[Insight-users] Qs about reading and writing (DICOM) images

[Andinet Enquobahrie]

Hi Alexander,

>Hello all,
>
>I have some questions regarding reading and writing images. I am currently working on a file converter, that is able to read and write various ITK and VTK file formats.
>Here are my questions:
>
>1) Is there a possibility, to determine the component type of an images before defining the reader type? I want to be able to automatically detect images of the types "short", "unsigned short" and "char", or is this only possible with user interaction?
>  
>
Yes it is possible. Look at the following code fragment

  typedef itk::ImageIOBase::IOComponentType  PixelType;

  itk::ImageIOBase::Pointer imageIO =
    itk::ImageIOFactory::CreateImageIO( this->FileName.c_str(),
                                   itk::ImageIOFactory::ReadMode );

  imageIO->SetFileName( this->FileName.c_str() );
  imageIO->ReadImageInformation();

  PixelType pixelType = imageIO->GetComponentType();

Then you can check

  switch( pixelType )
    {
    case itk::ImageIOBase::UCHAR:
      {
       ......
      }
    case itk::ImageIOBase:CHAR:
      {
     .......
       }
etc ....

>2) Is it possible to write 12 bit DICOM images (i.e. 16 bit, of which only 12 are effectively used)? So far, when I write a "short" or "unsigned short" image, it is always stored with 16 bit, so the largest possible value is around 65k. In my opinion, I should somehow be able to set the "BitsStored" tag (0028,0101) to 12 and "HighBit" (0028,0102) to 11.
>
>3) How exactly is the "RescaleIntercept" tag (0028,1052) handled? When I read a DICOM image with the value -1000, I get pixels with negative values. Does this mean, the negative values are stored in the file? Or does it mean, that the positive values have been reduced by 1000 by the GDCMImageIO in order to get the Hounsfield values? In the latter case, is there a way to avoid this and write the tag to the output file instead?
>  
>
The answer is the latter.

The GDCM IO extracts/parses the slope and intercept parameters from the 
DICOM header and applies
these transformation parameters to the CT values automatically when 
DICOM image is read.

Take a look at "itkGDCMImageIO.cxx". Specifically, method 
GDCMImageIO::Read( void * buffer )

Hope that answers your questions

-Andinet


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