Dear Mathieu,
a very brief answer: You should remove the first few scans from each
session. Also, you should treat the sessions separately in realignment,
slice timing (if applicable) and statistics. If you would treat your
data as coming from one single session in the model, SPM would not be
able to model e.g. different mean intensities and you would introduce
errors in estimation of temporal autocorrelation and high-pass
filtering.
Hope this helps,
Volkmar
Am Mittwoch, den 05.11.2008, 19:39 +0100 schrieb Mathieu d'Acremont:
> Dear SPM users,
>
> I'm analyzing fMRI data with SPM8b. Data were recorded during 4
> functional sessions and 1 structural session:
>
> - session 1, functional, 408 vol.
> - session 2, functional, 408 vol.
> - session 3, structural, 192 vol.
> - session 4, functional, 408 vol.
> - session 5, functional, 408 vol.
>
> In each functional session, 4 volumes were recorded before the beginning
> of the task (vol 1-4) and 4 after the end of the task (vol 405-408). So
> only 400 volumes in each functional session are interesting for model
> estimation (vol 5-404).
>
> For model estimation, i want to treat all volumes as if they were coming
> from a unique session (because it is basically the same task in the 4
> functional sessions and i need to simplify the model). I will also use
> the realignment corrections computed during the preprocessing as
> regressors in the model.
>
> I have 2 questions concerning the preprocessing:
>
> - should i define 4 sessions for the realignment or make as if data were
> coming from a unique session?
>
> - which volumes should i delete during the preprocessing (e.g. vol 1-4
> of the first session or of all 4 sessions, what about vol 405-408)?
>
>
> Cheers,
>
--
Volkmar Glauche
-
Department of Neurology [log in to unmask]
Universitaetsklinikum Freiburg Phone 49(0)761-270-5331
Breisacher Str. 64 Fax 49(0)761-270-5416
79106 Freiburg http://fbi.uniklinik-freiburg.de/
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