Hi Dylan
Sorry, did anyone ever answer this? The .lta files contain the transform but
also information on the coordinate systems that they are in. I think that the
standard talairach one is voxel to voxel, so it would indeed change with the
image fov. There are tools for converting ltas to ras-to-ras, which I think is
what you want (although you will need to make sure you get the correct ras
space), but perhaps someone else can comment on this since I don't remember the
details?
Cheers
Bruce
-----Original Message-----
From: freesurfer-boun...@nmr.mgh.harvard.edu
<freesurfer-boun...@nmr.mgh.harvard.edu> On Behalf Of Tisdall, Dylan
Sent: Thursday, December 24, 2020 11:41 AM
To: freesurfer@nmr.mgh.harvard.edu
Subject: [Freesurfer] talairach.lta coordinate spaces
External Email - Use Caution
Hi list,
I'm trying to understand whether the talairach.lta transform is from the
image-axes RAS to talairach or the scanner-axes RAS to talairach. Basically, if
I rotate the imaging FOV and scan the same subject, should I expect that to
change talairach.lta or not? My confusion stems from the discrepancy between
what the scanner terms RAS coordinates (aligned to the gradient axes) vs. what
might be plausibly called RAS in the image coordinates (aligned to the FOV
axes).
The underlying goal here is to try to evaluate how gradient-axis-aligned
someone's head was when they were loaded in the scanner.
Thanks,
Dylan
---
Dylan Tisdall, PhD
Research Assistant Professor
Department of Radiology
Perelman School of Medicine
University of Pennsylvania
Room D406 Richards Medical Labs
3700 Hamilton Walk
Philadelphia, PA 19104
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