Rik Henson wrote:
>
> Peter Erhard wrote:
> >
> > Dear Rik, could you please elaborate. See below.
> >
> > On Wed, 9 Feb 2000, Rik Henson wrote:
> >
> > >
> > > > I tried to use slice timing in spm99 for some fMRI data. I expected slice
> > > > timing in spm99b and spm99 to be similar, but they are not! In spm99,
> > > > inputs of TR and TA are required, but NOT in spm99b. The version in
> > > > spm99b is v2.3 and ,in spm99, v2.6.
> > > >
> > > > (An earlier post about TA was found in the archive in Sept 99, but
> > > > generated only one response/follow-up question.)
> > > >
> > > > My questions:
> > > > 1. What is the acquistion time (TA)? Can someone give an example how
> > > > this is determined?
> > >
> > > In simple terms, the TA is the time between acquisition of the first
> > > slice
> > > and acquisition of the last slice of one scan, whereas the TR is the
> > > time
> > > between acquisition of the first slice of one scan and the first slice
> > > of
> > > the next scan (ie TA<=TR). In some acquisition sequences, there is an
> > > appreciable gap between successive scans (TA<TR) which needs to be taken
> > > into account in the slice-timing correction.
> >
> > Is TA not the time between teh start of the first slice and the end of the
> > last slice of one scan. That would make more sense to me ??
>
> You're correct - I'm sorry that I didn't spell it out explicitly, but
> that is what I meant to imply: START of first slice and END of last
> slice.
>
> Rik
I'm sorry, Rik, but your first answer was correct. We used the
timepoints of the fMRI triggers,
measured with an external PC. Therefore I calculated the first parameter
of timing as:
timing(1) = TA / (nslices -1)
and the second one as
timing(2) = TR - TA
This corresponds to the default calculation of TR in the case of batch
processing.
(calling spm_slice_timing with all parameters).
By the way:
the line
eval(['P = P' num2str(subj) ';']);
should be replaced with
if nsubjects > 1, eval(['P = P' num2str(subj) ';']); end;
Sorry again for the confusion
Michael.
>
> ---------------------------8-{)}-------------------------
>
> DR R HENSON EMAIL [log in to unmask]
> Wellcome Department of
> Cognitive Neurology TEL (work1) +44 207 833 7483
> 12 Queen Square TEL (work2) +44 207 833 7472
> London, WC1N 3BG FAX +44 207 813 1420
>
> URL: http://www.psychol.ucl.ac.uk/rik.henson/index.html
>
> ---------------------------------------------------------
--
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
Dr. Michael Erb
Sektion f. experimentelle Kernspinresonanz des ZNS
Abteilung Neuroradiologie
Universitaetsklinikum
Hoppe-Seyler_Str. 3, D-72076 Tuebingen
Tel.: +49(0)7071/2985398 priv. +49(0)7071/61559
Fax.: +49(0)7071/294371
e-mail: <[log in to unmask]>
www: http://www.medizin.uni-tuebingen.de/nrad/sektion
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