Dear Amit, Marko, List,
I also have a (probably naive) question regarding the SNR measures described
by Peter Kingsley in his email (just re-read it) as well. When I understand
his post well, this classical type of SNR is for noise over voxels within a
single MR image. This might be interesting for anatomical images. For fMRI
though, I'd say it is much more interesting to now something about
singal-noise relation ships in time instead of in space, i.e. random
variations in time with respect to mean signal in time, or even better,
task-rest related amplitudes with respect to noise. To get a first idea on
SNR i sometimes simply divide mean signal (over time!) of a voxel or of the
average time signal of bunch of voxels in an ROI, and divide it through the
SD (over time!). One can then make an SNR image when doing this for each
voxel in a time series. For functional imaging that is much more informative
i'd say. There definitely are better measures for detectability of a signal
based on SNR measures at rest, I would also be interested in hearing about
them (and I'll dive deep into Medline of course). Perhaps we could explore
posters on fMRI-SNR measures next week in Toronto at the HBM together ;-)
Thanks for all your responses,
Bas
> Op donderdag 9 juni 2005 08:40, schreef Marko Wilke:
> > Hi Amit,
> >
> > > How can I calculate the signal to noise ratio in an fMRI data set? (ie
> > > make an SNR map) Is SNR contrast related (ie a different SNR for each
> > > contrast), or is it independent of the task (in which case I can just
> > > use a time series from a baseline rest condition)?
> > >
> > > Finally, what SNR levels are considered "good"?
> >
> > there was a very nice and very thorough mail on that from Peter Kingsley
> > on March, 24th, 2005, on this issue. I think most of your questions will
> > be answered there.
> > Best,
> > Marko
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