how are you computing the 20% difference? We definitely don't see this, and Martin has done extensive testing of repeatability. Bruce
On Wed, 27 Jul 2011, Jessica Liu wrote:
Hi Martin,
Thanks for getting back to me. Actually I have two young controls who have 20% differences between two scans a day apart. Visually, there are not abnormalities for the surfaces and hippocampus in both subjects i.e. on tkmedit, the color of the hippocampus area (yellow) looks alright to me. I don't see any motion artifacts either.
Jessica
On Wed, Jul 27, 2011 at 12:15 PM, Martin Reuter mreuter@nmr.mgh.harvard.edu wrote: Hi Jessica,
I don't think this is normal. Is this a single subject? Of course in a single subject lots of stuff can go wrong. Are the surfaces correct? And the hippo label? Are there motion artifacts in the image etc. Anyway, you should process this with the longitudinal stream: http://freesurfer.net/fswiki/LongitudinalProcessing which should increase repeatability. Best, MartinOn Wed, 2011-07-27 at 09:01 -0700, Jessica Liu wrote:
Hi,
We found 20% differences in temporal lobe brain volume and ca. 5% difference in the hippocampus volume between two data sets of a young normal volunteer scanned 2 days apart.
We use the one-step 19 hours recon-all -all procedure and directly sum select values taken from the lh.aparc.stats, rh.aparc.stats, and wmparc.stats. The values summed were based on information given from https://mail.nmr.mgh.harvard.edu/pipermail/freesurfer/2007-April/005000.html
My question is, are these observations normal for Freesurfer? Any comments are greatly appreciated. Thanks! -- Pom & Jessica
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