[Freesurfer] question about spmregister-sess

Hi,

I am trying to register my functional images with a high resolution anatomical image. I am getting a really bad registration.

The anatomical image has the following stats:

Dimension : 126x165x103 Voxel size : 1 x 1 x 1 Fov : 165 nFrames : 1 Orientation: RPI Primary Slice Direction : axial

The functional image has :

Dimension : 84 x 96 x 33 x158 Voxel size : 1.4583 x 1.4583 x 1.5 Fov : 84 nFrames : 158 Orientation: RPI Primary Slice Direction : axial

I am using the following command to do the registration:

"Spmregister-sess -sf sessid -df sesspar "

It looks like something to do with the scaling factor. But, I have no idea how to change it. Any help will be welcome..

-Krishna