[Insight-users] Thresholding Windowing

[Luis Ibanez]

Hi Prabhat246,

The GDCM DICOM reader will take care of applying the Slope and Intercept
to the image intensity values for you.

For a typical iso-value to use for segmenting Bone from CT datasets you
can look at the Hounsfield Units:

http://www.itk.org/Wiki/ITK_Hounsfield_Units
http://en.wikipedia.org/wiki/Hounsfield_units

You could start with a value of 400, and experiment with values above
and below that in order to capture most of the structures that you
are looking for.

Please note that depending on how noisy you CT dataset is, you may
want to apply some smoothing before performing the iso-surface
extraction.

You may be interested in looking at the source code of the example:


          InsightApplications/Auxiliary/vtk/
                     itkReadITKImage3DSegmentShowVTK.cxx


    Regards,


        Luis


-----------------
prabhat246 wrote:
> I have a knee bone dataset in DICOM format. One image is attached with this
> email.
> If I take the int datatype then the intensity of pixel is between -3024 to
> +768(approx).
> 
> Can anyone tell me what is the correct method of doing
> windowing/thresholding??
> (I have read that all the pixel has to be multiplied by Rescale Slope and
> then added by Intercept.
> Rescale slope is 1 and rescale intercept is -1024.)
> 
> and what should be the isovalue for bone to run vtkMarchingCubes.
> (I am reading Dicomfiles with itk and then using vtkMarchingCubes.)
> 
> Thanks a lot.
> Prabhat http://www.nabble.com/file/p17704995/IM53 IM53