An ROI does not have a GM probabability, so I'm not sure what to say. Perhaps he/she wants the average amount of GM in the ROI relative to the size of the ROI? You can get this with mri_compute_volume_fractions. This will produce maps of the GM fraction in each voxel (separating cortical and subcortical). Just use mri_segstats in the same way you used it for the PET. The output will be the fraction of the ROI that is GM.

On 4/24/2020 8:41 AM, Shane Schofield wrote:

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Hi Freesurfer Team,

I have used mri_segstats to get ythe mean PET uptake across all the parcellations in the WMPARC space. These values were calculated in the native PET space (following the DTI tutorial). A reviewer asked what is the grey matter probability of the ROI and I am not sure how to address this. Any help is kindly appreciated. Thanks.

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