Would this problem also apply for fMRI or diffusion weighted scanning? On 12/20/10 10:41 AM, Bruce Fischl wrote: > 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. >>> >> >> >>
-- 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
