[Freesurfer] Gray to White Matter Signal Ratio (GWR)

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Dear FreeSurfer team,

I am currently using to Gray to White Matter Signal Ratio (GWR) to analyze our longitudinal AD/MCI MRI data. I feel a little confused about the interpretation after reading some recent papers like Putcha et al, 2022 or Jefferson et al, 2015 and some early papers like Salat et al, 2011 and I hope Freesurfer team could help me confirm if my understanding is correct.

1, Freesurfer "recon-all" generates the GWR map by default using "pctsurfcon" and the T1 image. The formula is 100*(W-G) GWR = --------- 0.5*(W+G)

The white matter is sampled 1mm below the white surface. The gray matter is sampled 30% the thickness into the cortex.

2, Gray to White Matter Signal Ratio (GWR) generated by "recon-all" is the same as Gray and White Matter tissue contrast. So Gray to white matter signal intensity ratio (GWR) declines across the lifespan? AD patients have smaller GWR than cognitively normal elders? Decrease of GWR is observed with increasing AD disease severity?

Thank you so much and best regards,

Xiao Da Senior Data Scientist Cognito Therapeutics, Inc. 1218 Massachusetts Ave, Cambridge, MA 02138 xda@cognitotx.commailto:xda@cognitotx.com [A picture containing text, sign Description automatically generated]