Hi,

Usually the bval and bvec info is in the DICOM headers in some way, but the format varies with scanner software and is often buried in private tags. dcm2nii is very good at extracting that info but will fail in two cases.

The most frequent cause is that it fails to recognize the series as a diffusion sequence, because of either missing slices preventing it from making a 4D Nifti, or something exotic about the sequence.

The next most common cause is it not knowing how to get the info for that scanner's software version, but that is fairly rare with recent ADNI scans.

I recommend starting by checking that you have all the slices that were acquired. If that isn't the problem there are other things to try, but they depend on the details of the situation.

dcm2nii prints messages to the terminal about what it *thinks* is going on - those would be a helpful diagnostic.

Hope this helps,
Rob