draw lines on DICOM image with vtkImageViewer2

Hello, friends

I’m trying to draw lines on DICOM CT image.
vtkImageViewer2 is my prefer to display the DICOM image. And I need to draw lines on the displayed image too, but it seems could not work.
I found that vtkImageActor works, and if vtkImageMapToWindowLevelColors involved, which means the follow code used, then the lines will be covered by the image as vtkImageViewer2 did.

Code:
vtkSmartPointer imageActor = vtkSmartPointer::New();

imageActor->SetInputData(reader->GetOutput); // reader is an instance of vtkDICOMImageReader

vtkSmartPointer windowLevel = vtkSmartPointer::New();
imageActor->GetMapper()->SetInputConnection(windowLevel->GetOutputPort());

windowLevel->SetWindow(2000);
windowLevel->SetLevel(200);

m_pRender->AddActor(imageActor); // m_pRender is an instance of vtkRenderer;

Would you help me on this issue, please?