Hello,
I have a question regarding nifti (.nii) input files. I have .nii image files, which are aligned to AC-PC with SPM. The actual (original) data in this file is not changed, but the transformation matrix is saved in the .nii file.
When displaying the freesurfer reconstructed results with tkmedit, the images are tilted (AC-PC aligned). So it seems that freesurfer reads and applies the transformation saved in the nii file.
Is that true? and if yes at which step?
When using the recon-all -i command to create the starting folders and mgz files before starting the actual freesurfer processing, is the transformation matrix used to realign the images during this first process, and the following processing is done on the reoriented image? or is it just used for display? Or is the fact that the image appears tilted a result of the Talairach transform and the nii header was not read at all?
I am asking because, I have subjects which were SPM aligned, and subject which were not. I am wondering if it makes any difference, since due to an initial reorientation data will be interpolated and maybe a bit smoothed, compared to data which was not aligned before.
Does anybody have any experience with that and a feeling if an reorientation beforehand would have an effect on the outcome for cortical thickness maesures?
Thaks for any comments, Chris