Dear Carles,
your proposed steps are ok, but I would suggest the following changes:
- segment all scans in the first/second step without using using customized priors or templates.
The impact of the priors/templates in SPM5 is minimized and you don't need to customize your
priors/templates (except for e.g. children data, where the distribution of GM/WM/CSF deviates
from adult subjects)
- coregister the segmented images
- modulation makes no sense for longitudinal data because you analyze relative differences
between the scans of each subject and there is no need to correct for the volume changes due to
warping, because the warping parameters are the same for all scans of one subject
You might also try the longitudinal segmentation in the VBM2 toolbox which merges all these
steps using the good old SPM2 segmentation:
http://dbm.neuro.uni-jena.de/vbm
The advantage of this approach is that you use the same templates and priors for all scans of one
subject. In SPM5 the templates/priors might be warped differently to the scans, which can cause
artificial differences in segmentation if there are large differences between the scans of one
subject (e.g. atrophy)
Best regards,
Christian
____________________________________________________________________________
Christian Gaser, Ph.D.
Assistant Professor of Computational Neuroscience
Department of Psychiatry
Friedrich-Schiller-University of Jena
Philosophenweg 3, D-07743 Jena, Germany
Tel: ++49-3641-935805 Fax: ++49-3641-935280
e-mail: [log in to unmask]
http://dbm.neuro.uni-jena.de
On Tue, 26 Sep 2006 11:53:31 +0200, CARLES M. FALCON FALCON <[log in to unmask]> wrote:
>Dear Spmers,
>
>I have some doubts abouts how to do a longitudinal VBM with SPM5.
>
>What I was planning to do is
>- to segment the first scans using the default priors to create my own GM, WM
>and CSF priors,
>- to segment the first scans again using my own GM,WM and CSF priors and
>writing modulated and unmodulated normalized segmented images,
>- to coregister the second scan to the first one,
>- to segment the second scan and write segmented images in the native space,
>- to apply the normalization parameters of the first scans, obtained in
>segmentation step, to the second segmented scans
>- to smooth the images.
>In this case, to create my own template doesn't seem necessary, just the
>priors.
>
>The first question is if this procedure is suitable and the most adequate. The
>second question is how to change normalize writing options (voxel size) when
>creating normalized segmented files from segment function.
>
>Any advice on these questions would be much appreciate.
>
>Thanks
>
>Carles Falcon
>IDIBAPS-Hospital Clinic Barcelona
>University of Barcelona. SPAIN
>
>
>
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