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Thanks for getting back on this.

Best - Don

From: freesurfer-bounces@nmr.mgh.harvard.edu freesurfer-bounces@nmr.mgh.harvard.edu On Behalf Of Yendiki, Anastasia Sent: Monday, October 21, 2019 10:25 PM To: 'freesurfer@nmr.mgh.harvard.edu' freesurfer@nmr.mgh.harvard.edu Subject: Re: [Freesurfer] tracula FA question - 2 cohorts/2 scanners

Hi Don - Diffusivity and FA depend on the b-value. Even if you just scan a subject with multiple b-values on a single scanner, and you compute FA etc from each shell, you'll get different values in the same voxel. So this is unrelated to what tractography method you use, tracula or other. There is literature on harmonization of diffusion measures across scanners, you might want to look into that.

a.y ________________________________ From: freesurfer-bounces@nmr.mgh.harvard.edumailto:freesurfer-bounces@nmr.mgh.harvard.edu <freesurfer-bounces@nmr.mgh.harvard.edumailto:freesurfer-bounces@nmr.mgh.harvard.edu> on behalf of Krieger, Donald N. <kriegerd@upmc.edumailto:kriegerd@upmc.edu> Sent: Monday, October 21, 2019 7:37 AM To: 'freesurfer@nmr.mgh.harvard.edu' <freesurfer@nmr.mgh.harvard.edumailto:freesurfer@nmr.mgh.harvard.edu> Subject: [Freesurfer] tracula FA question - 2 cohorts/2 scanners

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I have tracula runs on two cohorts whose imaging was obtained on different scanners with slightly different beta's and other parameters.

Would the differences in the scanners and scanning parameters be expected to produce large cohort-wide differences in the FA's?

Can you point to a reference?

Thanks - Don