Hey guys,
I am working with Freesurfer 7.1.1. to compare two groups' cortical thickness values within Desikan-Killiany ROIs while correcting for (mean-centered) sex. I have extracted thickness values within ROIs into a txt using aparcstats2table and have then used mri_glmfit --table Study.txt to perform group analysis on thickness values within ROIs.

For a future analysis, I want to extract the t-statistic (corrected for sex) per ROI into a txt/csv. This post (MailScanner has detected a possible fraud attempt from "secure-web.cisco.com" claiming to be https://www.mail-archive.com/freesurfer@nmr.mgh.harvard.edu/msg06048.html) states that F.mgh stores the F-ratio, which is F=t^2, so t=sqrt(F). So, in principle, I should be able to calculate t from my F.mgh file. However, using the squareroot will only yield positive values. I have run a t-test on my data (using simply Python scipy.stats.ttest_ind): the values are actually the same as using sqrt(F), but signs differ (since t calculated from F can only be positive).

Is there a better way to calculate a t-statistic while regressing out a covariate within ROIs?
Many thanks in advance, Melissa