Hi Laurence,
This transform indeed just aligns the volume and sensors to MNI space
but does not rescale them since forwinv code will not allow rescaling
MEG sensors. So it is MNI space in terms of origin and axes but the
results should be interpreted using the individual structural
coregistered to the template rather than the template itself. I don't
remember what I did at the end. If I projected the locations to the
template MNI space then they do correspond to the template.
Vladimir
Sent from my iPad
On 12 Oct 2010, at 20:11, Laurence Hunt <[log in to unmask]> wrote:
> Hi Vladimir,
>
> I've been playing with the script you wrote for the M/EEG toolbox using fieldtrip to fit single dipoles - it's certainly saved me a lot of time! There's one thing I don't quite understand in the calling of ft_transform_vol (and the subsequent projection of the fitted dipole back to MNI space) that I was hoping you could help me with . Instead of using datareg.toMNI to project the volume conduction model and sensor layout, you define a new matrix, M1, that seems to me to preserve the translation elements of datareg.toMNI (last row and column) but remove any scaling that the matrix would perform.
>
> (a) Am I right in thinking that this is what
>
> [U,L,V] = svd(M1(1:3,1:3));
> M1(1:3,1:3) = U*V';
>
> achieves?
>
> (b) If so, why does the rescaling have to be removed? What space does M1 project the model and sensor layout to?
>
> Many thanks,
> Laurence
>
>
> ===========================================
> Laurence Hunt, DPhil Student
> Centre for Functional MRI of the Brain (FMRIB),
> University of Oxford
> [log in to unmask]
> Phone: (+44)1865-(2)22738
> ===========================================
>
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