I believe both binaries will use the grad_dev to perform the correct described 
in the bvals and bvecs in a voxelwise manner.

Peace,

Matt.

From: 
<[email protected]<mailto:[email protected]>>
 on behalf of Athanasia Metoki 
<[email protected]<mailto:[email protected]>>
Date: Monday, October 9, 2017 at 3:29 PM
To: "[email protected]<mailto:[email protected]>" 
<[email protected]<mailto:[email protected]>>
Subject: [HCP-Users] dtifit, bedpostx, voxel-wise correction of dMRI gradients

Dear HCP experts,

I would like to analyze some HCP diffusion data. I am using the preprocessed 
HCP data from the 900 subjects release.

I would like to do dtifit and run bedpostx and then tractography (I know dtifit 
is unrelated to the latter bt I'm mentioning it because I would like to be 
consistent in my analysis).

Two questions:

a) I found this dtifit command in the HCP mail list archives:

dtifit -k data.nii.gz -r bvecs -b bvals -m nodif_brain_mask.nii.gz -o >>> 
$OUTDIR/$SUBJECT/dti --gradnonlin=grad_dev.nii.gz

But also I found this code for voxel-wise correction of dMRI gradients:
https://www.humanconnectome.org/storage/app/media/documentation/data_release/Q1_Release_Appendix_II.pdf

When I run the dtifit command above do I use the new_bvals and new_bvecs?

Hence do I run:
dtifit -k data.nii.gz -r new_bvecs -b new_bvals -m nodif_brain_mask.nii.gz -o 
>>> $OUTDIR/$SUBJECT/dti --gradnonlin=grad_dev.nii.gz

or does the "--gradnonlin=grad_dev.nii.gz" in the command does the same job as 
the code I found in the Q1_Release_Appendix_II.pdf?

b) When I run bedpostx_gpu do I need to use the new_bvals in a script like this:
bedpostx_gpu T1w/Diffusion -n 3 -b 3000 -model 3 -g —rician

Thank you.

Best,
Athanasia Metoki
Psychology Doctoral Student - Brain and Cognitive Sciences Program
Cognitive Neuroscience Laboratory
Temple University
Department of Psychology
1701 N 13th St.
Philadelphia, PA 19122
Email: [email protected]<mailto:[email protected]>

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