[FieldTrip] beamformer results smaller than brain

[Stolk, A.]

Hi Akiko, I'm not sure whether this is causing it, but w hat size inwardshift did you use when preparing your sourcemodel? Also check this page on our wiki: http://fieldtrip.fcdonders.nl/example/create_single-subject_grids_in_individual_head_space_that_are_all_aligned_in_mni_space Best, Arjen ----- Oorspronkelijk bericht -----
> Van: "Akiko Ikkai" <akiko.ikkai at gmail.com>
> Aan: fieldtrip at donders.ru.nl
> Verzonden: Donderdag 29 maart 2012 00:22:46
> Onderwerp: [FieldTrip] beamformer results smaller than brain
> Hi Fieldtrip users,
> I'm hoping that someone could give me advice on segmentation and
> beamformer on EEG data. I have EEG data set based on 128 channel cap.
> Thanks to the help I got in mid-Feb, I'm now able to create a decent
> segmentation (seg_results image attached) and volume conduction model.
> However, when I run beamformer based on these models, resulting
> beamforming image is often smaller than the brain (beamformer_result
> attached). Particularly posterior parietal and occipital map is NaN. 
> I have tried going back to segmentation and expanded brain by
> using imdilate after ft_volumesegment such as:
> newbrain = imdilate(seg2.brain,strel_bol(1)); % seg2.brain is original
> brain tissue from segmentation
> seg2.brain = newbrain;
> seg2.seg = seg2.scalp + seg2.skull*3 + seg2.brain*6;
> and run ft_prepare_mesh_new on seg2. Of course, I have to make sure
> there is no intersect between different tissue types, so using
> imdilate has limitation. 
> Could someone explain why this shrinkage might be happening, and how I
> could fix it? 
> Thanks in advance! Akiko
> --
> Akiko Ikkai, Ph.D.
> Postdoctoral Fellow
> Department of Psychological and Brain Sciences
> Johns Hopkins University
> Ames Hall, 3400 N. Charles St.
> Baltimore, MD 21218
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