Dear Paul,

LTA means transformation matrix stored in .lta format.

This matrix can encode transformation between various coordinate spaces. 

What coordinate systems transform this .lta from and to is specified by string 
in the .lta file. Typically this type could be vox2RAS, RAS2vox, vox2vox or 
RAS2RAS. Most typically the type is vox2vox.

The explanation of coordinate systems is specified for example here:
http://freesurfer.net/fswiki/CoordinateSystems
http://www.grahamwideman.com/gw/brain/fs/coords/fscoords.htm

The output of freeview is only info, not error, indicating that your .lta is 
not of type vox2vox. I personally still use tkregister2 for checking of 
registration, since the freeview does not contain full functionality for 
checking transformations (see the warning).  Therefore I have no experience 
with tkregisterfv and consider tkregister2 still as a "gold standard". However, 
if you use tkregisterfv for checkning transformation between volumes and the 
output is only "info", I would guess that everything is OK and you do not need 
to be bothered. 

Btw, does the alignment of the images seem reasonable? How does it look in 
tkregister2?

Regards,

Antonin



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