Hi Diederick,
In a longitudinal study you need to ensure identical acquisition and processing, else you'll introduce a systematic bias. Some of my recent analyses indicate that even updating the software on the scanner can bias your results. Hardware changes are worse.
Best Martin
On Dec 20, 2010, at 6:48 AM, Diederick Stoffers d.stoffers@gmail.com wrote:
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 _______________________________________________ Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer