[Mne_analysis] Source points omitted with mne_forward_solution

[Matti Hamalainen]

Hi Andres,

It is because of the --mindist 5 option. This means that any points  
closer than 5 mm to inner skull surface are omitted. The rationale  
behind this is (or used to be) that the BEM  forward solution gets  
inaccurate when the sources are close to the inner skull surface. With  
the now standard 5120-triangle surfaces it is most probably safe to  
omit the --mindist 5 option.

- Matti

On Feb 25, 2010, at 3:36 PM, Andres Felipe Salazar Gomez wrote:

> Hi MNE users,
>
> I am getting some source points omitted when running  
> mne_forward_model and
> I was wondering if anyone knows the possible reasons for this to be
> happening. I run the mne_watershead_bem to get the BEM model but  
> also used
> seglab to get a inner_skull.tri file.
>
> Somehow the sources are crossing the inner_skull boundary. Where do  
> you
> recommend me to focus in order to understand what really is causing  
> this
> problem?  In my further analysis I will need the sources neighbors so
> missing sources is a problem.
>
> - Here is the code:
>
> mne_forward_solution --src
> $SUBJECTS_DIR/$SUBJECT/bem/structural_mri-ico-5-src.fif --mri
> $SUBJECTS_DIR/$SUBJECT/mri/T1-neuromag/sets/COR- 
> asalazar-090406-142236.fif
> --meas $SUBJECTS_DIR/$SUBJECT/eeg_mri/base/dec_base_raw-ave.fif --bem
> $SUBJECTS_DIR/$SUBJECT/bem/structural_mri-5120-5120-5120-bem-sol.fif  
> --fwd
> dec_base_raw-ave-ico-5-fwd.fif --eeg --mindist 5 --fixed
>
> - I am getting this 30 sources omitted:
>
> Source spaces are in head coordinates.
> Checking that the sources are inside the inner skull and at least     
> 5.0
> mm away (will take a few...)
> 14 source space points omitted because they are outside the inner  
> skull
> surface.
> 715 source space points omitted because of the    5.0-mm distance  
> limit.
> 16 source space points omitted because they are outside the inner  
> skull
> surface.
> 788 source space points omitted because of the    5.0-mm distance  
> limit.
> Thank you for waiting.
>
> Thank you in advance for any tips or ideas,
>
> -- 
> Andres F. Salazar
> Research Technologist
> Neuroscience Statistics Research Laboratory
> asalazar at nmr.mgh.harvard.edu
> 149 13th Street, Room 4005
> Charlestown, MA  02129
>
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