Hi - yes, FEAT5 does indeed allow you to analyze unbalanced designs, but
in fact, that's not really the point here:
The first thing to note is that changing TR from 0.2 to 0.6s probably
won't have a huge impact anyway on the baseline and activation BOLD
signal. However, in any case, any effect would largely be a scaling of
both baseline and activation signal change, so the
percentage-change-activation would be the same, ie the grand-mean (4D)
intensity normalisation that FEAT always carries out in the preprocessing
would rescale the baseline AND the activation signal so that it is
comparable across subjects.
So - you should hopefully be safe in your analysis.
Thanks, Steve.
On Mon, 13 Jan 2003, Martin Kronbichler wrote:
> Dear FSL-Experts,
>
> I´m currently working with some unfortunate data which was acquired with
> non-optimal acquistion parameters. The main problem is that the group, who
> performed the experiment used a PRESTO sequence in which the TR was
> determined individually for each subject.
> So now i have scans with differnet TRs (differences ranging from something
> like 0.2 to around 0,6 secs) from each subject.
> >From a discussion on the SPM mailing list some time ago, i remember that it
> was not possible to analyze these scans because of unequal covariance or
> somenthing like that.
> As i understand it, FSL mixed effect approach allows one to analyze data
> from unbalanced designs, would it also be possible and valid to analyze
> scans with different TRs?
>
> all the best,
>
> Martin
>
> Martin Kronbichler
> Institute of Psychology
> University of Salzuburg
> Hellbrunnerstr. 34
> 5020 Salzburg
> Austria
> tel.: 0662/8044-5162
> fax.: 0662/8044-5126
> e-mail: [log in to unmask]
>
Stephen M. Smith
Head of Image Analysis, FMRIB
Oxford University Centre for Functional MRI of the Brain
John Radcliffe Hospital, Headington, Oxford OX3 9DU, UK
+44 (0) 1865 222726 (fax 222717)
[log in to unmask] http://www.fmrib.ox.ac.uk/~steve
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