how to mitigate "WARNING: DTI gradient directions only tested for axial (transverse) acquisitions. Please validate bvec files." about dcm2niix HOT 4 CLOSED

To validate your images, look for the Word document linked at
http://people.cas.sc.edu/rorden/mricron/dcm2nii.html
The issue is that the console/DICOM files report gradients with respect to the scanner coordinates, while NIfTI DTI tools expect the coordinates to be with respect to the image. I have permission from several different groups to share the DICOM DTI datasets from different vendors I used to validate my software:
https://www.nitrc.org/plugins/mwiki/index.php/dcm2nii:MainPage#Diffusion_Tensor_Imaging

I think all the real-world DTI scans I have seen are axial acquisitions:
https://practicalfmri.blogspot.com/2011/11/understanding-fmri-artifacts-good.html

By the way, the version notes for the May 12, 2016 version of Xiangrui Li's terrific Matlab-based dicm2nii suggests he has solved this for GE scanners based on images from Paul (Morgan)
% 160512 get_dti_para: fix bvec sign for GE cor/sag slices (thx paul for data).
I will see if Paul will let me distribute his validation set. If so, should be easy to update dcm2niix for these.

The relevant bits of my code are siemensPhilipsCorrectBvecs and geCorrectBvecs. Xiangrui and I have shared a lot of each others ideas, so these should be pretty similar. The tricks are to work out the patient position (e.g. currently I only allow "head first supine"), image phase encoding (Rows or Columns), Image Orientation Patient, as well as the gradients as reported in scanner coordinates.

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By the way, Paul Morgan provided sample datasets axial/sagittal and coronal images for GE
https://www.nitrc.org/plugins/mwiki/index.php/dcm2nii:MainPage#Diffusion_Tensor_Imaging
these are the same ones Xiangrui used to update his dicm2nii code. If anyone want to modify dcm2niix's geCorrectBvecs function to provide the same output as Xiangrui's get_dti_para for these images I would be happy merge the code into a new release.

If no one offers I will do it when I get some downtime (which may be a while). As I noted, I have not seen these images in the wild, and my software does generate warning messages, so it is not high on my priority list.

I am labeling this issue as an "enhancement", and will keep it open.

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Thank you for all the details -- very much appreciated! Note that many links to zipballs on https://www.nitrc.org/plugins/mwiki/index.php/dcm2nii:MainPage#Diffusion_Tensor_Imaging leading to e.g. http://www.mccauslandcenter.sc.edu/CRNL/sw/dcm2niix/ are 404 now :-/

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I think I fixed all the 404 errors on the NITRC web page. Thanks for the note.

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