# 3D mode ROI (volume rendering)

**URL:** https://discourse.vtk.org/t/3d-mode-roi-volume-rendering/7705
**Category:** Support
**Created:** [January 24, 2022, 2:53am UTC](https://discourse.vtk.org/t/3d-mode-roi-volume-rendering/7705 "2022-01-24T02:53:35Z")
**Posts on this page:** 1
**Page:** 1

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### Author: ![sun](https://discourse.vtk.org/letter_avatar_proxy/v4/letter/s/49beb7/32.png) [@sun](https://discourse.vtk.org/u/sun)
#### Post date: [January 24, 2022, 2:53am UTC](https://discourse.vtk.org/t/3d-mode-roi-volume-rendering/7705/1 "2022-01-24T02:53:35Z")

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In MPR, I implemented the ROI extraction function using the vtkContourWidget widget.

But when I use vtkContourWidget in 3D mode (volume rendering), it doesn’t display well.

I want to draw a closed circle on the screen in 3D mode. How can I achieve this?

Is there a dedicated widget in VTK?

PS:I used the C# version of VTK. Cannot modify source code

 ![ROI](https://discourse.vtk.org/uploads/default/original/2X/d/da6cd5f676db187c8529c7ad4d232309e530d0fe.jpeg)