# SlicerDMRI tractography measurements

**URL:** <https://discourse.slicer.org/t/slicerdmri-tractography-measurements/16468>\
**Category:** SlicerDMRI\
**Created:** [March 10, 2021, 2:05pm UTC](https://discourse.slicer.org/t/slicerdmri-tractography-measurements/16468 "2021-03-10T14:05:39Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![amymanson](https://avatars.discourse-cdn.com/v4/letter/a/13edae/32.png) [@amymanson](https://discourse.slicer.org/u/amymanson)\
**Post date:** [March 10, 2021, 2:05pm UTC](https://discourse.slicer.org/t/slicerdmri-tractography-measurements/16468/1 "2021-03-10T14:05:39Z")

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Hi, I was wondering if anyone could clarify the meaning of one of the measurement results produced when running Diffusion-\>Quantify-\>Tractography Measurements on DTI data?

The measurements produced are (among others) Num\_Fibres and Mean\_Length.

Presumably the Mean\_Length would be the mean length of the fibres measured. But I was wondering if Num\_Fibres was the total number of fibres picked up in the tractography or just the number which were sampled for mean length?

Thanks!  
Amy

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**Author:** ![zhangfanmark](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/zhangfanmark/32/4451_2.png) [@zhangfanmark](https://discourse.slicer.org/u/zhangfanmark)\
**Post date:** [March 10, 2021, 5:57pm UTC](https://discourse.slicer.org/t/slicerdmri-tractography-measurements/16468/2 "2021-03-10T17:57:22Z")

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Hi!

Num\_Fibers is the total number fiber streamlines of the input tractography file.  
Mean\_Length is the mean of the fiber lengths across all the fiber streamlines.  
There is no fiber sampling process here.

Regards,  
Fan

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**Author:** ![amymanson](https://avatars.discourse-cdn.com/v4/letter/a/13edae/32.png) [@amymanson](https://discourse.slicer.org/u/amymanson)\
**Post date:** [March 11, 2021, 10:42am UTC](https://discourse.slicer.org/t/slicerdmri-tractography-measurements/16468/3 "2021-03-11T10:42:54Z")

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Great, thank you!  
Amy