[Freesurfer] Difference in GMV generated from qdec and mris_anatomical_stats

Dear FS experts,

I was trying to find the gray matter volume of superior temporal gyrus (STG) for schizophrenia patients using freesurfer. I ran recon-all and generated the rh/lh.aparc.volume.stats using qdec.

From that, I got the volume for left hand lh_superiortemporal_volume,=11893.

Out of curiosity, I separately found the STG volume for this patient alone using the follo. steps. 1. Saved the label lh.STG using tksurfer -annot aparc SZ01 lh pial 2. Then generated the volume using mris_anatomical_stats. 3. I found the value to be 16268.

I'm wondering why there is so much changes in the generation of GM volumes. Can anyone please help me with my query?