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Hi Johnny, If you used a different TE for the B0-only images, then you have to take into account the T2-weighting in your data. That is, the normal DTI fit: S = S0 e^(-bD) assumes that TE (and TR) is the same for all images. If not, you should replace S0 with S0 e^(-TE/T2), and fit also for T2 (as well as S0 and D). I'm not including any T1 component because if TR is long enough (say, greater than 5 s), as a first approximation all the longitudinal magnetization would have recovered no matter what the exact TR is. Therefore, you could use your data, if you fit them to the right model. I hope this helps, -Pablo On Wed, 18 Feb 2009 09:27:30 +0000, Steve Smith <[log in to unmask]> wrote: >Hi - this would depend on exactly what caused the differences in the >first place, and that is worth looking into. However it is quite >likely the case that the B0 images taken with different acquisition >parameters than the rest of the diffusion dataset are not going to be >safely usable. > >Cheers. > > >On 17 Feb 2009, at 12:54, Johnny Zhuang wrote: > >> Hi all >> >> Recently, we have been collecting and processing our DTI data with 32 >> directions and several separate b0s images (it's recommended that >> every 8 >> directions should have one B0 image). Initially, we want to average >> the >> separate b0s together with the b0 of the 4D DTI data. However, after >> some >> analyses, we found that the grayscale intensity range of the >> separate b0s is >> quite different from that of the b0s acquired together with b1s, >> which maybe >> due to the different scanning parameters (eg. TR and TE). Further, >> it is found >> that the relationship between the intensity range of these two kinds >> of b0s is >> nonlinear, which means that we can not simply average them. Is there >> anyone >> who also came across this sort of problem and knows how to fix it? >> Thanks for your help >> >> Many thanks and regards >> >> Johnny >> >> School of Psychiatry >> University of New South Wales