Contralateral scout projection error

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1

Hi,

I am trying to project some scouts from one subject to another, and then compute the cotralateral part in order to test some EEG ERSD data. It generally works fine, no problem so far in projecting from one subject to others. However, for some subjects, there seem to be some vertices that belong both to the left and right hemisphere.

I tried intersecting each scout with the scouts of left and tight hemisphere, and found no scouts with vertices in both of them. I then opened bst_project_scouts_contra and found the problem.

At row 64:

if isfield(sSurf, 'tess2tess_interp') && all(isfield(sSurf.tess2tess_interp, {'Signature_LR', 'Wmat_LR', 'Wmat_RL'})) && ...
            strcmpi(sSurf.tess2tess_interp.Signature_LR, Signature_LR) && \~isempty(sSurf.tess2tess_interp.Wmat_LR)

I found at sLORETA scouts mirror image of another - #3 by Raymundo.Cassani that matrices Wmat_LR and Wmat_RL are computed only if FreeSurfer was used to extract subject’s anatomy, which is not my case, since I used CAT12. If those matrices are not present, as comment of line 88 says:

% If available, 1) project scouts on template, 2) project left-right, 3) project back to subject

I guess the projection on the default subject anatomy return some scout vertices both on left and right hemisphere, returning a delocalization of the selected scout.

Is there a way to bypass this problem, since I have in the cortex low surface the Structures of Left and Right hemispheres?

Thanks in advance,

Zanchi

2

You can do the Subject-to-Default scout projections manually to pinpoint the trouble.

  1. Projejct your Subject scout to the Default anatomy
    Open the Subject surface and the Atlas with Scout, then in the Scout tab:
    Scout > Project to... > Default anatomy > EQUIVALENT_SURFACE

  2. Check the projected Scout:
    Open the Default surface and the Atlas with Scout

  3. If there are elements of the Scout that are in both hemispheres
    From the Structures Atlas in the Default anatomy, copy both hemisphere scouts to the Atlas with the projected scout.
    Select the Scout and the Hemisphere where it belongs, and use the menu:
    Scout > Intersect, this will compute an AND for the scouts, so leaving only the vertices in the scout you need.

  4. Contralateral project on the Default anatomy

  5. Project the contralateral scout back to the Subject. Check this projected scout, and if the Scout has vertices in both hemispheres, you can do Step 3.