[FieldTrip] Problem averaging sources ("vary in the field 'inside'")

[Constantino Méndez Bértolo]

Dear Tzvetan,
Thank you very much, it worked like a charm: substituting .dim and .pos for
the one in our template, then averaging and then interpolating.
May the gods of beamformer always light up your way,
T


2014-12-03 16:55 GMT+01:00 Tzvetan Popov <tzvetan.popov at uni-konstanz.de>:

> Peace T,
> this is due to the unnecessary interpolating and normalizing back and
> forth where due to some edge irregularities you end up with slightly
> different inside fields. Using mni aligned grids is actually meant to
> circumvent the need for normalizing etc.
> In general you should use ft_sourceinterpolate in order to visualize 1).
> single subject data (this worked for you) 2). output data from
> ft_sourcegrandaverage or 3) output from ft_sourcestatistics. Because you
> are using the mni template approach you’ll never use ft_volumenormalize in
> your pipeline. So in order to make 2) and 3) work you should exchange the
> single subject source.dim and source.pos fields with template_grid.dim and
> template_grid.pos respectively. Subsequently you can call
> ft_sourcegrandaverage with all your subjects as an input and use the output
> to interpolate onto the mni template brain.
>
> good luck
> tzvetan
>
>
>
> Dear fieldtrippers,
>
> We are doing beamformer with ERF acquired with an Elekta-Neuromag.
> Regardless our different approaches, we always end with the same problem at
> the end of the pipeline - the 'inside' field slightly varies between
> subjects. I attach a plot of the difference between the inside field of two
> different subjects where one can see that there are truly minor differences.
>
> We follow the standard pipeline, I think. We use a template grid and
> template mri for all the subjects, which we realign using individual
> headpoints. The resulting leadfield (every subject has the same numbers of
> dipoles) is used in the sourceanalysis ('lcmv'), and the difference between
> pre and post periods is first interpolated (using the individual mri
> aligned) and finally normalized. We also tried using volumereslice before
> interpolate.
>
> Individual results seem coherent but not matter what we end up with
> different 'inside' fields and sourcegrandaverage complains about that. We
> are using the fieldtrip-20141201 version and if we use
> the fieldtrip-20111101 sourcegrandaverage does not complain about that.
>
> I don't want to make a really complex mail so I leave it here looking
> forward to hear input from anybody and willing to give more precise
> information,
>
> Peace!
> T
>
>
>
> --
> Constantino Méndez-Bértolo
> Laboratorio de Neurociencia Clínica, Centro de Tecnología Biomédica (CTB)
> Parque Científico y Tecnológico de la UPM, Campus de Montegancedo
> 28223 Pozuelo de Alarcón, Madrid, SPAIN
>
>  <s5.inside minus s6.inside.jpg>
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-- 
Constantino Méndez-Bértolo
Laboratorio de Neurociencia Clínica, Centro de Tecnología Biomédica (CTB)

Parque Científico y Tecnológico de la UPM, Campus de Montegancedo

28223 Pozuelo de Alarcón, Madrid, SPAIN
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