# Don't know how to use Fast marching

**URL:** https://discourse.slicer.org/t/dont-know-how-to-use-fast-marching/20721
**Category:** Support
**Tags:** segmentation
**Created:** [November 22, 2021, 9:39am UTC](https://discourse.slicer.org/t/dont-know-how-to-use-fast-marching/20721 "2021-11-22T09:39:38Z")
**Posts on this page:** 4
**Page:** 1

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### Author: ![Gabriella-Rus](https://avatars.discourse-cdn.com/v4/letter/g/e9bcb4/32.png) [@Gabriella-Rus](https://discourse.slicer.org/u/Gabriella-Rus)
#### Post date: [November 22, 2021, 9:39am UTC](https://discourse.slicer.org/t/dont-know-how-to-use-fast-marching/20721/1 "2021-11-22T09:39:38Z")

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Hi! I try to work with “fast marching” from segmentation extension but when I press initialize button, nothing happens. What I am doing wrong?

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### Author: ![chir.set](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/chir.set/32/66982_2.png) [@chir.set](https://discourse.slicer.org/u/chir.set)
#### Post date: [November 22, 2021, 10:27am UTC](https://discourse.slicer.org/t/dont-know-how-to-use-fast-marching/20721/2 "2021-11-22T10:27:00Z")

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Seed your segment first.

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### Author: ![Gabriella-Rus](https://avatars.discourse-cdn.com/v4/letter/g/e9bcb4/32.png) [@Gabriella-Rus](https://discourse.slicer.org/u/Gabriella-Rus)
#### Post date: [November 22, 2021, 10:30am UTC](https://discourse.slicer.org/t/dont-know-how-to-use-fast-marching/20721/3 "2021-11-22T10:30:21Z")

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:))) was the first thing I did.

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### Author: ![lassoan](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/lassoan/32/13_2.png) [@lassoan](https://discourse.slicer.org/u/lassoan)
#### Post date: [November 23, 2021, 5:19pm UTC](https://discourse.slicer.org/t/dont-know-how-to-use-fast-marching/20721/4 "2021-11-23T17:19:32Z")

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Try to follow this short tutorial, using the exact same data set, painting similar seed in a similar location. If it works then try to do things similarly in your data set.

If you run into problems then you may post a screen capture video or an example scene file (saved as .mrb) so that we can have a better idea why it does not behave as you expect.

Note that Fast marching works well for easy segmentation problems: when there is a very clear strong contrast difference between the object of interest and the background. For non-trivial segmentation tasks, you may get better results with “Grow from seeds” or “Local thresholding” methods - and there are a number of others. Let us know what you want to segment, on what imaging modality, for what purpose and we can make more specific recommendations.