Overview: Unique Identifiers

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Unique Identifiers (UIDs) provide the capability to uniquely identify a wide variety of items. They guarantee uniqueness across multiple countries, sites, vendors and equipment. This scheme is used in DICOM to uniquely identify items such as SOP Classes, image instances, network negotiation parameters, etc.

The UID identification scheme is based on the OSI Object Identification (numeric form) as defined by the ISO 8824 standard. All Unique Identifiers, used within the context of the DICOM Standard, are registered values as defined by ISO 9834-3 to ensure global uniqueness. The uses of such UIDs are defined in the various Parts of the DICOM Standard.

Each UID is composed of two parts, an <org root> and a <suffix>:

UID = <org root>.<suffix>

The <org root> portion of the UID uniquely identifies an organization, (i.e., manufacturer, research organization, NEMA, etc.), and is composed of a number of numeric components as defined by ISO 8824. The <suffix> portion of the UID is also composed of a number of numeric components, and shall be unique within the scope of the <org root>. This implies that the organization identified in the <org root> is responsible for guaranteeing <suffix> uniqueness by providing registration policies. These policies shall guarantee <suffix> uniqueness for all UID's created by that organization. Unlike the <org root>, which may be common for UID's in an organization, the <suffix> shall take different unique values between different UID's that identify different objects.

The <org root> "1.2.840.10008" is reserved for DICOM defined items (such as DICOM Transfer Syntaxes) and shall not be used for privately defined items (such as an Image Instance).

Although a specific implementation may choose some particular structure for its generated UIDs, it should never assume that a UID carries any semantics. Thus, a UID shall not be "parsed" to find a particular value or component. Component definition (for the suffix) is implementation specific and may change as long as uniqueness is maintained. Parsing UID's may jeopardize the ability to inter-operate as implementations evolve.

Note: For a listing of UIDs supported by DICOM, refer to the Default UID Table.