Hi,
I would normally say that this is because you haven't removed the
first few scans, and the MRI data has not yet reached steady-state -
there's a button under the "data" tab in FEAT for telling FEAT to
remove these scans - don't forget to adjust your model accordingly
(see the manual for more details).
However, this normally results in the first few scans being HIGHER
not lower than the rest. You should check (using timeseries view in
FSLView) whether this is present in the original data or a result of
the preprocessing - but nothing obvious springs to mind from the
processing that would explain this?
Cheers, Steve.
On 31 Jul 2007, at 16:48, Vishwadeep Ahluwalia wrote:
> Hi,
> I plotted the mean time series extracted from filtered_func image
> within
> different ROIs and found that the first two values of each time
> series is
> way less than the consequent values. I'm assuming this is done on
> purpose
> and is not an artifact. Can anyone tell me why this is done and what
> pre-processing step causes this decrease? Thanks!
> -Vish
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Stephen M. Smith, Professor of Biomedical Engineering
Associate Director, Oxford University FMRIB Centre
FMRIB, JR 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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