Hi everyone,
I came across this discussion as I was browsing a different topic. I just wanted to comment about "concatenating" two separately acquired DTI data with two different b-values. Normally, if you are doing multiple b-value acquisitions, it is preferred that data is acquired in one run. Once you stop and do the next, you have to ensure that TE and TR are identical, RF transmit and receive gains are identical and image reconstruction did not use an arbitrary scaling (essentially all acquisition parameters have to be identical). If any one of those variables is different between the two acquisitions, their attenuations will be modulated by b-values plus any change in acquisition parameters. That will mislead DTI parameter estimations.
--tugan
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