Hi Anthony, I don't think so. The problem is that the fundamental T1 contrast is different at 3T than att 1.5T, which results in systematic biases.
cheers Bruce On Mon, 20 Dec 2010, Anthony Dick wrote: > 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. >> > > > _______________________________________________ Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer
