Hi Christina
You can have a look at Pierpaoli and Basser 1996 (MRM) where Monte
Carlo simulations show the effect of SNR on anisotropy.
The main pattern is that anisotropy is overestimated at low SNRs due
to the sorting bias of the eigenvalues (esp. in grey matter).
You may also want to have a look at Derek Jones' Smashing Peanut
paper, where it is shown that SNR=15 is around the limit where the
effect of overestimating FA becomes a bit less critical (at least for
a bvalue=1000 s/mm2).
Cheers,
Saad.
On 24 Apr 2009, at 17:58, Christiana wrote:
> Hi,
>
> I have been using TBSS and have read your Protocol paper related to
> the acquisition requirements for TBSS. In the paper it is stated
> that an SNR of at least 15 is recommended for the b=0 image. What
> method did you use to estimate this in the b=0 image and were you
> interested in the white matter SNR specifically?
>
> Thanks,
>
> Christiana
>
Saad Jbabdi
Oxford University FMRIB Centre
JR Hospital, Headington, OX3 9DU, UK
+44 (0) 1865 222545 (fax 717)
www.fmrib.ox.ac.uk/~saad
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