#544 Add support for Real World Value Mapping Sequence

[Kris Thielemans]

SPECT DICOM images use a different convention for recording slope and intercept than other modalities.

https://dicom.innolitics.com/ciods/cr-image/general-image/00409096/00409225 confirms that to get the real value, we need

RV = (Real World Value Slope) * SV + Real World Value Intercept

It appears that ImageHelper::GetRescaleInterceptSlopeValue does not handle the NM modality.

Some more information at https://github.com/UCL/STIR/issues/1123

[Mathieu Malaterre]

I believe I need to update this issue. Thanks everyone for comments. It turns out this is not a minor change in GDCM toolkit. This is a fundamental new addition to the toolkit.

Full description is at:

• https://dicom.nema.org/medical/dicom/current/output/chtml/part03/sect_C.7.6.16.2.html#sect_C.7.6.16.2.11.1.1

GDCM has always presented the Rescale Intercept/Slope values through the gdcm::ImageHelper API. Since Real World Value Intercept and Real World Value Slope are different in the way they should be applied, I cannot make the change without breaking fundamentally the whole toolkit.

Since the original post mention a reference to 'cr-image' please note that the proper way to find the attribute definitions of one particular IOD is to go through the following steps. First PS 3.4:

• https://dicom.nema.org/medical/dicom/current/output/chtml/part04/sect_B.5.html#table_B.5-1

which leads to:

• https://dicom.nema.org/medical/dicom/current/output/chtml/part03/sect_A.5.html

which in turns leads to:

• https://dicom.nema.org/medical/dicom/current/output/chtml/part03/sect_C.7.6.html#sect_C.7.6.1

I am going to make it a feature request for the next major release of GDCM.