[FieldTrip] left to right inversion after source interpolation

[Kathrin Müsch]

Dear Fred,

I encountered a similar thing a while ago and it was because spm8 seems to plot in radiological convention (i.e. left is plotted right and vice versa - http://mailman.science.ru.nl/pipermail/fieldtrip/2012-May/005229.html) so you're plots should actually be correct.

If you use cfg.interactive = 'yes'; and click into the activated side of the brain, the first coordinate should be negative because you are in the left hemisphere.

Hope that helps,
Kathrin


Am 05.09.2012 um 14:47 schrieb Frederic Roux:

> Dear fieldtrip users,
> 
> I have noticed that after interpolating a dummy source volume with ft_sourceinterpolate,
> voxels that were located in the left side of the volume, apear to be located in the right
> side of the volume.
> 
> The code that I use is as following:
> 
> dummy is a dummy structure of an lcmv beamformer map with the fields
> 
> dummy =
> dim :        [15 18 17]
> time:        [1x272662 double]
> pos:         [4590x3 double]
> inside:     [1x2144 double]
> outside:   [1x2446 double]
> method: 'average'
> avg: [1x1 struct]
> 
> voxpos = dummy.pos(dummy.inside,1);% get the coordinates of voxels inside the volume
> dummy.avg.pow(dummy.inside(sign(voxpos)==1)) = 0; % set activity in the left hemisphere to 0
> dummy.avg.pow(dummy.inside(sign(voxpos)==-1)) = 1; % set activity in the left hemisphere to 1
> 
> cfg = [];
> cfg.parameters = 'all';
> 
> int_dummy = ft_sourceinterpolate(cfg,dummy,template_MNI_mri);
> 
> cfg = [];
> cfg.funparameter = 'avg.pow';
> cfg.method = 'ortho';
> 
> %plot the non-interpolated volume
> figure;
> ft_sourceplot(cfg,dummy);
> 
> %plot the interpolated volume
> figure;
> ft_sourceplot(cfg,int_dummy);
> 
> As you can see from the figure in the attachement, the voxels that
> corresponded to the left hemisphere prior to the interpolation,
> no appear to be located in the rigth hemisphere.
> 
> This is also something that I have observed in real data.
> 
> Does anybody have an explanation why this is happening?
> Am I doing something wrong?
> 
> Best,
> 
> Fred
> 
> 
> <non_interp_vs_interp.jpg>_______________________________________________
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