# Generate a study-specific unbiased FOD template

**URL:** <https://community.mrtrix.org/t/generate-a-study-specific-unbiased-fod-template/7839>\
**Category:** Uncategorized\
**Created:** [July 29, 2024, 5:37am UTC](https://community.mrtrix.org/t/generate-a-study-specific-unbiased-fod-template/7839 "2024-07-29T05:37:33Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![H.A.N.K](https://community.mrtrix.org/user_avatar/community.mrtrix.org/h.a.n.k/32/4793_2.png) [@H.A.N.K](https://community.mrtrix.org/u/H.A.N.K)\
**Post date:** [July 29, 2024, 5:37am UTC](https://community.mrtrix.org/t/generate-a-study-specific-unbiased-fod-template/7839/1 "2024-07-29T05:37:33Z")

</div>

Hi,

Can someone help me understand what I should type in for “PRE” here? What does “PRE” stand for “I know that “IN” represents the input.”

I am attempting to complete step #10 for my FBA:  
 ![pre](https://community.mrtrix.org/uploads/default/original/2X/6/60cf3930a3a11ca3ef7d3875e45489c8a0cd51b0.png)

[https://mrtrix.readthedocs.io/en/latest/fixel\_based\_analysis/st\_fibre\_density\_cross-section.html](https://mrtrix.readthedocs.io/en/latest/fixel_based_analysis/st_fibre_density_cross-section.html)

---

<div class="post-metadata">

**Author:** ![adsouza](https://community.mrtrix.org/user_avatar/community.mrtrix.org/adsouza/32/4571_2.png) [@adsouza](https://community.mrtrix.org/u/adsouza)\
**Post date:** [August 5, 2024, 3:35am UTC](https://community.mrtrix.org/t/generate-a-study-specific-unbiased-fod-template/7839/2 "2024-08-05T03:35:50Z")

</div>

Hi Hayat,

In the context of the subsequent `population_template` command, “PRE” usually refers to a prefix or a base name used to match corresponding files, such as FODs and their masks.

Here’s a summary of how to organise the data for the population template command:

- Ensure there is a directory containing your FOD files (or symbolic link to FOD files).
- Have a separate directory for the corresponding mask files (or symbolic link to mask files), with the same base name as the FOD file.

Depending on how the data is set up and if PRE is not applicable, it could be removed (i.e., only specify the output directory with no prefix in the `ln` command).

Ensure that only participants who should be included in the population template are copied or linked to the template FOD (or mask) directory 🙂

Hope this helps!  
Cheers,  
Arkiev

---

<div class="post-metadata">

**Author:** ![H.A.N.K](https://community.mrtrix.org/user_avatar/community.mrtrix.org/h.a.n.k/32/4793_2.png) [@H.A.N.K](https://community.mrtrix.org/u/H.A.N.K)\
**Post date:** [August 5, 2024, 11:08pm UTC](https://community.mrtrix.org/t/generate-a-study-specific-unbiased-fod-template/7839/3 "2024-08-05T23:08:00Z")

</div>

That’s super helpful thank you!