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This is not something we have typically done with T1w/T2w myelin mapping. Is there a reason you are especially concerned about these issues? We tend to find that issues with surface placement, which are more prevalent at 1mm isotropic than at higher resolutions, are a far bigger issue and I don’t know that PETsurfer will help with this because it is based on the surfaces themselves. I would recommend just sticking with the default HCP Pipelines approach for T1w/T2w myelin mapping.

Matt.

From: freesurfer-bounces@nmr.mgh.harvard.edu on behalf of Marina Fernández marina.fdez.alvarez@gmail.com Reply-To: Freesurfer support list freesurfer@nmr.mgh.harvard.edu Date: Tuesday, May 24, 2022 at 10:54 AM To: "freesurfer@nmr.mgh.harvard.edu" freesurfer@nmr.mgh.harvard.edu Subject: [Freesurfer] Tissue fraction effects correction

External Email - Use Caution Dear FS experts,

We are planning to correct for tissue fraction effects on T1w/T2w ratio images using PETsurfer, setting the point spread function estimate to zero. My questions are:

1. Does it make sense to correct for tissue fraction effects on T1w/T2w ratio images even when T1w and T2w images were acquired using the same matrix size with identical voxel resolution (i.e., 1mm3)?

2. If that makes sense, which PVC method would work best for correcting tissue fraction effects (i.e., SGTM, MG, RBV) on structural MRI scans?

Many thanks in advance.

Best, Marina

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