# Different wall thickness

**URL:** <https://discourse.slicer.org/t/different-wall-thickness/14018>\
**Category:** Support\
**Created:** [October 13, 2020, 7:57pm UTC](https://discourse.slicer.org/t/different-wall-thickness/14018 "2020-10-13T19:57:26Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![Andreas](https://avatars.discourse-cdn.com/v4/letter/a/ee7513/32.png) [@Andreas](https://discourse.slicer.org/u/Andreas)\
**Post date:** [October 13, 2020, 7:57pm UTC](https://discourse.slicer.org/t/different-wall-thickness/14018/1 "2020-10-13T19:57:26Z")

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Hello all,

when measuring my vessel models, I noticed that the wall thickness deviates significantly from the nominal thickness, for example if I want to print a vessel with a wall thickness of 0.5mm , I sometimes have wall thicknesses of 0.4mm to 0.6mm.

What is the reason for that?

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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:** [October 13, 2020, 8:36pm UTC](https://discourse.slicer.org/t/different-wall-thickness/14018/2 "2020-10-13T20:36:23Z")

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Wall thickness must be a multiple of labelmap spacing. When you use Hollow effect, you can see both the requested and the actual wall thickness.

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**Author:** ![Andreas](https://avatars.discourse-cdn.com/v4/letter/a/ee7513/32.png) [@Andreas](https://discourse.slicer.org/u/Andreas)\
**Post date:** [October 13, 2020, 9:11pm UTC](https://discourse.slicer.org/t/different-wall-thickness/14018/3 "2020-10-13T21:11:57Z")

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Thanks for your answer.

Unfortunately, your explanation did not answer my question, so I can send you two pictures to illustrate the problem. If I want to print a wall thickness of 0,5 mm and the result varies from 0,4 mm to 0,6 mm, this is not satisfactory.

How does this deviation come about and how can the problem be solved?

 ![Different wall thickness](https://us1.discourse-cdn.com/flex002/uploads/slicer/original/3X/3/3/3341d6e65e02363deb861a67029c03fb3b89f19b.jpeg)

 ![7](https://us1.discourse-cdn.com/flex002/uploads/slicer/original/3X/9/d/9d29096867d11d92872fa3e879cbd9db8ef08588.jpeg)

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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:** [October 14, 2020, 12:22am UTC](https://discourse.slicer.org/t/different-wall-thickness/14018/4 "2020-10-14T00:22:57Z")

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You choose the labelmap spacing (in Crop volume module). For very high accuracy, you can choose labelmap spacing that is a magnitude lower than the minimum wall thickness, but it may result in prohibitively large labelmap, so you may need to choose a spacing that is just 4-6x smaller than the wall thickness.

You may have measurement error due to inspecting a cross-section that is not exactly orthogonal to the vessel centerline. You may also have error due to finite (and anisotropic) resolution of the 3D printer and minimum wall thickness limitations.

These modeling errors are rarely significant (because for example you have magnitudes larger errors due to uncertainty in patient-specific material properties _in vivo_), but if you need to reproduce thin walls very accurately then you can run [vtkLinearExtrusionFilter](https://vtk.org/doc/nightly/html/classvtkLinearExtrusionFilter.html) with [SetExtrusionTypeToNormalExtrusion](https://vtk.org/doc/nightly/html/classvtkLinearExtrusionFilter.html#a4dd01aa4140f5fceb2b2b415de84dcec) option on the exported mesh. The disadvantage of this approach is that mesh may self-intersect, but if the wall is thin enough then this is usually not a serious problem.

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**Author:** ![Andreas](https://avatars.discourse-cdn.com/v4/letter/a/ee7513/32.png) [@Andreas](https://discourse.slicer.org/u/Andreas)\
**Post date:** [October 14, 2020, 9:11pm UTC](https://discourse.slicer.org/t/different-wall-thickness/14018/5 "2020-10-14T21:11:00Z")

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Many thanks for the help, everything worked.

I wanted to ask how to hide the white coordinate system (white lines).

 ![white coordinate system](https://us1.discourse-cdn.com/flex002/uploads/slicer/original/3X/e/c/eccfb78d537fdcf2c6dc3d4fba7b6ba7419e6c89.jpeg)

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**Author:** ![muratmaga](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/muratmaga/32/3622_2.png) [@muratmaga](https://discourse.slicer.org/u/muratmaga)\
**Post date:** [October 14, 2020, 9:47pm UTC](https://discourse.slicer.org/t/different-wall-thickness/14018/6 "2020-10-14T21:47:06Z")

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You have two different white lines. The rectangles in the slice view are from an active, visible ROI. Set the visibility off in the `Data` module. You also have the bounding box enabled in the 3D viewer. You can also set that off using the little pin putton very upper left corner of your screenshot.