Hi Miguel
Our supported way of doing tractography using a protocol defined in MNI space (and saving tractography results in MNI space as well) is providing the warp fields to probtrackx, which internally will bring the protocol to diffusion space, perform tractography in diffusion space and then transform the results back to MNI space.
In theory you could do what you suggest, even if consistencies like Sumf_i=1 are not guaranteed when you apply the warps, so you need to be careful with the interpolation you use. As vecreg expects vectors defined in cartesian coordinates as input, while bedpostx outputs vector samples in spherical coordinates, you need to take every bpx sample from spherical to cartesian form, then apply vecreg, then transform back to spherical coordinates and recreate the merged_samples files.
Hope this helps
Stam
> On 14 Jan 2019, at 20:45, Miguel Sotelo <[log in to unmask]> wrote:
>
> Hello FSL community
>
> My question is more of a theoretical one.
> Given that I have my bedpostX (3D and 4D) image files in the subject's native diffusion space, and affine and warp fields that map from the subject's native diffusion space to a template space (say, MNI): Would I be able to apply these warp fields to my bedpostX images to yield bedpostX images (3 and 4D) in my template space?
>
> I ask this in order to avoid performing tractography in the native diffusion space (my warp fields were created using ANTs).
>
> A similar question was asked in October 2008 (vecreg for merged_ph, etc), but I do not understand the proposed solution of transforming each sample into vector form.
>
> THANK YOU
>
> -
> Miguel
>
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