Dear Susana,
you will have a chance to obtain sub-TR resolution if you repeat your
trials using similar stimuli. For each repetition, you would start
stimulus presentation at a different time within your TR. Doing this
often and randomised is what is commonly called event-related fMRI.
Volkmar
On Fri, 18 Aug 2006, Susana Novais Santos wrote:
> Dear Volkmar,
>
> Thanks so much for your quick reply. I am disappointed to learn there is no
> way to obtain the activation curve for a voxel for a given TR.
>
> Our problem is as follows: In our study, we observe several regions activating
> during a certain TR (3 seconds). We are trying to understand the sequence in
> which those regions activate (which region peaks first and so on), in order to
> establish a functional connectivity model with some temporal information. Do
> you have any other suggestions?
>
> Thanks very much,
> Susana
>
>
> On Aug 17, 2006, at 3:01 AM, Volkmar Glauche wrote:
>
> > Dear Susana,
> >
> > if I understand you correctly, there is no way to get a "temporal series
> > of activation values" with a time resolution higher than TR. Also, the
> > single value you got is not the "peak activation for that time period",
> > either.
> > In a fMRI experiment one usually observe each voxel in a 3D data set
> > exactly once per TR. Thus, you sample BOLD response in each voxel at a
> > sampling frequency of 1/TR. One may get a higher time resolution per
> > event type if you either shorten your TR (acquire less slices, smaller
> > FOV...) or in an event-related design where one usually acquires many
> > instances of BOLD responses for the same stimulus and the stimulus onset
> > SO is somehow randomised with respect to TR. By re-ordering your
> > timepoints in terms of SO, you get a peri-stimulus time histogram with a
> > higher time resolution than TR.
> >
> > Volkmar
> >
> > On Thu, 17 Aug 2006, Susana Santos wrote:
> >
> > > Dear All,
> > >
> > > I am trying to obtain the activation at a given voxel during a whole
> > > TR (3 seconds). I know how to
> > > extract the single value that represents the peak activation for that
> > > time period, but how can I obtain
> > > the temporal series of activation values for the whole duration of
> > > the TR?
> > >
> > > Thanks very much in advance for your help,
> > > Susana
> > >
> > >
> >
> > --
> > 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
>
>
>
--
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
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