Dear NITRC community,

I am analysing T1 images using CAT12 toolbox to obtain volumetric information about grey matter (Voxel-based morphometry analyses) and cortical thickness. What I have observed doing a simple correlation analysis between participants' relative grey matter volume measures  (normalised for total intracranial volume) and mean cortical thickness is that these two parameters are negatively correlated, which means that participants with higher cortical thickness have less grey matter volume. I know that these two parameters are obtained with different techniques and so they should not be necessarily positively correlated, but a so pronounced negative correlation seems strange as well. 
I have checked the quality of my data and they seem fine (all above B score in the quality check), and grey matter estimation using another software (freesurfer).
Do you think it may be something wrong? How should I interpret this result?

Thank you for your time,

Michele Deantoni