Hi Martin,
Thanks for your fast response. Apologies for the second email, I forgot to include the mailinglist.
It makes sense that in the longi-stream results should be more reliable.
However, it worries me if I see segmentation differences up to 500%, for example amygdala volume going from 1475 to 503 Left and 1595 to 281 for Right, independent vs longitudinal stream respectively. In the current study we had a cross-sectional exploration study, followed by a longitudinal validation study (so two different samples). The above worries me if we want to compare the cross-sectional results with the longitudinal results, as the differences between independent and longitudinal are in a linear fashion.
Any thoughts on this?
Cheers, Cédric
From: Martin Reuter <mreuter@nmr.mgh.harvard.edumailto:mreuter@nmr.mgh.harvard.edu> Date: Tuesday, June 25, 2013 8:00 PM To: Cédric Koolschijn <P.C.M.P.Koolschijn@uva.nlmailto:P.C.M.P.Koolschijn@uva.nl> Cc: "freesurfer@nmr.mgh.harvard.edumailto:freesurfer@nmr.mgh.harvard.edu" <freesurfer@nmr.mgh.harvard.edumailto:freesurfer@nmr.mgh.harvard.edu> Subject: Re: [Freesurfer] Differences on baseline volumes within subject cross-sectional vs longitudinal processing
Hi Cedric,
this is as expected, the data changes when using the longitudinal stream (it will become more reliable, removing some of the variance you get in the independent processing). Becuase of the different processing approaches, the results from independent processing (cross) and long will not be directly comparable.
Cheers, Martin
On 06/25/2013 04:02 AM, Koolschijn, Cédric wrote: Hi FreeSurfers,
I ran the longitudinal processing pipeline on my subjects, FS 5.0. Following the tutorial, first independently, then base, then long etc. Everything works well, no problems there.
Out of curiosity I compared the asegstats & aparcstats within subject at baseline (i.e. The same timepoint): so the independent fsid vs the same_fsid.long.same_fsid_template, and there are (large) differences between all volumes/thicknesses. The independent measures are in almost all brain areas larger compared to those derived from the longi-stream. Except for the IC, which is completely the same, but of course, this measure is based on the Buckner method and calculated differently.
Overall this seems a bit strange to me, because I believe there shouldn't be differences within subject on the same time-point. Is this the result of the within-subject template use for the longitudinal data or is something else going wrong, or is this normal?
Many thanks!
Cheers, Cédric
------------------------------------------------------------ P.C.M.P. Koolschijn (Cédric), PhD Dutch Autism & ADHD Research Center Brain and Cognition Amsterdam, The Netherlands E P.C.M.P.Koolschijn@uva.nlmailto:P.C.M.P.Koolschijn@uva.nl W http://www.dutcharc.nl
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-- Martin Reuter, Ph.D. Assistant in Neuroscience - Massachusetts General Hospital Instructor in Neurology - Harvard Medical School MGH / HMS / MIT
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