[ITK] DICOM read-write intensity rescaling problems still present in ITK 4.5.2

[Eriksson, Mikael]

Hi all,

I'm using ITK 4.5.2, and recently noticed that in my work with DICOM-images, the intensities are rescaled even without any processing taking place between the read/write operations. I found this old thread from November 2007, http://www.itk.org/pipermail/insight-users/2007-November/024327.html, which does a good job explaining the cause and a workaround. The cause is that when reading the image volume, rescale slope and intercept is used to convert the stored unsigned integers (assuming the "Pixel representation"-tag is 0) to real-world values, but then these real-world values are written into the new DICOM-series, while the rescale-parameters are copied, so on the next read the real-world values will be different.

In the thread I posted, it says that a patch was added ahead of ITK 3.4 to correct the problem, but I'm using ITK 4.5.2 and still have the same issues. By using the workaround suggested by Eliana M. Vasquez Osorio,
     WriterType::DictionaryArrayRawPointer dicts = dcmreader->GetMetaDataDictionaryArray();
     WriterType::DictionaryArrayType::const_iterator itdict;
     for( itdict = dicts->begin(); itdict != dicts->end(); itdict++ )
     {
         WriterType::DictionaryRawPointer dicti = *itdict;
         //change 0028,1052,Rescale Intercept from -1000 to 0
         itk::EncapsulateMetaData<std::string>( *dicti, "0028|1052", "0" );
     }
I get the end result I want, so the intensities stay the same by manually setting rescale intercept to 0 in the new written series. I added a line to set the slope to 1 as well just to be sure, but so far in the data I've been working with the rescale slope has been 1 as for Eliana.

However, my question is: is this a good way to go about correcting this problem, and if it was corrected already in ITK 3.4, why then do I see the same behaviour with ITK 4.5?

Best regards,
Mikael


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Mikael Eriksson
R&D Physicist Trainee
Philips Medical Systems MR Finland, Feasibility studies
mikael.k.eriksson at philips.com<mailto:mikael.k.eriksson at philips.com>
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