This is just a thought, but is this issue mitigated to some degree if you can show that the regions in which you are interested meet a certain minimum signal to noise ratio? Or maybe a more stringent requirement would be necessary, such that the SNR of the ROIs don't differ significantly?
Always wondered about this. Anthony On 12/20/10 9:26 AM, Martin Reuter wrote: > 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.stoff...@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 > _______________________________________________ > Freesurfer mailing list > Freesurfer@nmr.mgh.harvard.edu > https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer > > > The information in this e-mail is intended only for the person to whom it is > addressed. If you believe this e-mail was sent to you in error and the e-mail > contains patient information, please contact the Partners Compliance HelpLine > at > http://www.partners.org/complianceline . If the e-mail was sent to you in > error > but does not contain patient information, please contact the sender and > properly > dispose of the e-mail. > -- Anthony Steven Dick, Ph.D. Assistant Professor Department of Psychology Florida International University Modesto A. Maidique Campus DM 296B 11200 S.W. 8th Street Miami, FL 33199 Phone: 305-348-4202 Lab Phone: 305-348-9057 or 305-348-9055 Fax: 305-348-3879 Email: ad...@fiu.edu Webpage: http://www.fiu.edu/~adick _______________________________________________ Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer
