Specialization

The DICOM standard allows flexibility for implementers to accommodate data objects and types, as well as SOP class functionality, which are not covered by the standard. This allows equipment to exchange data using the DICOM framework, which would otherwise have to use proprietary communication protocols. For example, a manufacturer may build a data acquisition device, which generates a large amount of specialized acquisition information that is not included in the standard, but is necessary for advanced processing protocols on a workstation made by the same manufacturer.

Specialization is used when a standard attribute element is given restrictions for a particular application. Specialization is used often within the DICOM standard itself to restrict the range of values for an attribute in a particular image object. In the MR image object, for example, the number of bits allocated per pixel (0028,0100) is specialized to have a value of 16, while the general image module permits more options.

One needs to be aware, however, that some attributes can occur in multiple modules. For example, an attribute might occur in the general image and the ophthalmic image module (assuming we deal with ophthalmology images). The attribute description and type definition of the more specialized attribute specification always overrides the more general one. A good example of this is the modality attribute which, in the case of a Secondary Capture Image, is specified again in its specialized SC Equipment Module with a Type definition of 3 (Optional), while specified as Type 1 (required) in the General Series module. Type 3, in this case, over-rides Type 1. This is typically referred to as specialization.