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