Hi Matt,
I am trying to perform what you have suggested, to apply the non-linear transform obtained from TBSS to transform an ROI defined in MNI space to a subject's native diffusion space for probtrackx. I would like to make sure if I am doing it right. Many thanks in advanced.
From the outputs of TBSS, for each subject we have the warp field (FA_to_target_warp.nii.gz) and the affine transform
(target_to_FA.mat)
then I did
invwarp --warp=FA_to_target_warp.nii.gz --out=target_to_FA_warp --ref=FMRIB58_FA_1mm.nii.gz
to get the non-linear transformed needed to put the ROI to the subjects' native diffusion space.
and here are my questions:
1) Do we need to care about the affine transform anymore? That is, when doing the applywarp, do we need to put it as --premat or --postmat?
2) I performed the applywarp twice to check if the transform works:
applywarp --ref=FMRIB58_FA_1mm.nii.gz --in=dti_FA.nii.gz --warp=FA_to_target_warp.nii.gz --out=warpped_FA
applywarp --ref=FMRIB58_FA_1mm.nii.gz --in=warpped_FA.nii.gz --warp=target_to_FA_warp.nii.gz --out=re-warpped_FA
while the warpped_FA matches the FMRIB58 very well, the re-warpped_FA does not match the subject's native FA image that a large portion of it was cropped. also, the dimension of the re-warpped_FA does not match the original dti_FA. Something must be wrong in the process.
3) Does probtrackx really accept the warp fileds as --xfm and --invxfm? Cos in fdt_gui, there is no such option to perform a non-linear transform.
Thanks,
Francis
|