Hi, Peng Ren-

This is the orientation information:

3dinfo -orient FILE

... which in your file's case is RPI. The part of the header describing/showing this orientation information is:

first (x) = Right-to-Left
second (y) = Posterior-to-Anterior
third (z) = Inferior-to-Superior [-orient RPI]

You can change the orientation with something like

3dresample -orient AIL -prefix NEWFILE -inset FILE

and see that the above all changes to match.

The other information you point out:

 R-to-L extent: -102.774 [R] -to- 105.914 [L] -step- 3.312 mm [ 64 voxels]
A-to-P extent: -89.485 [A] -to- 119.203 [P] -step- 3.312 mm [ 64 voxels]
I-to-S extent: -44.866 -to- 110.822 [S] -step- 3.312 mm [ 48 voxels]

does *not* change with defining a new orientation with 3dresample. This is the dataset field of view information-- what is teh extent that 3D rectangle/box takes up in physical space (showing the "extent" values along with the voxel dimensions and matrix size). It is always just shown in the "AFNI standard" ordering with the RAI side of things listed first. The FOV/extents don't change just by resampling orientation.

Note that when you resample, the "origin" value changes-- it is basically the corner of the dataset defined by the orientation. That changes along with the orientation when you resample.

--pt