Hi - sure, make the isolated voxels of interest have a mean of say
1000 and the background zeros and all should be well.
Cheers, Steve.
On 20 Mar 2006, at 17:20, Lu Yuefeng wrote:
>
>
> Do you have any idea how big mean difference is enough to turn off
> the use of local voxels in the whitening?
> Thanks a lot!
>
> Yuefeng
>
> On 3/20/06, Steve Smith <[log in to unmask]> wrote: Hi - sorry, I
> thought you were talking about the general pre-
> processing steps. To turn off the use of neighbours in the whitening
> just follow my second answer from the last email - cheers.
>
> On 20 Mar 2006, at 15:57, Lu Yuefeng wrote:
>
> > Hi Steve,
> >
> > Thanks for your answers! I have one more question. Could
> > you specify the commands and options to prevent using spatial
> > information to do noise var/cov estimation, since what I really
> > wanted is to simulate a few hundred time series and compare their
> > estimates with other software.
> >
> > Thanks a lot!
> >
> > Yuefeng
> >
> >
> >
> > On 3/20/06, Steve Smith < [log in to unmask]> wrote: Hi,
> >
> > On 19 Mar 2006, at 21:57, Lu Yuefeng wrote:
> >
> > > Hi Steve,
> > >
> > > Thanks a lot for your advice! I got two questions
> > >
> > > (1) I was wondering when I analyze the simulated brain, whether I
> > > could turn off some options to prevent using spatial information
> > > to estimate noise/covariance.
> >
> > Indeed, that's right.
> >
> > > (2) If you would clarify the following question, that would be
> very
> > > helpful for my understanding of SUSAN algorithm. When the same
> time
> > > series were put into a big enough clsuter, would the noise
> variance/
> > > covariance estimates for the time series on the center voxel be
> the
> > > same as those estimates from a single time series, when SUSAN
> > > algorithm is used?
> >
> > If you set the mean intensity of the voxel of interest such that
> it's
> > very different from the mean of its neighbouring voxels, then SUSAN
> > will not include those voxels in the whitening estimation.
> >
> > Good luck - cheers, Steve.
> >
> >
> > >
> > > TIA!
> > >
> > > Yuefeng
> > >
> > >
> > >
> >
>
>
> ----------------------------------------------------------------------
> --
> ---
> Stephen M. Smith, Professor of Biomedical Engineering
> Associate Director, Oxford University FMRIB Centre
>
> FMRIB, JR Hospital, Headington, Oxford OX3 9DU, UK
> +44 (0) 1865 222726 (fax 222717)
> [log in to unmask] http://www.fmrib.ox.ac.uk/~steve
> ----------------------------------------------------------------------
> --
> ---
>
------------------------------------------------------------------------
---
Stephen M. Smith, Professor of Biomedical Engineering
Associate Director, Oxford University FMRIB Centre
FMRIB, JR Hospital, Headington, Oxford OX3 9DU, UK
+44 (0) 1865 222726 (fax 222717)
[log in to unmask] http://www.fmrib.ox.ac.uk/~steve
------------------------------------------------------------------------
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