Hi

I’m looking for help for two different issues, I’m a beginner in tractography so please excuse my naive questions.

# Question 1

I wish to warp a tractogram computed in native space to template space. I’m using transform files from ANTs and the corresponding MRtrix documentation .

- I checked the warpinit/ antsApplyTransforms /warpcorrect process with the images in native or template space and everything is fine. I can switch from Template → Native or Native to Template using mrtransform -warp.
- Using the tractogram , the results seems fine at first glance (I mean the position in space after warping) except for some tracks where I have some strange orientation. I’m suspecting a voxel resolution issue. I’m working with tensors , there are no ODFs in the processing.

### before transform (in native space)

### after transformation (in template space)

### here is the command line

```
tckgen dwi_den_modified.mif -algorithm Tensor_Prob -select 5000 -step 0.2 -angle 10 -cutoff 0.15 -maxlength 20 -minlength 1 -seed_image 16_Versus_Tracto//ROI.mif ${TRACTO_NAME} --force
tcktransform ${TRACTO_NAME} ${FOLDER_TRACTO_16}/inv_mrtrix_${NUM}_warp_corrected.mif ${TRACTO_MOVED_TO_T} --force
```

I’m using either FACT or Tensor_Prob of Tensor_Det but I’m not sure which step size should I use for each algorithm . The dwi , tensor and warps have a voxel resolution of 0.3 mm3

# Question 2

I wish to compare the following algorithm in native space : FACT, Tensor_Det & Tensor_Prob. Tensor_Det and Tensor_Prob give the same results but FACT differs a lot . Is there any tricks to match the tensor Prob algorithm ? Here is the command I use:

```
tckgen v1_1.nii.gz -algorithm FACT -select 5000 -step 0.2 -angle 10 -cutoff 0.15 -maxlength 20 -minlength 1 -seed_image 16_Versus_Tracto//ROI.mif 16_Versus_Tracto//Streamlines/stream_1_FACT_s5000_a20_angle10_co_l40.tck --force
tckgen dwi_den_modified.mif -algorithm Tensor_Prob -select 5000 -step 0.2 -angle 10 -cutoff 0.15 -maxlength 20 -minlength 1 -seed_image 16_Versus_Tracto/ROI.mif 16_Versus_Tracto//Streamlines/stream_1_PROB_s5000_a20_angle10_co_l40.tck --force
```

### figure with FACT in blue

### figure with FACT in blue and Tensor_Prob in green

Thanks in advance,

Valéry