Dear Venkata,
there a 3 realignment steps in the longitudinal pipeline (see Fig. 4 in the manual):
1. Realignment to calculate mean of realigned T1 images
2. Realignment of all T1 images to that mean image
3. Realignment of native GM segmentations in order to further increase realignment accuracy (works better without scalp and with GM images)
The realigment module in VBM8 is a modified module from SPM8 that also supports weighting of realignment and a so-called halfway realignment to balance out interpolation errors.
Regards,
Christian
On Mon, 16 Jun 2014 12:38:47 +0100, venkata Chaitanya <[log in to unmask]> wrote:
>Dear SPM Experts,
>
> I am doing Preprocessing of Longitudinal data using VBM8 Toolbox(http://dbm.neuro.uni-jena.de/vbm8/VBM8-Manual.pdf). In the above pdf in page no 17, Its given that we have Two Realignments(Realignment1, and Realignment2).
>As far as I understood till now it can be one of these three things.1)Realignment:Estimate 2)Realignment:Reslice 3)Realignment:Estimate&Reslice. It would be great if someone tell me what is Realignment1 and Realignment2 exactly.
>
>Thanks for your help.
>
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