I think your approach of using a covariate will work well enough. The one thing you'll want to check is whether your statistical test will be confounded by headcoil/FSversion. Eg, if all your patients came from 8 channel and all your controls came from 32, then you would not know whether your differences are caused by diagnosis or by head coil.

On 9/10/2025 11:21 AM, Stacey Schaefer wrote:

External Email - Use Caution

Hello Freesurfer gurus,

We have two samples of approximately n~125-150 whose T1s were collected on the same scanner with the same acquisiton, except for a difference in head coil (8 vs 32 channel) and processed with different Freesurfer versions (v5.3.0 and v. 6.0.0). Both also had the FreeSurfer segmentation of hippocampal subfields v 6.0.0 applied. We would like your guidance about combining their data if possible to maximize sample size.

What would your suggestion be for hypothesis testing? Can we combine the samples - for example to test moderators of hippocampal x age relationships, using simply a covariate to account for the differences in acquisition/Freesurfer processing (in addition to the usual sociodemographic and estimated intracranial volume covariates)?

OR is that problematic and would you instead suggest keeping them separate and using one as a replication sample?

Thank you for your guidance!

Stacey

Stacey M. Schaefer, Ph.D.
Leader of the MIDUS Neuroscience Project &

Co-Leader of the MIDUS Admin Core

MIDUS NEURO

Keystone House

901 University Bay Dr

Madison WI 53705
_______________________________________________
Freesurfer mailing list -- freesurfer@nmr.mgh.harvard.edu
To unsubscribe send an email to freesurfer-leave@nmr.mgh.harvard.edu
https://mail.nmr.mgh.harvard.edu/mailman3/lists/freesurfer@nmr.mgh.harvard.edu/