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Question Posted 10/09/19:
I'm trying to draw FA and MD from the imaging data, so I need bval, and bvec files. When I tried to get them by converting DICOM files to nifty files using dcm2niix software, only generated files are .Jason and .nifty, not bval and bvec. How can I get them? Is it same for every images as long as they used same machine? (For example, it seems that most of imaging data I'm using is from SIEMENS. )
Response posted 10/10/19 by Rob Reid:
It sounds like you are using DICOM files which are already FA and MD instead of the original "raw" diffusion MRI data. If you are getting the ADNI processed FA and MD images then you do not need bval and bvec files to get FA and MD, because you already have them.

If you start with the original 4D diffusion MRI DICOM, dcm2niix will produce a .json, a .bval, a .bvec, and at least one 4D .nii.You would then have to apply a diffusion processing pipeline to the 4D .nii to get 3D FA and MD images. Or you could simply discard the 4D .nii and use the ADNI-processed 3D FA and MD images, keeping the .bval, .bvec, and .json files as metadata.
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