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I don't quite understand what you are doing.  Are these T1s from two
different subjects? Do you have some form of ground truth with which
to compare the estimated deformations?

Best regards,
-John


On 3 May 2011 18:39, Pablo Ripolles <[log in to unmask]> wrote:
> Hello SPMrs,
> I am trying to compare deformation fields from 2 different T1s after being normalized with DARTEL and Unified Segmentation. After unified segmentation has run I get the deformation field from the .mat with the deformation utility. I do the same after Create Dartel has finished getting the def field from the flow field. Then I calculate the root mean square difference from voxels in the defformation field from image 1 and image 2 first for U.Segmentation and then for Dartel. What I want to see is which of the 2 algorithms performs better.
>
>
> From recent results in papers I expect DARTEL to outperform unified segmentation (Klein et al, 2009) but this only happens when I take the mean rms of all the voxels in the deformation fields. When I calculate the mean root square difference for only the voxels from the defformation field which belong to brain, unified segmentation outperforms DARTEL. For def fields obtained from unified segmentation I use the brainmask provided with SPM8 to use only "brain voxels" and for def fields from DARTEL I use a mask obtained from the Template calculated by the algorithm .
>
>
> As unified segmentation uses a small deformation approach and DARTEL a large deformation framework, are the results from de mean square roots comparable?Am I doing something wrong?
>
>  I would really appreciate some help.
>
> Thanks to everyone in advance.
>