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.
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!
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