[FieldTrip] lead field with no MRI
rapela at ucsd.edu
Sun May 29 21:38:50 CEST 2011
Below I describe how to compute the leadfield matrix adjusted to a set of
electrodes in an extended 10-20 system, without having an MRI image.
Besides, I have a question: why in the help of the fieldtrip functions
their output is not described?
I had to dig into the EEGLAB Dipfit plugin to learn how to do this. I used
the function ft_prepare_leadfield. It requires a head model and the
channel locations. Since I have an extended 10-20 electrode system, I used
a BEM head model that comes with Dipfit, and also uses an extended 10-20
system. This head model is in the plugins directory of dipfit2.2:
and the channel locations for this head model are also in the dipfit2.2
It turns out that the previous head model is not ready for
ft_prepare_leadfield, and I had to use the function ft_prepare_vol_sens
to prepare it. Also, I wanted to compute the leadfield matrix only for the
channels in my data set, whose labels are in the variable dsChanlabels, so
I passed dsChanlabels as the argument 'channel' of ft_prepare_vol_sens.
Finally, I used the head model and sensors prepared by ft_prepare_vol_sens
as input to ft_prepare_headmodel. I append the code that does the job. If
you see any bug, please let me know.
function grid = joacosPrepareLeadfield(dsChanlabels, hmChanfile, hdmFile)
cfg = ;
vol = ft_read_vol(hdmFile);
sens = ft_read_sens(hmChanfile);
[vol, sens] = ft_prepare_vol_sens(vol, sens, 'channel', dsChanlabels);
cfg = ;
cfg.elec = sens;
cfg.vol = vol;
cfg.grid.resolution = 20;
data = ;
grid = ft_prepare_leadfield(cfg, data);
> Dear all,
> I want to compute a lead field matrix but I have no MRI scan of my
> subjects. I would be happy with a concentric spheres model, or similar,
> adjusted to the electrodes locations (modified 10 20 system). I would be
> very grateful if somebody directs me to the appropriate functions in
> FieldTrip. My apologizes if this is a naive question. I am new to
> Thanks in advance, Joaquin
> Joaquin Rapela, PhD
> Swartz Center for Computational Neuroscience
> University of California San Diego
> 9500 Gilman Drive,
> San Diego, CA 92093-0559
> tel/fax: (858) 822-7536
> There are men who struggle for a day and they are good.
> There are men who struggle for a year and they are better.
> There are men who struggle many years, and they are better still.
> But there are those who struggle all their lives:
> These are the indispensable ones.
> fieldtrip mailing list
> fieldtrip at donders.ru.nl
Joaquin Rapela, PhD
Swartz Center for Computational Neuroscience
University of California San Diego
9500 Gilman Drive,
San Diego, CA 92093-0559
tel/fax: (858) 822-7536
There are men who struggle for a day and they are good.
There are men who struggle for a year and they are better.
There are men who struggle many years, and they are better still.
But there are those who struggle all their lives:
These are the indispensable ones.
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