beamformer source localization for EEG

Mark Drakesmith mark.drakesmith at POSTGRAD.MANCHESTER.AC.UK
Thu Jul 9 16:29:41 CEST 2009


I ran into the same problem with strel_bol when trying to create a BEM
model. It relies on a custom script which implements the strel command
in the image processing toolbox.

The script can be found in the message archives here:




Mark Drakesmith
PhD Student

Neuroscience and Aphasia Research Unit (NARU)
University of Manchester

Andrei Medvedev wrote:
> Dear Fieldtrip developers/users
> I am a relatively recent user of Fieldtrip (and very much appreciative of this software). Having good experience with the analysis of brain oscillations etc, I now want to proceed with source reconstruction and it appeared that I need some help with the beamformer technique for EEG data. I am trying to use it for EEG data collected with a 128-channel EGI system. I also have structural MRI data for my subjects and would like to use realistic head models etc. I was following the Fieldtrip tutorial (1) “Localizing oscillatory sources using beamformer techniques”, which applies this method to MEG data. My understanding is that the only difference I would make when applying this approach to EEG is that, instead of the command
> vol = prepare_singleshell(cfg, segmentedmriF);
> which implements Nolte’s approach for MEG data, I need to make a BEM model for EEG data and I thought that I could use an example Matlab script (2) “Create BEM headmodel for EEG” from the Fieldtrip site. This would give me a vol variable which I then use to calculate the grid variable using
> [grid] = prepare_leadfield(cfg);
> and the rest is the same as in tutorial (1).
> Q1. Is it a correct sequence of steps to do source reconstruction for EEG data in Fieldtrip or do I need to do something more different?
> Q2. My second question is about the function strel_bol() which I am not familiar with (it is used in script (2)). One can see from the script that it is a structural element function used in the Image Processing toolbox but this toolbox has only function strel(). Could you please explain what the strel_bol(5) is? Can it be replaced by something like strel('disk',5)?
> Your help is very much appreciated!
> Thank you,
> Andrei.
> Andrei Medvedev, PhD
> Assistant Professor,
> EEG and Optical Imaging Lab
> Center for Functional and Molecular Imaging
> Georgetown University
> Washington DC, 20057

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