Dear SPM-community,
I followed your recent discussion about within and between sessions realignment
with great interest. And it raised a question concerning a study we are
conducting.
We have a design consisting of four sessions. Sessions A and B are aquired
together in one examination, whereas sessions A' and B' are also aquired
together a week later. In order to compare sessions A/A' and B/B', I put all
four sessions in one model. My understanding was that the realignment algorithm
would account for the differences in position and orientation and realigns all
images to the first image of the first session. I believed that this should
work regardless of whether the sessions were acquired all at once or whether
several delayed examinations were involved.
It is quite certain, that the position of the subject's head in the scanner
differs considerably between examination 1 (sessions A an B) and examination 2
(session A' and B'), conducted several days later.
Now, are my assumptions correct or should I be concerned about the adequacy of
the image coregistration between sessions ?
Thanks in advance for any comments.
Regards,
Tobias Flaisch
Dep. of Psychology
University of Konstanz
P.O Box D25
D-78457 Konstanz, Germany
Phone +49 (0)7531 88-4706
Fax: +49 (0)7531 88-2891
e-mail: [log in to unmask]
http://www.clinical-psychology.uni-konstanz.de/
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