In order to perform group statistics,
the fMRI data should be normalized to a standard size.
The
standard size (talairach) is 13.5 x 17.5 x 12.0 cm.
The normalization amounts to a linear scaling in
the x,y, and z-direction.
The parameter '-system' specifies the coordinate system.
If the system is 'talairach' then the brain extent in x,y,z is
set to (120 mm,175 mm,135 mm).
If '-system' is set to 'mni' then the extent is
(128 mm,177 mm,141 mm).
The program that performs the normalization is called 'vnormalize'.
The normalization can be applied to the transformation matrix obtained
from 'vreg3d'. In this case, the transformation matrix is multiplied
by linear scaling factors. If the normalized transformation matrix
is then applied using either
'vdotrans' or
'vfunctrans', the resulting
3D images will not only be registered to the 3D reference data set,
but also linearly scaled to a standard size.
To do this, use the following processing chain:
vreg3d -> vnormalize -> vdotrans/vfunctrans.
Example:
vnormalize -in AC1T_trans.v -out AC1T_ntrans.v
The normalization can also be applied to a 3D image such as a registered zmap
or an anatomical 3D image of the image data base. Note that the reference images
in the image data base '/home/newbdb/' are not normalized.
Example:
vnormalize -in infile.v -out outfile.v