[FieldTrip] anatomical labelling of dipole positions

[Eelke Spaak]

Hi Tom,

ft_volumenormalise will allow you to normalise an anatomical volume to
MNI space. The output of ft_volumenormalise will have a .params and
.initial field. These you need, you can discard the actual normalised
volumetric data. The fields contain the linear (.initial) and
nonlinear (.params) warps needed to go from subject-specific to MNI
space, and vice versa. Using these you can do something like:

normalised = ft_volumenormalise([], mri);
mnipos = ft_warp_apply(normalised.params,
ft_warp_apply(normalised.initial, subjectpos), 'individual2sn');

where subjectpos is an Nx3 array of subject-specific coordinates, and
mnipos will of course be Nx3 in MNI space.

In case of questions we can discuss tomorrow in person :)

Best,
Eelke

On 26 August 2014 17:49, Tom Marshall <t.marshall at fcdonders.ru.nl> wrote:
> Hi Trippers,
>
> I have performed dipole fitting on some data and I would like to identify
> the anatomical regions in which various dipoles are located - ie, to make
> statements of the sort, 'dipole X was (best) localised to the right superior
> parietal cortex'. Specifically - I have the output from ft_dipolefitting
> which gives positions in the head space of the individual subjects, and I
> would like to anatomically label the dipoles according to the AAL atlas,
> which is based on the MNI template brain.
>
> I *think* what I will need to do is apply some warping of the subject MRI to
> the MNI template, and then apply the same warping to the dipole co-ordinate.
> However it is not clear to me how to warp a single point, rather than an
> entire volume. Is there some fieldtrip function that could be used for this?
>
> I do not think the approach detailed in
> <http://fieldtrip.fcdonders.nl/example/create_single-subject_grids_in_individual_head_space_that_are_all_aligned_in_mni_space>
> will be much use here, since (if I understand correctly) the MNI-aligned
> grid created here would only be used as a starting point for
> ft_dipolefitting. In the end a given dipole might not correspond to any grid
> point.
>
> Can anybody advise me on how to set about this?
>
> Thanks a lot.
>
> Best,
> Tom
>
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