Dear Christopher,
the simple answer is: you should use ArtifactRepair/TSDiffAna/some other
tool to assess the quality of your data, but you should never attempt to
"repair" your time series by removing/replacing slices/scans. If there
are technical reasons for bad image quality, you should improve your
setup and scan again. If there is head movement in some subject that
severely distorts your data, you should scan another subject. If head
movement is due to your experimental design, you should check whether
the design, experiment setup and subject instructions can be improved.
The only acceptable reason for "repairing" bad data would be that your
individual subject has very special abilities that can not be found in
any other subject. There is a tutorial for ArtifactRepair at
http://cibsr.stanford.edu/tools/ArtRepair/ArtRepair.htm
which discusses the available options and their pros and cons.
Volkmar
Am Mittwoch, den 17.12.2008, 01:22 +0000 schrieb Christopher Benjamin:
> Hi,
>
> I didn't receive a response to this post; apologies for re-posting if this is quite basic but
> I'm having trouble finding a practical discussion of these issues. Any help would be
> invaluable,
>
> With thanks,
>
> Chris
>
> ---------------------------
>
> Hi Spmmers,
>
> I'm removing artefact from event-related fMRI data using Sue Whitfield Gabrieli's
> automated artifact detection toolbox (http://web.mit.edu/swg/software.htm).
>
> I'm wondering if people are using any standard criteria for removal of images in terms of
> -
>
> 1. Image signal variation (i.e., deviation of signal from the series mean);
> 2. Participant movement, and
> 3. Participant rotation.
>
> In terms of criteria I've seen,
> 1. often seems to be used to exclude images that deviate from the mean by more than
> two or three standard deviations; (which I think makes sense);
> 2. to exclude images in which movement beyond .5 or 1mm occurred, and for
> 3. exclusion of iamges where rotation of more than .05 radians occurred.
>
> I realise there are unlikely to be rigid criteria, especially given the limitations inherent in
> scanning some populations, but I'd greatly appreciate anyone point me to a stand-out
> reference/discussion...
>
> With thanks
>
> Christopher
>
--
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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