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It really seems like you'd have to add a "simple" covariate based on the scan acquisition--- but in your case it sounds like all of your patients would be in group 1... and all of your controls would be in group2.... so there would be no obvious way to disambiguate the effect of scanner from the effect of patient group. However as you pointed since your basic question is .... are FA changes different between controls and patient population... you've already indicated in your question the answer is yes..... all my patients scanner with higher TR/TEs have higher FA values... I would think it would perhaps depend on the # of patients in your two groups... but perhaps scanning at least 5-10 controls on the "new" scanner might allow you to take into account the effects of scanner in your model... On Wed, Dec 21, 2011 at 7:09 PM, David Brang <[log in to unmask]> wrote: > Hi All > I was wondering whether it's possible to compare FA/MD for DTI acquired > with different TEs (80.4 vs. 86.4) and TRs (13200 vs 15100); all other > acquisition parameters are the same. We have a group of patients acquired > with the latter and a convenient set of control data acquired with the > former, but higher TE/TRs seem to also produce higher FA. Is there any way > to appropriately normalize the datasets or would multivariate statistics > avoid this issue? > Thanks! > David > -- David A Gutman, M.D. Ph.D. Assistant Professor of Biomedical Informatics Senior Research Scientist, Center for Comprehensive Informatics Emory University School of Medicine