Dear Rick and Daniel,
Thank you very much. The 3dfractionize works well for this purpose. And this is an example of the good use of transforming from a low res to high res image, because of the -warp option.
Thanks for informing me of the DTIStudio functions. I did not know much about the DTI functions of AFNI, so I calculated eigenvector and FA in a third program from the DTI raw data, then tacked fiber in DTIStudio. So I will not take advantage of 3dAFNItoRaw or @DTI_studio_reposition. However, the DTIStudioFibertoSegments will be a great tool to visual lize the fiber in a 3D surface model.
Best,
Feng