[Freesurfer] question about sig.mgh

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Dear freesurfer experts,

I have analyzed intra-group differences in cortical thickness using QDEC. It generated the file sig.mgh. 1.I want to know what does the sig.mgh mean? Which p value and the cluster size this file present? 2.when I clicked the button Monte Carlo simulation (p<0,05) and listed in the qdec output file "mc-z.abs.th20.abs.sig.cluster.summary". However,there is no cluster in the file.Dose that mean there is no significant difference between two groups?

I have attached the contents of the output file and a screenshot of the display window of QDEC.

Thank you in advance for your help.