Dear Evan,
The atlas is designed to be symmetric. Is it possible that the asymmetry is in your data? Another FS user (Chris Vriend, CCed) reported a similar effect (you can find his massage in the archive).
Doug: any further ideas?
Cheers,
/E
Juan Eugenio Iglesias
Senior research fellow
CMIC (UCL), MGH (HMS) and CSAIL (MIT)
From: <freesurfer-bounces@nmr.mgh.harvard.edu> on behalf of "Gallagher, Evan (NGG)" <Evan.Gallagher2@pennmedicine.upenn.edu>
Reply-To: Freesurfer support list <freesurfer@nmr.mgh.harvard.edu>
Date: Wednesday, September 30, 2020 at 14:18
To: "freesurfer@nmr.mgh.harvard.edu" <freesurfer@nmr.mgh.harvard.edu>
Subject: [Freesurfer] Right-side bias in thalamic segmentation pipeline?
External Email - Use Caution
Hi all,
I’ve been working on a project that involves the thalamic segmentation pipeline published by Iglesias et al. in 2018 in NeuroImage (“segmentThalamicNueclei.sh”). While the pipeline itself works great, we have noticed that the right hemisphere
VOIs tend to have slightly larger volumes than the left hemisphere VOIs. This has been true in two separate datasets (n=24 and n=25), neither of which has an obvious physiological trait that would lead us to expect these sorts of hemisphere differences.
This is my first time posting a question on this list, so I’m not sure if images are OK. If yes, there are a couple posted at the bottom of this message that should visualize what I’m talking about. If not, I can say that the volume differences
are most pronounced in the largest VOIs (PuM, VPL, VLp, etc); in these regions, the right side is ~200-300 cmm larger than the left side. Additionally, the average volumes on both sides are reasonable based on Figure 8 of Iglesias et al (in the sense that
our average volumes are well within the violin plots in that figure).
I’m wondering if anyone has encountered this trend before, and/or if there’s a correction I might implement to equalize the volumes. We want to be understand—to the extent possible—the extent to which these differences are driven by biology
vs image processing.
Thanks so much,
Evan
Images follow:
