afni.nimh.nih.gov

Dear experts
Hi
I would like to render my structural brain image which is registered to MNI (i.e "st+orig.HEAD,st+orig.BREAK" in "/root/Desktop " ) and get a 3D image.
As far as I know I should proceed as "Define Datamode ---> Plugins ---> Render [new]" .
However,I could not load my image in "choose underlay dataset".
What should I do as the next step?
Many thanks in advance.

Best,
Mahsa