Digital Imaging and Communications in Medicine (DICOM)

5.3 DICOM Grammar: Value Representations 41
Fig. 6 Nesting DICOM data
I would recommend that anyone working on DICOM application development
avoid using the UN VR whenever possible. First, the other 26 VRs sufficiently
represent nearly all data types. Second, labeling the attribute type as
“unknown” seems more like an act of despair rather than a structured approach
to defining data types. Consider Big/Little Endian byte reordering as one such
example. You cannot perform this process for the UN attributes even when it is
needed because you just do not know whether the data is binary or text, or for
that matter, whether anything needs to be reordered at all.
To conclude, VRs play the most essential role in DICOM data structuring.
They connect DICOM to the outside world. VRs are word forms that DICOM
understands and speaks. But how do we translate our real-world data items
into VR? The answer is the DICOM Data Dictionary.