Dear Diederick,

were all subjects acquired at point 1 with 1.5T and at point 2 with 3T? Or was the same subject acquired with the same scanner at both timepoints? In the first case, could it be simply a problem of scanner-related variability of ICV assessment (different scanner – different sequence parameters – different performance in assessing ICV)?

Regards,

Paola Valsasina

Da: freesurfer-bounces@nmr.mgh.harvard.edu [mailto:freesurfer-bounces@nmr.mgh.harvard.edu] Per conto di Diederick Stoffers
Inviato: lunedì 20 dicembre 2010 12.49
A: Freesurfer List
Oggetto: [Freesurfer] ICV differs systematically in repeated measurements

Hi all,

I have a dataset with AD patients that were scanned twice, once at 1.5T and once at 3T at an interval of a few years. The ICV values are lower for almost all subjects at timepoint two (FS 5.0). Isn't ICV in the later FS versions supposed to be independent of brain volume as it is based on a scaling factor derived from the Tailairach transform of the skull? Many thanks!

Cheers,

Diederick