# How to easily turn a hollow segmentation into a solid (blood pool) segmentation

**URL:** <https://discourse.slicer.org/t/how-to-easily-turn-a-hollow-segmentation-into-a-solid-blood-pool-segmentation/16017>\
**Category:** Support\
**Tags:** segmentation\
**Created:** [February 16, 2021, 8:04pm UTC](https://discourse.slicer.org/t/how-to-easily-turn-a-hollow-segmentation-into-a-solid-blood-pool-segmentation/16017 "2021-02-16T20:04:37Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![Jezza](https://avatars.discourse-cdn.com/v4/letter/j/dfb087/32.png) [@Jezza](https://discourse.slicer.org/u/Jezza)\
**Post date:** [February 16, 2021, 8:04pm UTC](https://discourse.slicer.org/t/how-to-easily-turn-a-hollow-segmentation-into-a-solid-blood-pool-segmentation/16017/1 "2021-02-16T20:04:37Z")

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Operating system: macOS Catalina 10.15.7  
Slicer version: 4.11 20200930

Hi,

I’m aware that it is possible to turn a hollow segmentation (e.g artery) into a solid (blood pool) version. This is done using the following:

- Logical operators effect, Invert operation =\> Apply
- Islands effect, Keep largest island =\> Apply

If I erase parts of my original segment, this technique no longer works, because the “invert” tool will **still** appliy over the original segment volume, meaning that the inverted segment will not be an _isoltated island_ that can be removed using the “keep largest island” tool.

I want to know how to control the target volume of the “invert” tool. How can I adjust it so that it matches my modified segmentation which no longer has the same volume as it originally had?

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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:** [February 16, 2021, 8:09pm UTC](https://discourse.slicer.org/t/how-to-easily-turn-a-hollow-segmentation-into-a-solid-blood-pool-segmentation/16017/2 "2021-02-16T20:09:21Z")

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I would recommend to delete the “bridges” at the opening of the vessel to isolate the vessel lumen from the background. You can use Paint or Scissors effect for this.

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**Author:** ![Jezza](https://avatars.discourse-cdn.com/v4/letter/j/dfb087/32.png) [@Jezza](https://discourse.slicer.org/u/Jezza)\
**Post date:** [February 16, 2021, 8:26pm UTC](https://discourse.slicer.org/t/how-to-easily-turn-a-hollow-segmentation-into-a-solid-blood-pool-segmentation/16017/3 "2021-02-16T20:26:03Z")

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Hi Iassoan, could you clarify what you mean by “bridges”? Once I’ve inverted my model it becomes very hard to find the section I need to delete. Since my vessel is curved, I’m forced to make the modifications in the 3D window to be accurate.

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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:** [February 17, 2021, 4:34am UTC](https://discourse.slicer.org/t/how-to-easily-turn-a-hollow-segmentation-into-a-solid-blood-pool-segmentation/16017/4 "2021-02-17T04:34:25Z")

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You can make the segmentation semi-transparent so that you can clearly see all the vessel endpoints in the 3D view and you can snip the ends with Scissors effect.

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**Author:** ![Yvonne](https://avatars.discourse-cdn.com/v4/letter/y/3be4f8/32.png) [@Yvonne](https://discourse.slicer.org/u/Yvonne)\
**Post date:** [May 20, 2023, 8:03pm UTC](https://discourse.slicer.org/t/how-to-easily-turn-a-hollow-segmentation-into-a-solid-blood-pool-segmentation/16017/5 "2023-05-20T20:03:22Z")

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Hi Jeremy,

I’m hoping to do the same thing on an artery following your tips. I can do the inversion easily, however, after clicking on ‘keep the largest island’, nothing changes.

Have you encountered this before? Thanks in advance 🙂

Yvonne