Hi - it sounds like you maybe have change over time in your imaging. If
there is any change in the hardware/protocol side of longitudinal data
acquisition then SIENAX is not a great way to proceed. SIENA is more
robust to such changes, but doesn't give you separate grey-white analyses.
If your grey-white contrast is poor it maybe doesn't make too much sense
to be attempting to segment them separately anyway. Using priors doesn't
generally help - it just reduces noise but also any estimated changes by
forcing all measurements towards a mean.
Cheers, Steve.
On Tue, 9 Nov 2004, Himachandra Chebrolu wrote:
> Hi FSL'ers
> I've been segmenting high resolution volumes using
> FAST and have observed that the white matter volume
> increased with age!When we went back and looked into
> it it seemed like that there was some
> misclassification going on! Will using the prior
> probabilities for intitialisation help solving this
> problem. One problem with the images is the contrast
> between gray and white matter is not too high!
>
> Thanks,
> Hima
>
Stephen M. Smith DPhil
Associate Director, FMRIB and Analysis Research Coordinator
Oxford University Centre for Functional MRI of the Brain
John Radcliffe 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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