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Question Posted 12/02/13:
I find that during different scan time, the parements are different. TE may vary from 68.3 to 68.6, while TR may fluctuate from 9150 to 13000. I am confused whether those subjects's DTI data can be studied together?
Response posted 12/17/13 by Bret Borowski:
Thank you for your questions to the ADNI MRI Core.

The fluctuations you are seeing are scanner dependent. Even though all DTI scans are collected using General Electric 3T scanners, the performance of the gradients on those scanners differ. For instance the newer GE scanners that are the 750 models with software levels of 20 and higher are able to scan at lower TR's. (In the 9000 range). The older GE scanners with Excite gradients cannot run with the lower TR's, so the scanner needs a higher TR to obtain the same coverage. The TE differences you are seeing are minimal but are also a result of the scanner differences.
We understand that this is an issue, and are still accessing the feasibility of combining the data from the older systems vs. the newer systems.
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