Hi Sebastian,

the etiv is estimated in the base/subject-template, so it is constant for all time points. And if you want to include it into a longitudinal design depends on what you want. If you look at percent changes , you don't have to, but if you look at yearly rates, it is probably a good idea.

Best, Martin

Am 18.02.2017 um 13:52 schrieb Sebastian Huhn:

Dear Freesurfer community,

I wondered, how you correct the longitudinal hippocampus segmentation for total intracranial volume. Our cross-sectional analysis is corrected for total intracranial volume as described, for example, in Kerti et al. 2013 Neurology ( http://dx.doi.org/10.1212/01.wnl.0000435561.00234.ee ).

They used this formula: adjusted volume = raw volume - b*(ICV - mean ICV). The coefficient b represents the slope of regression of a region-of-interest volume on ICV.

Now I am curious how to perform such a correction for intracraial volume for our longitudinal data. Do I correct for example the longitudinal hippocampus volume for timepoint 1, for eTIV found in SUBJECT.long.template/stats/aseg.stats, or for eTIV of the template, or anything else? Or are such corrections even neccessary for longitudinal runs?

Thanks a lot for helping me out of my confusion. Best, Sebastian _______________________________________________ Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer