Dear Joaquim and SDM users,

While undertaking a coordinate meta-analysis (VBM gray matter - but potentially could apply to fMRI) I came across a unusual ring/circle rather than a blob on the final SDM map. I am unsure if this is an unusual error/artifact or there is some other reason for this. Please see attached image

I have simplified the SDM analysis to see if others can reproduce this - the blob is from a single coordinate at 22,-51,-48 with a t score of -4. Looking at the attached image on the left is the image MyMean_z_p_0.00500_1.000_10_neg.nii.gz on the right is the image pp_StudyA.nii.gz. The right image shows the preprocessed image of the single coordinate - one can see the gray matter mask affects the region but does not touch the maximum, however in the thresholded negative z score image (left) the effect is quite different and there is a ring around a z score of zero

To simplify the analysis I have only 3 studies and 2 of these have no coordinates and one study has the single coord - even if other studies are added the aftifact remains.
I will attempt to attach the input files in a follow-up email.

I am using SDM 4.31 on linux (virtual machine on a Mac) but one of my students reproduced this on SDM 4.31 on Windows

Many thanks,

Matthew