[Freesurfer] mri_label2vol - Questions about label file and missing voxels?

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Hello freesurfer experts,

I am using mri_label2vol to convert my surface drawn label (of functional activity) to functional space (nifti) for more analysis (prf).

When I open the label file in text editor - it shows two lines at the top #!ascii label , from subject vox2ras=TkReg 1287

1) Does the number 1287 represent selected voxels or does it represent something else?

I use the following command to convert:

mri_label2vol --subject sub-01 --hemi lh --label CustomLabel/lh.V1.label --regheader /sub-01/mri/orig.mgz --temp /sub-01/ses-1/mri_files/func_ref_file.nii.gz --o /prfdata/prfroi_mask/lh.V1.nii --fillthresh .3 --proj frac 0 1 .1

2) When I load the nifti file in python, I do not get 1287 voxels, I get only ~300 voxels. Why do I get so few voxels ?

Any help is appreciated.

Cheers,

Dev