Dear Susan,
there are still quite a lot of possible causes: your total acquisition
time has become shorter, so there must be some differences in MRI
parameters. Also, temporal autocorrelation will be estimated in a
different way, since your TR has become longer than before. I would
suggest to take a look at some time series in your "cluster" dataset in a
region where you saw differences in the original experiment (you may use
SPM volumes toolbox - see the SPM extensions web page - to extract the
data).
Volkmar
On Mon, 24 Sep 2007, Susan Shuai wrote:
>
> Dear Volkmar,
>
> My experiment is still a block design. Actually I have tried the methods
> both with and without slice timing. And the parameter setting is exactly
> what you suggested below. But the result is quite different from the
> original 2sec TR (continuous acquisition) analyzed result. For the
> original one, I got significant differences in contrasts I want.
> However, for the second experiment (cluster acquisition), both analysis
> methods did not show differences.
>
> I am not sure whether it is because of the individual differences,
> hemodynamic changes caused by introducing TD or wrong analyzing
> procedure. I followed SPM manual, the first two examples' procedure in
> chapter "data sets" to do the analysis with my own parameters.
>
> Should I send you a more detailed SPMPrint file?
>
> Thank you and Best regards,
> Susan> Date: Mon, 24 Sep 2007 10:56:42 +0200> From: [log in to unmask]> Subject: Re: [SPM] Feel desperate in analyzing the discontinuous acquisition data> To: [log in to unmask]> > Dear Susan,> > your setup with silence periods between each scan is indeed tricky. If > your experiment can be modelled as a block design, I would go for> - no slice timing correction> - model TR as 3000 ms> - model blocks with onsets and duration> > If you really need to model the design event-related, then you should > enter TA as 1.55 secs and TR as 3.0 secs. For modelling, your TR would be > 3 seconds, and you have to set your reference time bin in a way that it > corresponds to the time when your reference slice was taken.> > hope this helps,> > Volkmar> > On Fri, 21 Sep 2007, Susan L. SHUAI wrote:> > > Dear SPMers,> >> > I am just a new comer to use SPM and doing fMRI experiment. I have> > encountered much difficulty in analyzing the data now. My experiment> > design is a
!
> block design and the acquisition is a cluster acquisition> > because it will allow for silence to present auditory stimulus.> >> > Should I follow the Event-related analysis? In slice timing, what should I> > put as TA? Is it the start time of the last slice acquisition? For> > example, I have 32 slices, and they are acquired in 1.6s. Is the TA 1.55?> >> > In the original experiment, I did the continuous acquisition and the TR is> > 2000ms. In the cluster acquisition, the TR is 3000ms and TD is 1400ms> > allowing for silence. But the analyzed results are very different. In the> > first case, most contrasts show significant differences, while in the> > second case, little contrasts show differences.> >> > I think the slice order and reference slice are all set right. What would> > be the reason for such large differences? How can I check my analyze> > result? I am feeling desperate about the situation now.> >> > Thank you for your help!!> >> > Regards,> > Susan> >> > -- > Vo
!
> lkmar Glauche> -> Department of Neurology volkmar.glauche@uniklinik-fr
> eiburg.de> 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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--
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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