Hi salil, the command for that are on the wiki. You'd do a one sample group mean (-osgm) . This asks if the variable of interest is significantly different from zero. Since you ran long mris slopes, that variable would be for example the rate of change or the percent change (one measure per subject). Best Martin

Sent via my smartphone, please excuse brevity.

-------- Original message -------- From: Salil Soman salsoman@stanford.edu Date:07/01/2014 9:40 PM (GMT+01:00) To: free surfer freesurfer@nmr.mgh.harvard.edu Subject: [Freesurfer] longitudinal QDEC question

Hi,

I have been following the steps for longitudinal processing from here (https://surfer.nmr.mgh.harvard.edu/fswiki/LongitudinalTwoStageModel), and was hoping for some advice on how to setup the GLM.

I have a set of data where I have 2 time points for all subjects, have run recon-all, qcache, the base and cross steps of processing. I also ran the long mri_slopes step, created my long.qdec table, then created the simplified table for qdec.

I would like to perform a whole brain analysis where I identify any brain regions that changed (volume or cortical thickness) from time point 1 and time point 2. I am a little unclear on what the explanatory variable should be performing this analysis. Any suggestions on how best to structure the analysis would be greatly appreciated.

Best wishes,

Salil Soman, MD, MS