Hi,
There is no pre-defined minimum size threshold. It depends on
the voxel size, the z-threshold and the measured smoothness
from the data. Are you confusing this with the connectivity which
is always 26? (that is, voxels are considered connected if they are
in the 26-voxel neighbourhood of each other - that is, all neighbours
within a 3x3x3 neighbourhood)
The thresholding is actually done using the specified p-value
which is a function of the z-threshold, measured smoothness,
and number of voxels in the cluster. The exact formula is
quite complicated. If you want, you can find more information at:
http://imaging.mrc-cbu.cam.ac.uk/imaging/PrinciplesRandomFields
All the best,
Mark
On 1 Dec 2009, at 19:42, Carlos Faraco wrote:
> I have some results results that were cluster thresholded in Feat
> using the
> default z and p-values, and of course the minimum cluster size of
> 26. The
> results of this analysis are null. I thresholded the z-stat image
> from the
> stat directory in fslview using a z of 2.3. There are clusters of
> contiguous
> voxels that have much more than 26 voxels. What is the reason why
> this is
> happening? Is there anything else that is being done when the cluster
> program thresholds at the specified minimum cluster size?
>
> Thanks,
>
> Carlos Faraco
>
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