# Slow dwiconvert on HCP data

**URL:** <https://community.mrtrix.org/t/slow-dwiconvert-on-hcp-data/8803>\
**Category:** Uncategorized\
**Created:** [August 2, 2026, 10:32am UTC](https://community.mrtrix.org/t/slow-dwiconvert-on-hcp-data/8803 "2026-08-02T10:32:23Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![antoniodm](https://community.mrtrix.org/letter_avatar_proxy/v4/letter/a/a87d85/32.png) [@antoniodm](https://community.mrtrix.org/u/antoniodm)\
**Post date:** [August 2, 2026, 10:32am UTC](https://community.mrtrix.org/t/slow-dwiconvert-on-hcp-data/8803/1 "2026-08-02T10:32:23Z")

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Hello!

I’ve been using MRtrix for a while. Lately I’ve noticed that commands like dwi2response and dwi2fod spend an unexpectedly long time just getting the data into memory. Watching the process, nearly all the wall-clock time goes to this step:

`mrconvert Diffusion/data.nii.gz -fslgrad Diffusion/bvecs Diffusion/bvals diffusion.mif -force -strides 0,0,0,1`

My understanding is that the -strides 0,0,0,1 reorders the data so the volume axis is contiguous, making downstream per-voxel access faster. My data is HCP (~145 volumes, 1.25 mm iso, gzipped NIfTI), with data on local storage.

Is this conversion something I can skip or speed up? Ideally I’d like to avoid paying this cost repeatedly across many subjects. Thanks!