Hi Caroline
I would recommend the cut-off to be determined by the stability of
your scanner. Only if it is very stable you can justify longer
periods for the filter e.g. 288s but I doubt it :-( One way to test
if your filter works is by obtaining a time-course of a phantom and
use SPMd to test what cut-off period is required to remove hardware
drifts in your setting.
Best
Torben
Torben E. Lund
Danish Research Centre for MR
Copenhagen University Hospital
Kettegaard Allé 30
2650 Hvidovre
Denmark
email: [log in to unmask]
webpage: http://www.drcmr.dk
On 2 Dec 2006, at 08:20, Mohr, Christian wrote:
> Hello Caroline!
> I am very interestet in this topic... And the answers you will get
> from the list
> In my opinion SOA (stimulus onset asychrony) describes the relation
> of TR to aquired volume and condition:
> For event-related designs, you avoid the stimulus onset occuring
> every time in the same slice you aquire. So you vary the SOA until
> every stimulus occure in a different slice of your volumes, e.g.:
> (Design) event = duration 2 sec, TR = 2.5 sec
> stimulation sequence: 3 x TR baseline, event, 4.2 x baseline, event
> 3.8 x TR, event, 4 x TR ...
> So you get data of the early BOLD-responses in different slices and
> fMRI-data will be improved.
>
> The high-pass-filter for block-design should not collide with your
> activity-blocks as you mentioned. If you chose HPF = 144 sec, I do
> not think it will affect your data, but I am not sure!!!
> When you chose HPF = 36 sec, it will eliminate data of interest.
> In my exeperimnets (block-designs: stimulus 10.5 (6) sec, baseline
> 21 (18) sec) I chose HPF = 128 sec (I think the default).
>
> Hope you get more help from real experts!
>
> Best,
> Chris
>
>
> Caroline Tam schrieb:
> > Dear List,
> >
> > I am having a block design with 4 conditions and each condition
> lasts 36s.
> > So the total SOA is 4x36s = 144s.
> >
> > What is the correct HPF cutoff frequency then?
> > Should it be still 2x the SOA?
> >
> > best
> > caroline
>
>
> Christian Mohr
> Klinik für Neurologie
>
> Universitätsklinikum Schleswig-Holstein
> Campus Lübeck
> Ratzeburger Allee 160
> 23538 Lübeck
>
> Telefon: +49 451-500-3709
> FAX: + 49 451-500-2489
> email1: [log in to unmask]
> email2: [log in to unmask]
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