If the cluster does not exceed your threshold, it is not significant.

However, it seems that you probably didn't constrain
AlphaSim/3dClustSim to grey matter when determining cluster size, but
you are now constraining the voxels you will look at. What I would
suggest is either: (1) don't constrain yourself to only voxels in a
specific region - as the cluster isn't isolated to one region in your
case; (2) constrain AlphaSim/3dClustSim the same way you'd constrain
your interpretation. Then you might get smaller clusters and be able
to report them.

Best Regards, Donald McLaren
=================
D.G. McLaren, Ph.D.
Research Fellow, Department of Neurology, Massachusetts General Hospital and
Harvard Medical School
Postdoctoral Research Fellow, GRECC, Bedford VA
Website: http://www.martinos.org/~mclaren
Office: (773) 406-2464
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On Wed, Oct 10, 2012 at 4:33 PM, Devin Sodums
<[log in to unmask]> wrote:
> Dear SPM users,
>
> I have been analyzing some group data using a Monte carlo simulation (alphaSim), and have a large series of results.  While locating the clusters using xjview, I ran into a question.
>
> If the peak of the cluster is in a grey matter structure, but there aren't enough voxels in that structure to pass the minimum voxel number found when using AlphaSim, do I still report the cluster as significant, and then say that the peak is in this grey level structure, or does that mean that I cannot report this cluster?
>
> For example, this is the output of the cluster selection from xjview:
> From Alphasim, found that need minimum 115 voxels for cluster to be significant, but the grey matter structure with the highest number of voxels is the Angular gyrus (left), and that is only 106 voxels.  Does this mean I can't report the cluster, or do I still report it?
> From what I understand of the Monte carlo simulation analyses, I should be able to, and would actually report the structure where the peak MNI coordinate is exactly, but I wanted to confirm this.
>
> Cluster 1
> Number of voxels: 221
> Peak MNI coordinate: -38 -72  28
> Peak MNI coordinate region:  // Left Cerebrum // Temporal Lobe // Middle Temporal Gyrus // White Matter // undefined // Occipital_Mid_L (aal)
> Peak intensity: 4.1644
> # voxels        structure
>   221   --TOTAL # VOXELS--
>   221   Left Cerebrum
>   208   White Matter
>   143   Parietal Lobe
>   106   Angular_L (aal)
>    79   Supramarginal Gyrus
>    77   Temporal Lobe
>    72   Occipital_Mid_L (aal)
>    64   Middle Temporal Gyrus
>    50   Angular Gyrus
>    15   Inferior Parietal Lobule
>    12   brodmann area 39
>    12   Gray Matter
>    10   SupraMarginal_L (aal)
>     6   Sub-Gyral
>     5   Superior Temporal Gyrus
>     1   Occipital Lobe
>     1   Superior Occipital Gyrus
>     1   Precuneus
>
>
> Thank you for any help,
>
> Devin Sodums