[FieldTrip] Dimension of lead-field Matrix

pooneh baniasad pooneh.baniasad at gmail.com
Mon Oct 10 13:55:02 CEST 2016


Dear Simon

Thanks a lot for your attention and sorry for the late response. I've
actually found which part of the code makes a problem. I used the
ft_prepare_vol_sens's function in a wrong way.

Now I have another problem. I change the coordination system from 'ctf' to
'spm' by using this code:

cfg = [];

[mri] = ft_volumenormalise(cfg, mri);

When I segmented 'scalp' separately and prepared mesh from it, the figure
was well (1.fig). On the other hand when I changed the segmentation into
{'brain', 'skull', 'scalp'}, the scalp can not be computed properly
(2.fig).

On Mon, Oct 3, 2016 at 4:57 PM, Simon Homolle <s.homolle at donders.ru.nl>
wrote:

> Dear Pooneh,
>
> http://www.fieldtriptoolbox.org/tutorial/headmodel_eeg_bem
>
> I relate to this part:
>
>
>  When the forward solution is computed, the lead field matrix (= channels
> X source points matrix) is calculated *for each grid point* taking into
> account the head model and the channel positions.
>
>
> So I assume your mesh consists of 2000 grid points?
>
> Simon Homölle
> PhD Candidate
> Donders Institute for Brain, Cognition and Behaviour
> Centre for Cognitive Neuroimaging
> Radboud University Nijmegen
> Phone: +31-(0)24-36-65059
>
> On 03 Oct 2016, at 13:01, pooneh baniasad <pooneh.baniasad at gmail.com>
> wrote:
>
> Dear Simon,
>
> I've followed this tutorial:
> http://www.fieldtriptoolbox.org/tutorial/headmodel_eeg_bem to construct
> the headmodel ('VolBEM')
> I use 'standard_1020.elc' for 'elec' and 'cortex_20484.surf.gii' for
> 'DipPos'.
> Is it clear or should I explain more? ūüôā
>
> On Mon, Oct 3, 2016 at 11:53 AM, Simon Homolle <s.homolle at donders.ru.nl>
> wrote:
>
>> Dear pooh,
>>
>> Could you provide more information how you constructed your BEM-model?
>>
>> best regards,
>>
>> Simon Homölle
>> PhD Candidate
>> Donders Institute for Brain, Cognition and Behaviour
>> Centre for Cognitive Neuroimaging
>> Radboud University Nijmegen
>> Phone: +31-(0)24-36-65059
>>
>> On 02 Oct 2016, at 12:22, pooneh baniasad <pooneh.baniasad at gmail.com>
>> wrote:
>>
>> Dear FieldTrip community
>>
>> I'm using the forward model to simulating EEG signal although it seems
>> the dimension of the lead-field matrix is not correct. Here is a review of
>> the procedure.
>>
>> First I constructed a BEM headmodel for EEG source analysis ‚Äčand then by
>> loading the template cortex, I put the dipoles with specific current source
>> on that. I expect the dimension of the lead-field matrix will be m*n which
>> m=electrode's number and n=3*dipole's number but 'm' is different.
>> Since I used the template electrode 'standard_1020.elc', m = 97 according
>> to:
>>
>>   chanpos: [97x3 double]
>>     chantype: {97x1 cell}
>>     chanunit: {97x1 cell}
>>      elecpos: [97x3 double]
>>        label: {97x1 cell}
>>         type: 'eeg1010'
>>         unit: 'mm'
>>
>> while the dimension of lead-field matrix is:  2000x122880
>>
>> I use this function for calculating lead-field matrix:
>>
>> LF = ft_compute_leadfield(DipPos, elec, VolBEM);
>> ‚ÄčI do not understand why the number of raws are different‚Äč!
>>
>> ‚ÄčOn the other hand I guess that there is a similarity between the number
>> of raws in the volume head model and LF matrix due to the dimension of
>> headmodel matrix is: 2000x8000 double .‚Äč
>>
>> ‚ÄčI will be so thankful if anyone can help me.‚Äč
>>
>> --
>> Bests
>>
>> Pouneh Baniasad
>> _______________________________________________
>> fieldtrip mailing list
>> fieldtrip at donders.ru.nl
>> https://mailman.science.ru.nl/mailman/listinfo/fieldtrip
>>
>>
>>
>> _______________________________________________
>> fieldtrip mailing list
>> fieldtrip at donders.ru.nl
>> https://mailman.science.ru.nl/mailman/listinfo/fieldtrip
>>
>
>
>
> --
> Bests
>
> Pouneh Baniasad
> _______________________________________________
> fieldtrip mailing list
> fieldtrip at donders.ru.nl
> https://mailman.science.ru.nl/mailman/listinfo/fieldtrip
>
>
>
> _______________________________________________
> fieldtrip mailing list
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> https://mailman.science.ru.nl/mailman/listinfo/fieldtrip
>



-- 
Bests

Pouneh Baniasad
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