Le 10 nov. 2016 à 23:18, Matthieu Vanhoutte <matthieuvanhoutte@gmail.com> a écrit :

Thank you Douglas !

Le 10 nov. 2016 7:21 PM, "Douglas N Greve" <greve@nmr.mgh.harvard.edu> a écrit :

You need to weight by the number of vertices

n = [27805 2321 552];
  m = [8.8194 10.3661 10.3365];
sum(n.*m)/sum(n)

ans =

     8.9637


On 11/10/2016 06:44 AM, Matthieu Vanhoutte wrote:
> Dear Freesurfer's experts,
>
> Could anyone please explain me the difference I got with command line
> in below mail ?
>
> Best regards,
> Matthieu
>
> 2016-08-12 12:07 GMT+02:00 Matthieu Vanhoutte
> <matthieuvanhoutte@gmail.com <mailto:matthieuvanhoutte@gmail.com>>:
>
>     Dear experts,
>
>     I am in trouble with two ways of computing mean intensity with
>     mri_segstats.
>
>     First I have used on .annot files with three different labels
>     inside (SegId 1 to 3) :
>
>     /mri_segstats --annot fsaverage lh cache.th23.pos.sig.ocn.annot
>     --i lh.PET.fsaverage.sm10.mgh --sum lh.pet.sum/
>     /
>     /
>     which give me those results:
>     # ColHeaders  Index SegId NVertices Area_mm2 StructName Mean
>     StdDev Min Max Range
>     1   1     27805    14182.6  cluster-001      8.8194     1.4351
>     6.2105    14.2947     8.0842
>     2   2      2321     1047.3  cluster-002     10.3661     1.0848
>     8.8375    12.9317     4.0942
>     3   3       552      313.1  cluster3      10.3365     0.4711
>     9.3719    11.8694     2.4975
>
>     Second I have created on .label files containing the three
>     segmented labels (SegId 1 to 3) and used this label with mri_segstats:
>
>     /mri_segstats --slabel fsaverage lh
>     lh.th23.cluster.thresh1.3.label --i lh.PET.fsaverage.sm10.mgh
>     --excludeid 0 --sum lh.pet.label.sum /
>     /
>     /
>     which give me those results:/
>     /
>     /# ColHeaders  Index SegId NVertices Area_mm2 StructName Mean
>     StdDev Min Max Range /
>     /  1   1     30678  15542.9  Seg0001 8.9637     1.4701 6.2105
>      14.2947 8.0842 /
>     /
>     /
>     I verified if I obtained the same results with the two ways
>     (.annot or .label) and everything is fine comparing NVertices,
>     Area_mm2 but Mean in first way gives me (8.8194+10.3661+10.3365)/3
>     = 9.84066 and with .label file Mean = 8.9637.
>
>     Did I have miss anything and how is computed mean intensity ?
>
>     Many thanks in advance.
>
>     Best regards,
>     Matthieu
>
>
>
>
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--
Douglas N. Greve, Ph.D.
MGH-NMR Center
greve@nmr.mgh.harvard.edu
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