+viewing a dset:
[www.youtube.com]
(as well as drawing one, and other things with the SUMA GUI).

A lot of optionality with the mapping process dependes on:
+ does your ROI intersect clearly with the surface, or just bound on it?
+ are you aiming to project the ROI from being between two surfaces (like the GM-WM border and the pial), or just using one?

But the above is a starting point for mapping an ROI.

--pt