Hi Salil, please send questions to the free surfer mailing list.
If you used the longitudinal stream for processing the etiv should be the same in all time points. It is computed in the 'base' = within subject template once for the entire series. It seems that you did not run your images through the longitudinal stream if your etiv is different across time points. For longitudinal processing see here: http://freesurfer.net/fswiki/LongitudinalProcessing Bes,t Martin On Nov 10, 2013, at 3:37 PM, Salil Soman <salso...@stanford.edu> wrote: > Dear Dr. Reuter, > > I have performed freesurfer 5.3 with hippo subfields Analysis on patients > that have 2 consecutive scans (pre and post surgery). I have generated > Segstats statistics for each individual time point. I have noticed the etiv > is different on all of the cases for each time point (scan 1 is different > from 2). This has led me to worry that it may not be legitimate to perform > analyses of changes in volumes of structures by computing differences in > values between time points). I am writing to inquire if you were familiar > with /had an opinion regarding this matter. > > Best wishes, > > Salil Soman, MD, MS > Postdoctoral Research Fellow - Stanford Radiological Sciences Laboratory > Fellow - Palo Alto War Related Illness and Injury Study Center > WOC Neuroradiology Attending - Veterans Affairs Palo Alto Health Care System > --------------------------------- Dr. Martin Reuter Assistant in Neuroscience - Massachusetts General Hospital Instructor in Neurology - Harvard Medical School MGH / HMS / MIT A.A.Martinos Center for Biomedical Imaging 149 Thirteenth Street, Suite 2301 Charlestown, MA 02129 Phone: +1-617-724-5652 Email: mreu...@nmr.mgh.harvard.edu reu...@mit.edu Web : http://reuter.mit.edu
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