manually specifying fiducial positions in MRI structure

Markus Bauer m.bauer at UCL.AC.UK
Sat Apr 17 02:45:13 CEST 2010


I have been using the new *SPM mesh* (fitted to the individual MRI by
the inverse transformation matrix of MRI -> MNI) *for creating forward
models for source-analysis for CTF data in fieldtrip.*

That works quite well, however, when trying to plot the results in
fieldtrip I face the problem that the *sources and the MRI *(read into
fieldtrip using read_mri and the SPM8 toolbox) *have different
coordinate systems*.

How can I recompute the coordinates of the MRI so that it is in
fieldtrip (CTF-head-coordinates) format?
I have the fiducial info from SPM available...
Is it possible to do sth like:

pos = mri.transform * mri.ind;
pos = pos - fiducial.pos; %or whatever - do a translation to the origin
of the 'new coordinate system'
mri.transform = pos  / ind;

or is it also necessary to flip the dimensions / specify further info??
cause I think MRI's in SPM have the x- and y-axis flipped compared to
the CTF/fieldtrip headmodel format...

Any suggestions would be appreciated, thanks

The aim of this list is to facilitate the discussion between users of the FieldTrip  toolbox, to share experiences and to discuss new ideas for MEG and EEG analysis. See also and
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