Hi Bjorn,
No there is no simple SNR setting since we found that it was not
straightforward
to come up with a definition that would work for all cases. What you
can do is
estimate the signal level in your noise-free image using fslstats (a
high percentile
might work well) and then calculate the appropriate sigma value for
the SNR that
you want. I cannot tell you a "normal" sigma value because it depends
massively
on the pulse sequence parameters and what the image intensities end up
being.
Try calculating things using fslstats.
All the best,
Mark
On 18 Apr 2008, at 10:16, Bjorn Roelstraete wrote:
> I mean in possum
>
> Steve Smith wrote:
>> Do you mean in POSSUM or (e.g.) with fslmaths?
>> fslmaths currently doesn't have an option to add noise - though it
>> will in the next release.
>> Cheers.
>> On 18 Apr 2008, at 09:51, Bjorn Roelstraete wrote:
>>> Dear all,
>>>
>>> It appears that i cannot add noise in terms of SNR with the
>>> command line. There is only a sigma value to be specified. Is
>>> there a good sigma approximation of say a 10% SNR? If not, what
>>> would be "normal" sigma values to use? Thank you.
>>>
>>>
>>> Kind regards,
>>> --
>>> Bjorn Roelstraete
>>> Ghent University
>>> Department of Data-analysis
>>> H. Dunantlaan 1, B-9000 Gent, Belgium
>>> Tel: 32-9-2646434
>>> E-mail: [log in to unmask]
>>>
>> ---------------------------------------------------------------------------
>> 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
>> ---------------------------------------------------------------------------
>
> --
> Bjorn Roelstraete
> Ghent University
> Department of Data-analysis
> H. Dunantlaan 1, B-9000 Gent, Belgium
> Tel: 32-9-2646434
> E-mail: [log in to unmask]
>
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