Hi - you probably want to use SIENA for this comparison; it uses FLIRT
(etc) in a way particularly tuned to fined longitudinal change.
No - FLIRT applies affine registration, so cannot give a "different"
result for the ventricles as for the rest of the brain.
FAST attempts to remove bias field, so if it is working optimally then the
two cases should give similar results. Case (ii) is similar to doubling
the number of iterations of the main FAST loop, i.e. won't change things
if the original number of iterations was sufficient.
Cheers.
On Wed, 30 Jun 2004, Himachandra Chebrolu wrote:
> Hello FSL'ers
> I've two questions.One regarding FLIRT and the other regarding FAST.
>
> 1. FLIRT : In the longitudinal study we are performing, when we have
> registered brains of the same subjects scanned at two different points
> in time we observed a difference in the ventricles. So we looked at the
> histograms and tried to come up with a rationale hypothesis to why this
> was happening,but we could'nt find any. So I was wondering if using
> FLIRT might have introduced some error in the ventricles area. Can
> someone give me any ideas on creating a weighting volume?
>
> 2. FAST : Is the FAST affected by RF bias
> i.e. does it behave the same when (i) The output from the BET is given
> as input (ii) when the restored volume(bias removed) is given as input.
>
> Thanks,
> Himachandra
>
>
>
>
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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