[Freesurfer] There is a marked difference between the left and right brain in the reproducibility of volume when 1416 recon-all runs are performed on the same subject

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Dear FreeSurfer team,

We were interested in the reproducibility of multiple runs of recon-all and repeated recon-all 1416 times on the same subject. We then checked the left and right brain results for the volume obtained from the Aseg process. The right brain showed exactly the same volume, while the left brain showed a small variation. We thought that the variation in volume between the left and right brains would be the same. But why is this not the case in reality?

The volume_attemps1416.csv is attached. For example, the Left-Lateral-Ventricle in this file has variation, but the Right-Lateral-Ventricle has no variation, as shown below.

*Left-Lateral-Ventricle*12377.8 12375.9 12375.9 12380 12376.4 ...

*Right-Lateral-Ventricle*7514.7 7514.7 7514.7 7514.7 7514.7 ...

1) FreeSufer vesion: 7.2.0 2) Platform: Red Hat Enterprise Linux 8.6 3) uname -a: Linux fn01sv01 4.18.0-372.36.1.el8_6.x86_64 #1 SMP Thu Nov 17 16:37:07 EST 2022 x86_64 x86_64 x86_64 GNU/Linux 4) volume_attemps1416.csv: Summarized results of 1416 aseg.stats.