[Mne_analysis] MEG-MRI coordinate system alignment

[Hari Bharadwaj]

Hi,
   It uses whatever "subject-head.fif" surface lives in the Freesurfer
$SUBJECTS_DIR/$SUBJECT/bem/ directory. This is usually prepared by
mne_watershed_bem unless you created this using mne_surf2bem from
something else.

Also, the answer to your latter question depends on why you replaced the
surfaces from mne_watershed_bem...Assuming your previous registrations
were with a reasonable head surface, since the number of parameters for
the MEG head to MRI head transformation is small compared to the number of
digitizer points, I'd say it is not necessary to re-register.

HTH,
Regards,
Hari

On Sun, June 2, 2013 7:31 pm, Vincent Rupp Jr. wrote:
> Hi,
>
> According to the
> manual<http://martinos.org/mne/manual/analyze.html#coordinate-frame-alignment>,
> the MRI-MEG coordinate frame alignment tools included in mne_analyze
> utilize the 3D digitizer (Polhemus) data acquired in the beginning of each
> MEG/EEG session and the scalp surface triangulation. Specifically what
> scalp surface triangulation is used here? Is this something generated
> during FreeSurfer's recon-all stream, or is it the BEM mesh created with
> mne_watershed_bem?
>
> Ultimately, I am trying to understand how to solve this question: I
> recently overwrote my output from mne_setup_source_space,
> mne_watershed_bem, and mne_setup_forward_model. Do I need to re-register
> my
> MEG/MRI data before proceeding to compute the forward solution?
>
>
> Best wishes,
>
> Vincent Rupp Jr
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-- 
Hari Bharadwaj
PhD Candidate, Biomedical Engineering,
Boston University
677 Beacon St.,
Boston, MA 02215

Martinos Center for Biomedical Imaging,
Massachusetts General Hospital
149 Thirteenth Street,
Charlestown, MA 02129

hari at nmr.mgh.harvard.edu
Ph: 734-883-5954