[FieldTrip] Question on forward modeling

["Jörn M. Horschig"]

Hi Kidist,


On 10/16/2013 3:30 PM, kgm at tf.uni-kiel.de wrote:
> Hello,
>
> I am trying to do forward modeling using individual MRI and MEG from
> Neuromag306 system. I have three questions.
>
> I have performed the following steps:
>
> 1. ft_read_mri
> 2. ft_volumerealign
> 3. ft_volumesegment
>     Q1. At this point I want to check if the segmentation fits the MRI
> correctly. So I used ft_sourceplot but I am getting the following
> message with an empty plot:
> the input is segmented volume data with dimensions [256 256 176]
> scaling anatomy to [0 1]
> no functional parameter
> no masking parameter
> the call to "ft_sourceplot" took 4 seconds

Hard to tell, maybe post a snippet of your cfg? First, however, you 
might want to have a look at this tutorial and especially check how the 
segmented mri is plotted and what else is done:
http://fieldtrip.fcdonders.nl/tutorial/beamformingextended#preparing_the_data_and_the_forward_and_inverse_model

> 4. ft_prepare_headmodel, method: singleshell
> 5. ft_plot_sens and ft_plot_vol, after converting the units
>     Q2. The plot shows that the sensors/electrodes are quiet far away from
> the brain. Is there a means to do some projection to lower them a bit?
> Or is the problem arising from the co-registration? I have attached the
> figure.
Most likely, this is indeed a problem with the co-registration, or the 
subject was just seated that way. You mustn't just project sensors to 
make the plot appeal better to you ;)

>     Q3. I have also used 'localspheres' method to prepare the head model.
> The output of the plot (attached) gives me some rounded image which
> does not look like a brain. Is there another function used to plot the
> local spheres?
My guess is that you need to reduce the radii of the localspheres. Looks 
like they are defined in cm while the rest of your anatomy is defined in 
mm.


Best,
Jörn

>
> Looking forward for the response.
>
> Best regards,
>
> Ms.c. Kidist G.Mideksa
> Department of Neurology,
> Uni-Klinikum, Kiel, Germany
>
>
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-- 
Jörn M. Horschig
PhD Student
Donders Institute for Brain, Cognition and Behaviour
Centre for Cognitive Neuroimaging
Radboud University Nijmegen
Neuronal Oscillations Group
FieldTrip Development Team

P.O. Box 9101
NL-6500 HB Nijmegen
The Netherlands

Contact:
E-Mail: jm.horschig at donders.ru.nl
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