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Question Posted 11/17/20:
Hi ADNI team,

I am interested in using quality controlled DTI images (Preprocessed) and I could successfully download the images. Could you tell me how I can query the b-table for those preprocessed images? I believe that I cannot use the raw dcm's b-vectors because the b-vectors need to be corrected based on the image transformation. Thank you.

Best regards,
Response posted 11/18/20 by Rob Reid:
The best way to get the b table is with a dicom to NIfTI converter such as dcm2niix. No additional transformation should be needed at that point. If you use FSL's eddy to correct for head motion it will also output a rotated bvec file that accounts for the head motion, but the difference is small.

If you change the image coordinate system, e.g. LPS to RAS, you may have to flip a component of the b vectors (most likely x) before doing tractography, but that will not affect FA or MD.
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