Hi - if you are using the *_seg hard segmentation output from FAST, then
yes the voxel count should add up exactly - I just tested it on the FEEDS
data here and it does add up. If you are getting different results then
feel free to upload a compressed tarfile to
http://www.fmrib.ox.ac.uk/cgi-bin/upload.cgi
and email me the upload ID.
Cheers, Steve.
On Thu, 28 Jul 2005, Heather Emmerton wrote:
> Quick question (forgive me if it has already been answered somewhere in the archives)...
> I've been running T1 weighted structural images through BET, followed by FAST to
> skull strip and g/w/csf segment these images. If I ask avwstats for the nonzero
> volume of the image (avwstats image_brain -V), the output volume is SLIGHTLY larger
> than if I perform a segmentation using FAST and add up the individual tissue volumes
> from the 3 tissue class images. The difference is less than 5 percent, but my
> understanding is that FAST is a hard segmention, so should they not exactly match?
> eg Whole volume output:
> 1115645 voxels
> Grey 539585 voxels
> White: 416314 voxels
> CSF: 141713 voxels
> = 1097612 voxels
>
> 1097612/1115645 = 0.9838...
>
> Your thoughts on where this lost volume is disappearing to would be much appreciated.
> Thanks!!
> Heather
>
--
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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