Try
mri_segstats --seg Cluster1_R.nii.gz --id 1 --sum sum.R.dat
That will give you the number of voxels that have a value=1 times the size of the voxel (so the volume). It will not be in MNI space unless the nifti files you sent are in MNI space.

On 12/21/2022 5:42 PM, Beatriz Cavendish wrote:

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Hello,

I would like to know the step by step to obtain volume (mm3) from a volumetric mask in the MNI space (follow the attached nifti file). I checked the forum but the tutorials are for surface extraction and cortical thickness.

Yours sincerely,

--

Beatriz Araújo Cavendish, MSc

PhD student | Psychologist

University of São Paulo

São Paulo/SP - Brazil

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