Hi Joy-Loi,
so you have 2 time points? the first with a single scan, the second with two within-session scans that you want to average? I don't understand exactly what you are trying to do. To test differences in reliability you'd have to scan a bunch of subjects twice in a session and then twice in another session. Then you can look at reliability when using only one scan (e.g. the first) or when averaging both scans in both time points. 'varying quality' with respect to motion also scares me a little. There can be individual outliers that severely affect your mean response (unless you have lots of subjects).
Anyway for these things you would process your results through the longitudinal stream (this allows you also to be unbiased with respect to the time point). There are several design questions to consider (e.g. does it make sense to include all virtual time points into the same base, or run everything twice: one base for the averaged images , another for the single images and then compare etc. ) Either way this is not a standard analysis and you'd be pretty much on your own with how to set it up.
Best, Martin
On 03/18/2013 09:02 AM, Joy-Loi Chepkoech wrote:
Hello FreeSurfer experts,
I am currently trying to systematically investigate the differences in cortical and subcortical estimates that occur when performing recon-all on one scan, or when averaging across scans of varying quality with regard to movement.
I have a list of subjects that each have been processed (recon-all) twice (once with one scan and once with two scans), and would like to run some FreeSurfer statistical analysis on them.
Is it feasible to set up a longitudinal analysis similar to the one described here: (http://surfer.nmr.mgh.harvard.edu/fswiki/FsTutorial/LongitudinalTutorial)? If it is, could someone assist me in setting this analysis up? (I have tried following the tutorial, where I on each subject set "0 years" for one scan, and "1 year" for two scans in the QDEC table, but the results from the QDEC analysis don't seem to agree with previous SPSS results that I have).
Thank you,
Joy-Loi _______________________________________________ Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer