Is there a way to detect feature points of volume(vtkImageData) like in mesh(vtkPolyData)?

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Hi guys,
I’m trying to detect feature points from given input imagedata. More specifically, given CT scan of an object with visually-obvious concave and concave parts, return concave points and convex points.

The only way I can think of doing this is by:
1.convert imagedata to polydata using marching cube(given isovalue)
2.detect feature points using polydata. specifically, for concave/convex points, I can use curvature filter and easily find these feature points.

This is doable.The problem is that I lose precision during conversion from imagedata to polydata.
I don’t think I can calculate the curvature of imagedata, is it possible to detect concave/convex feature on imagedata itself?

Thanks!