[Eeglablist] importing fMRI tr events

[Johan]

I'm currently struggling with this one as well.

An added little problem, is the 3T scanner needs a little bit of 'dead time'
just before beginning with a new volume scan. That is, if the TR of the EPI
is set to 'shortest possible' on the scanner. Then you'd have to optimize
for the amount of dead time just before a volume, and then place your
triggers.

Once the triggers are 'somewhat correctly' placed in this way (taking into
account a little bit of 'dead time' just before a new volume, the
oversampling (stage 1) in the fmrib (with matlab's interp function) together
with slice alignment should take care of mis-placement of slicetriggers... i
think.

But... i'm not overly confident if this is indeed the case!


Regards,
Johan








On Jun 15, 2007 8:52 PM, Stefan Debener <s.debener at uke.uni-hamburg.de>
wrote:

> Hi Jenni,
>
>  you need to add event labels and latencies to the EEG.event field, eg,:
>
> evts = length(EEG.event);
> EEG.event(evts+1).latency = 1234567;
> EEG.event(evts+1).type = 'tr';
> EEG = eeg_checkset(EEG);
>
> You should also run eeg_checkset, which will place the new events at the
> correct index in the event field (among other things)...
>
> However, the problem in your case is that the placement of the TR
> triggers should be as accuarte as possible. It is therefore better to
> collect the trigger by reading the TTL from the scanner while recording
> the EEG data with a high sampling rate). Even at 5 kHz sampling, a
> trigger misplaced by just one sampling point will cause problems.
>
> Best,
> Stefan
>
>
>
> Jennifer Wilson wrote:
>
> > Hi,
> >       I'm hoping that this is an appropriate question for the list...
> > We are trying to use the FASTR function on the fMRIB plugin to remove
> > gradient artifacts from ECG data collected from subjects in a 3T
> > scanner.  I can't think of any log files that would have the timing
> > info, so I think I need to make a .txt myself (from scratch) to
> > specify the timing of each slice.  How does eeglab want this
> > information formatted though?   I couldn't find this info on the
> > tutorials online.  Or has anyone found a different method that works
> > well?
> > Thanks!
> >
> > Jenni Wilson
> > Cognitive Neuroscience Lab
> > Department of Psychology
> > Emory University
> >
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-- 
Johan van der Meer
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1056 RN A'dam
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