Question
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,
Heejong
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,
Heejong
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.
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.
