Hi - I'm afraid it's not clear what output image you are talking
about when you say "histogram of the segmented data" - I would not
have thought that histograms of any of the outputs are particularly
meaningful in the sense that you are looking for - the mixture model
is applied to the original data intensities so that's the thing to
look at (or a bias-corrected version of that if you want a 'cleaner'
histogram). If you are looking at partial volume images then yes I
suspect that SPM outputs will be more binariesd-looking than FSL
outputs - but this is not related to the mixture model and original
data histogram.
Cheers, Steve.
On 19 Aug 2009, at 20:55, Mojabi, Pouria wrote:
> Hi all,
>
> I started developing this concern when comparing Segmentation
> results (white matter, grey matter and CSF) between SPM and FSL;
> When looking at for instance Grey matter, as far as the histogram is
> concern, I was expecting to see a Gaussian distribution, is this not
> a correct assumption?
> I could see bell shape histogram for FSL segmented data, but I was
> expecting to see the peak where probability is equal to 1 but the
> peak was at p=0.5
>
> For SPM segmented data, I see a flat histogram with minor peaks at
> p=1 and p=0, not sure why?
>
> I am entirely puzzled by this, based on my understanding of Gaussian
> Mixture Models and Expectation maximization algorithm, you separate
> three Gaussians (ideally speaking, eliminating bias field
> corruption), then you build your probability mask based on the mean
> and standard deviation of the calculated Gaussians, so histogram of
> the Segmented data should somehow reflect this Gaussian nature,
> right ?
>
> Your thoughts on this are highly appreciated
>
> -P
>
>
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Stephen M. Smith, Professor of Biomedical Engineering
Associate Director, Oxford University FMRIB Centre
FMRIB, JR Hospital, Headington, Oxford OX3 9DU, UK
+44 (0) 1865 222726 (fax 222717)
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