probably. The T2* will be different, so you'll have a different TE and different contrast, SNR and CNR On Mon, 20 Dec 2010, Anthony Dick wrote:
> 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. >>>> >>> >>> >>> > > > _______________________________________________ Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer
