# DWI Convert: .Nifti to .nrrd gives extremely small file size, unable to run in UKF Tractography

**URL:** <https://discourse.slicer.org/t/dwi-convert-nifti-to-nrrd-gives-extremely-small-file-size-unable-to-run-in-ukf-tractography/8070>\
**Category:** Support\
**Tags:** dwiconvert\
**Created:** [August 17, 2019, 7:26pm UTC](https://discourse.slicer.org/t/dwi-convert-nifti-to-nrrd-gives-extremely-small-file-size-unable-to-run-in-ukf-tractography/8070 "2019-08-17T19:26:47Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![Bex](https://avatars.discourse-cdn.com/v4/letter/b/4bbf92/32.png) [@Bex](https://discourse.slicer.org/u/Bex)\
**Post date:** [August 17, 2019, 7:26pm UTC](https://discourse.slicer.org/t/dwi-convert-nifti-to-nrrd-gives-extremely-small-file-size-unable-to-run-in-ukf-tractography/8070/1 "2019-08-17T19:26:47Z")

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Operating system: iMac  
Slicer version: 4.10.2  
Expected behavior: DWI Nifti file with 54 different diffusion-sensitizing gradient directions would convert to .nrrd and generate a file size similar to the sample data online (42 directions, 85MB) and run smoothly in UKF Tractography like the sample dataset.  
Actual behavior: DWI Nifti file with 54 different diffusion-sensitizing gradient directions generates a .nrrd file of 4.5MB and gives error when run in UKF Tractography (error: libc++abi.dylib: terminating). Strangely, my converted .nifti to .nrrd file of 4.5MB runs smoothly in other tractography modules, but not the UKF module.

Is it normal to have such a small .nrrd file size or could it be losing info during convert to .nrrd?

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**Author:** ![ljod](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/ljod/32/652_2.png) [@ljod](https://discourse.slicer.org/u/ljod)\
**Post date:** [August 17, 2019, 7:49pm UTC](https://discourse.slicer.org/t/dwi-convert-nifti-to-nrrd-gives-extremely-small-file-size-unable-to-run-in-ukf-tractography/8070/2 "2019-08-17T19:49:08Z")

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If you have DICOM please use the dcm2nii module instead to get nrrd.

What other error text appeared before that last error?