The realignment includes the option of aligning multiple sessions (runs)
of the same subject together. I'm pretty sure I said this in the
manual, but if not, then here is the basic idea...
* Each run/session is aligned with the first image in the session.
* Then all the first images are aligned together.
* Rigid-body transforms are then composed appropriately.
The idea is to achieve (hopefully) more accurate within session
alignment, while aligning the sessions together.
Best regards,
-John
On Wed, 2009-11-04 at 11:32 +0000, Stancak, Andrej wrote:
> Dear members of SPM community:
>
> We have acquired functional MR images from three consecutive sessions each counting 256 volumes. However, the consecutive sessions were separated by about 1.5 hour break meaning the subjects were taken out of the scanner after each session. The question is how to realign the images: should we realign and later coregister/normalise each session as if each session would be a separate experiment or should we realign all three sessions using one realignment. We tried the latter and found almost no spatial drifts within each of three sessions but about 5 mm displacements in head position between the three sessions. I would be grateful for a hint whether we should realign images in each session separately or rather concatenate the three sessions.
>
> Best wishes
> Andrej Stancak
>
> Andrej Stancak, PhD.
> Professor for normal physiology
> Senior lecturer in psychology
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John Ashburner <[log in to unmask]>
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