How do I interactively select region of interests on vtk?

I am using vtk with QT. Currently I read a series of Dicom Images using vtkDicomImageReader and visualize them with vtkImageViewer2 into slices.

Now I want to use mouse to pick some points and generate a closed curve on a 2D image slice, can anyone suggests what vtk method or class might be help?

I finally use vtkContourWidget class for points selection. This is a basic sample for using vtkContourWidget and this is the documentation of this class.

In my work, vtkContourWidget is binded with a vtkImageViewer2 using SetInteractor method. After binding it, I could use mouse click to pick some points and generate a contour line.