DICOM PS3.3 2024c - Information Object Definitions

C.17.5 Observation Context Encoding

Observation Context describes who or what is performing the interpretation (observer context), whether the examination of evidence is direct or quoted (quotation mode), what procedure generated the evidence that is being interpreted (procedure context), and who or what is the subject of the evidence that is being interpreted (subject context).

Initial Observation Context is defined outside the SR Document Content Tree by other Modules in the SR IOD. The Patient Module specifies the default Subject Context, the General Study Module specifies the default Procedure Context, and the SR Document General Module specifies the default Observer Context. The default context has the meaning "this Structured Report was produced by the observer identified in the SR Document General Module, using direct observation, for the procedure identified in the General Study Module, and is about the patient identified in the Patient Module." Observation Context defined by Attributes in these Modules applies to all Content Items in the SR Document Content Tree and need not be explicitly coded in the tree. The initial Observation Context from outside the tree can be explicitly replaced for the entire tree, or for any sub-tree.

Observer Context is set from the Author Observer Sequence (0040,A078), if present, or secondarily from the Verifying Observer Sequence (0040,A073). If neither is present, the Observer Context is undefined.


In the absence of Observer Context, it may be presumed that the observations were generated by or with the equipment identified in the General Equipment Module.

The Procedure Context is set from the Study Instance UID (0020,000D), Study ID (0020,0010), Accession Number (0008,0050), and Procedure Code Sequence (0008,1032) of the General Study Module. The Referenced Request Sequence (0040,A370) might include an Item with the same Study Instance UID that further elaborates the Procedure Context, e.g., providing Placer Order Number / Imaging Service Request (0040,2016) and/or Filler Order Number / Imaging Service Request (0040,2017). If the Referenced Request Sequence includes Items with different Study Instance UIDs, those shall be treated as Procedure Context only if explicitly encoded in the Content Tree.

Medical or clinical characteristics of the patient specified in the Patient Study Module, such as in Attributes Patient's Size (0010,1020) and Patient's Weight (0010,1030), shall not be inherited by the Content Tree as part of the default Patient Context. Such characteristics must be specifically encoded in the Content Tree to be part of the Structured Report.


The Patient Study Module may be included in SR SOP Instances. As part of the Study IE shared by all SOP Instances within a Study, such inclusion should be consistent across all Instances. However, its purpose is to provide a minimum set of clinical context for the (initial) interpretation of the images or waveforms of the Study. An SR SOP Instance that documents the interpretation must explicitly describe the relevant clinical context in the Content Tree.

If a Content Item in the SR Document Content Tree has Observation Context different from the initial context already encoded elsewhere in the IOD, the context information applying to that Content Item shall be encoded as child nodes of the Content Item in the tree using the HAS OBS CONTEXT relationship. That is, Observation Context is a property of its parent Content Item.

The context information specified in the Observation Context child nodes (i.e., target of the HAS OBS CONTEXT relationship) sets the Observation Context of their parent node Content Item. Observation Context is encoded in the same manner as any other Content Item.

The Observation Context applies to all the by-value descendant nodes of that parent node regardless of the relationship type between the parent and the descendant nodes, until and unless the context of a descendant node is reset by other Observation Context Content Items. Observation Context shall not be inherited across by-reference relationships. The four dimensions of Observation Context (observer context, quotation mode, procedure context, and subject context) may be reset independently; e.g., resetting the subject context does not reset the observer or procedure context, or the quotation mode. See the example in Figure C.17.5-1.


For example, the "subject context" may be defined by attaching an appropriate Content Item to the root node with a HAS OBS CONTEXT relationship. This "subject context" then applies not only to the root node, but to all its descendants, until such time as a Content Item explicitly replaces the "subject context" attribute, the new value of which is then inherited by all of that nodes descendants.

Observation DateTime is not included as part of the HAS OBS CONTEXT relationship, and therefore is not inherited along with other Observation Context. The Observation DateTime Attribute is included in each Content Item, which allows different observation dates and times to be attached to different Content Items.

The IOD may specify restrictions on Content Items and Relationship Types that also constrain the flexibility with which Observation Context may be described.

The IOD may specify Templates that offer or restrict patterns and content in Observation Context.


  1. Node 2 inherits any Observation Context of Node 1, which is then extended or replaced by the additional Observation Context defined in Nodes C1 and C2 (that is C1 and C2 are properties of 2).

  2. Node 3 and its descendents inherit the Observation Context of Node 2, which includes C1 and C2.

  3. Node 4 inherits the Observation Context of Node 2, which includes C1 and C2.

Definition and Inheritance of Observation Context (Informative)

Figure C.17.5-1. Definition and Inheritance of Observation Context (Informative)

DICOM PS3.3 2024c - Information Object Definitions