Yes. That's pretty much what I wanted to say.
Best regards,
-John
2011/5/4 Pablo Ripollés Vidal <[log in to unmask]>:
> Hi,
> Thank you again for your answer. So if I have understood well, the fact that
> I get smaller rms for U.Segmentation than for Dartel does not necessarily
> mean that the first has achieved a better registration of the image with the
> simulated lesion than the latter. It could be just due to the small
> deformation approach used by U. Segmentation which yields smaller
> differences between the deformation fields. Am I rigth??
>
> Thanks again and best regards,
>
>
>
> 2011/5/4 John Ashburner <[log in to unmask]>
>>
>> I understand a bit better now. Your results are probably what would
>> be expected in that the smallest deformations are likely to be the
>> most similar to each other. Dartel is less heavily regularised than
>> the old basis function approaches, so the differences between
>> deformations estimated using different data are likely to be smaller.
>> Your approach to validation will therefore give some information about
>> registration accuracy and reproducibility, but it does not tell the
>> whole story. For example, consider an approach that involves not
>> registering them. This would result in identical deformations (ie
>> identity transforms) for both images, resulting in the least possible
>> difference between them. It wouldn't mean that it is necessarily a
>> good approach though.
>>
>> Best regards,
>> -John
>>
>> 2011/5/3 Pablo Ripollés Vidal <[log in to unmask]>:
>> > Thank you very much for your quick answer, Dr Ashburner.
>> > It is the same subject with and without a simulated lesion. The ground
>> > truth
>> > its the estimated deformation of the subject without the lesion.
>> > Best regards,
>> >
>> > 2011/5/3 John Ashburner <[log in to unmask]>
>> >>
>> >> 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.
>> >> >
>> >
>> >
>> >
>> > --
>> > Pablo Ripollés Vidal
>> > Ph.D Student
>> > Cognition and Brain Plasticity Unit http://www.brainvitge.org/
>> > IDIBELL [Bellvitge Biomedical Research Institute]
>> > L’Hospitalet de Llobregat, Barcelona, 08097,Spain
>> >
>
>
>
> --
> Pablo Ripollés Vidal
> Ph.D Student
> Cognition and Brain Plasticity Unit http://www.brainvitge.org/
> IDIBELL [Bellvitge Biomedical Research Institute]
> L’Hospitalet de Llobregat, Barcelona, 08097,Spain
>
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