Hi James,
It probably wouldn't make much difference -but I'm not really sure. Taking logs of the Jacobian differences produced by the toolbox certainly wouldn't work though.
All the best,
John
James Cole <[log in to unmask]> wrote:
>Hi John, Ged & other SPM doyens,
>
>I've used the pairwise registration procedure as proposed by John in some previous posts, and it works nicely. A few questions:
>
>I ran group comparisons based on the Jacobian determinant images, though I've read in a couple of places that it would be better to use the log Jacobian instead or perhaps the divergence images. Does this make a big difference?
>
>In the Frontiers paper from 2013 (Symmetric diffeomorphic modeling of longitudinal structural MRI), you plot the main eigenvectors from the divergence maps, via the Gram matrices. Do you have any code or tips on how to implement this? It's a good way to visualise individual's trajectories.
>
>Also in that paper, the mean expansion rate were computed for each subject, by fitting voxel-wise linear models through the divergence maps. Again, I'm not sure how to actually go about doing this; do you have any code or advice to run this in SPM?
>
>Thanks for the help,
>James
>
>James H Cole, PhD
>
>C3NL
>
>Division of Brain Sciences
>
>Department of Medicine
>
>Imperial College London
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