[FieldTrip] problem with MEG leadfield

[s.rombetto at cib.na.cnr.it]

Thank you Hamid and Lilla

your observations were correct and I solved my problem :-)

Thanks for helping

Best regards
Sara

> Hi,
>
> In MEG normally people use single layer volume conductor and It
> is believed that three layer is not useful and can deteriorate the results
> (this is in contrast to EEG). Therefore,  you should use a single shell or
> a single sphere for MEG, which models only the brain (conductivity of the
> scalp is assumed to be same as the air).
>
> Thanks
>
>
>
>
> On 10 March 2013 17:22, <s.rombetto at cib.na.cnr.it> wrote:
>
>> Hi everybody
>> I'm trying to generate a field for a simulated dipole using the command
>> ft_dipolesimulation, for a MEG study.
>>
>> I do the following:
>> -read the hdr
>>
>> -import the sensor structure with the following lines
>> grad=hdr.grad;
>> radius = sqrt(sum(grad.chanpos.^2,2));
>> grad.chanpos = grad.chanpos./ [radius radius radius];
>> grad.label=hdr.label(1:306)';
>>
>> -then I create the vol structure using the following code
>> vol = [];
>> vol.r = 12 * [0.88 0.92 1.00]; %   radii of spheres, the head radius is 12
>> cm
>> vol.c = [1 1/80 1];       % conductivity
>> vol.o = [0 0 0];
>>
>> At this point I have the grad structure, and the vol structure.
>> Then I give all the options for the dipole simulation with the code
>>
>> %% create a dipole simulation with a custom timecourse
>> cfg      = [];
>> cfg.vol  = vol;      % see above
>> cfg.grad = grad;     % see above
>> cfg.dip.pos = [0 0.5 0.3];
>> cfg.dip.mom = [1 0 0]';
>> cfg.dip.frequency = 10;     %Hz
>> cfg.ntrials = 10;
>> cfg.triallength = 20;        % seconds
>> cfg.fsample = 250;          % Hz
>>
>> but when I try to esecute the line
>>
>> raw1 = ft_dipolesimulation(cfg);
>>
>> I find this error
>>
>> ??? Error using ==> ft_compute_leadfield at 301
>> unsupported volume conductor model for MEG
>>
>> Error in ==> ft_dipolesimulation at 198
>>   lf = ft_compute_leadfield(dippos{**trial}, sens, vol);
>>
>>
>> I really cannot understand why  volume conductor model is not supported.
>> Any suggestion? I'm pretty sure that the mistake is trivial, but I'm not
>> able to see it.
>>
>> Thank you!
>> Dott.ssa Sara Rombetto
>>
>>  Istituto di Cibernetica
>>  "E. Caianiello"
>>  Via Campi Flegrei, 34
>>  80078 Pozzuoli (NA)
>>  Italy
>>  mob +39 3491530515
>>  tel +39 0818675361
>>  fax +39 0818675128
>>
>>
>> "I disapprove of what you say, but I will defend to the death your right
>> to say
>> it." [Evelyn Beatrice Hall, The Friends Of Voltaire]
>>
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>>
>>
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>>
>
>
>
> --
> Hamid R. Mohseni, PhD
> Post-Doctoral Research Assistant
> Institute of Biomedical Engineering
> University of Oxford, OX3 7DQ, UK
> Tel: +44 (0) 1865 2 83826
>



-------------------------
  Dott.ssa Sara Rombetto
  Istituto di Cibernetica
  "E. Caianiello"
  Via Campi Flegrei, 34
  80078 Pozzuoli (NA)
  Italy
  mob +39 3491530515
  tel +39 0818675361
  fax +39 0818675128
--------------------------
"I disapprove of what you say, but I will defend to the death your  
right to say
it." [Evelyn Beatrice Hall, The Friends Of Voltaire]

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