# Handling FA values \> 1 before voxel-wise TFCE analysis

**URL:** https://community.mrtrix.org/t/handling-fa-values-1-before-voxel-wise-tfce-analysis/8792
**Category:** Uncategorized
**Created:** [June 25, 2026, 3:05pm UTC](https://community.mrtrix.org/t/handling-fa-values-1-before-voxel-wise-tfce-analysis/8792 "2026-06-25T15:05:50Z")
**Posts on this page:** 1
**Page:** 1

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### Author: ![diana\_99](https://community.mrtrix.org/letter_avatar_proxy/v4/letter/d/0ea827/32.png) [@diana\_99](https://community.mrtrix.org/u/diana_99)
#### Post date: [June 25, 2026, 3:05pm UTC](https://community.mrtrix.org/t/handling-fa-values-1-before-voxel-wise-tfce-analysis/8792/1 "2026-06-25T15:05:51Z")

</div>

Hello everyone,

I am fitting the diffusion tensor with MRtrix3 and have found a small number of voxels with FA values greater than 1. In every voxel where FA \> 1, one of the tensor eigenvalues is negative.

The affected voxels account for approximately 0.2% of the voxels within my analysis mask, for each participant. Most appear isolated and include voxels within white matter.

My acquisition is single-shell, with one b=0 image and the remaining volumes at b=1000 s/mm². The preprocessing includes:

- denoising with dwidenoise

- Gibbs-ringing correction with mrdegibbs

- susceptibility, eddy-current and motion correction using Synb0-DISCO, TOPUP and eddy\_cuda --repol

- ANTs bias-field correction

- brain masking based on the final corrected b=0 image

The tensor and scalar maps are calculated as follows:

dwi2tensor dwi\_den\_preproc\_unbiased.mif dt.mif \

```
-mask mask.mif

```

tensor2metric dt.mif \

```
-mask mask.mif \\

-fa fa.mif \\

-adc md.mif \\

-ad ad.mif \\

-rd rd.mif \\

-value eigenvalues.mif \\

-num 1,2,3

```

I understand that FA \> 1 is possible and that the negative eigenvalue indicates a non-physical tensor estimate. However, I am unsure what the recommended practice is before conducting a group voxel-wise analysis with permutation testing and TFCE.

Thank you in advance!