Hello all. I’m trying to do MRI segmentation on a very thin and round structure (knee cartilage). I was wondering if there is any to create a surface on a set of polynomial curves like this: [image] Looking forward to hearing from you. Mohammadreza

I thought this was an interesting use-case so I’ve been playing along at home. Here is a way to turn curves into a Surface Mesh (vtkPolyData), with controllable subdivisions. This isn’t as nice as a NURBS surface because it doesn’t subdivide between curves, but may be useful if distance between cu…

Thanks a lot, this is a very thin structure on non-isotropic MRI. I had tried Wrap Solidify, but it was not successful. That’s why I ended up with this idea.

What is your overall goal and plan? How will you use the surface? I ask because lofting splines is a non-trivial operation whereas working with segmentations is well studies and you can make it work without developing new tools.

My application is kind of Finite Element Analysis (not exactly; cartilages contact force analyses during physical activities using musculoskeletal modeling: opensim-jam/opensim-jam-release/examples/walking/graphics/walking_contact.gif at master · clnsmith/opensim-jam · GitHub ). So I need the cartil…

Okay, cool, yes, that helps. I would definitely supersample the segmentation heavily. Like use the crop volume to get just the cartilage are and the supersample as much as your computer can manage (or get a bigger computer) and then you may be able to paint with threshold and use smoothing to get …

Thanks again. There were two main issues in this approach: first, thresholding doesn’t work well for these kinds of MRI as this is not the best type for cartilage segmentation; second, the cartilages in children are so thin and narrow, the Brush or Draw tools were a nightmare. Overall, this approach…

Yes, that’s a classic CAD approach. There’s some support for doing things like that in Slicer extensions (surface markups) but I haven’t used them myself. Maybe someone else can chime in. If you are willing / able to do some coding I’m sure it’s doable with vtk or some python packages.

[image] pieper: surface markups I recall seeing NURBS surfaces in SurfaceMarkup extension. [NURBS surface editing in 3D Slicer] [image] GitHub - SlicerHeart/SlicerSurfaceMarkup: Extension to test the new grid surface markup with Extension to test the new grid …

Before I can chime in I’d like to understand. What you want to segment is this structure? [image] On how many slices does it appear in the MRI? I really have a hard time imagining how NURBS would be useful to represent this thin structure. Also, the problem with the NURBS in SurfaceMarkups is t…

Thanks all; What you want to segment is this structure? Yes, exactly, but the surface would be enough for me, so I don’t have to have a volume. This is a non-isotropic MRI, I already have it in 31 slices. I had some progress with curves and `vtkRuledSurfaceFilter`. This is not good yet, but the…

If you only want surface, then the SurfaceMarkup could be a way to go after all. What I could imagine is: Draw these open curves every few slices, in a way that they have the exact same number of control points Use a Python script to create a NURBS surface from this NxM grid Something like this: …

Segmentation using curves

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mrrezaie (Mohammadreza Rezaie) March 29, 2026, 2:29pm 24

Thanks for the suggestion; I’m now trying the alternative approach in more details. Since this is a different topic, I created a new post for that: Keep the hand-drawn segmentation after interpolation

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Segmentation using curves

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