[vtkusers] Need some help to extract a portion from a 3D model

[Hayden Smith]

Dear vtkusers,
       I have attached one 3D model constructed from a number of images. I have attached the output with the email.I would like to discard the outer ring and only consider the inner ring as shown to the right of the original image marked with red color. How to discard the outer ring and work only with the interior tube? It would be good to find some way to discard the outer tube. Please provide some suggestion. I am a bit new in vtk. It would be good to help me with some similar kind of examples. I have attached some part of my code. 
 vtkImageReader v16
    v16 SetDataByteOrderToBigEndian
    v16 SetDataExtent 0 255 0 255 1 30
    v16 SetDataScalarTypeToChar
    v16 SetFilePrefix "images/"
    v16 SetFilePattern "%s%d.img"
    v16 SetDataSpacing 3.2 3.2 8.5
    v16 SetNumberOfScalarComponents 1
    v16 Update
　
vtkImageCast cast
    cast SetInputConnection [v16 GetOutputPort]
    cast SetOutputScalarTypeToUnsignedShort
    cast Update
 vtkContourFilter skinExtractor
    skinExtractor SetInputConnection [cast GetOutputPort]
    skinExtractor SetValue 0 40 
   skinExtractor Update
 
 
Regards,
Hayden.
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