DICOM PS3.3 2021d - Information Object Definitions

10.27 Reference Location Macro (Current)
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## 10.27 Reference Location Macro

This Macro allows a reference location in the context of a Patient or scan to be identified and described. E.g., the Macro may describe an anatomically defined location along the axis of a CT scan to prescribe the extent of a scan or reconstruction. The location might be internal to the Patient (and appear on a localizer image) or might be an external landmark (on which a laser is aligned).

Table 10.27-1. Reference Location Macro Attributes

Attribute Name | Tag | Type | Attribute Description
--- | --- | --- | ---
Reference Location Label | (0018,9900) | 1 | Brief user-readable label for the location.
Reference Location Description | (0018,9901) | 3 | Further elaboration of the Reference Location. The value may include a description of the relative anatomical location, the appearance of the feature or landmark, or how it can be identified.
Reference Basis Code Sequence | (0018,9902) | 1 | The anatomical feature or point of reference on which the reference location is based. Only a single Item shall be included in this Sequence.
>Include Table 8.8-1 “Code Sequence Macro Attributes” | CID may be defined in the Macro invocation.
Reference Geometry Code Sequence | (0018,9903) | 1 | Characterizes the geometry of the reference location (e.g., a plane or point). Only a single Item shall be included in this Sequence.
>Include Table 8.8-1 “Code Sequence Macro Attributes” | CID may be defined in the Macro invocation.
Offset Distance | (0018,9904) | 3 | Positive offset (in mm) from the Reference Basis to the actual Reference Location. See Section 10.27.1.
Offset Direction | (0018,9905) | 1C | Direction of the offset (in terms of patient position) from the Reference Basis to the Reference Location. Enumerated Values: SUPERIOR INFERIOR ANTERIOR POSTERIOR LEFT RIGHT PROXIMAL DISTAL MEDIAL LATERAL Required if Offset Distance (0018,9904) is present.

### 10.27.1 Offset Distance and Direction

An example of the use of offsets might be:

Reference Location Label | (0018,9900) | "1cm above Liver"
Reference Location Description | (0018,9901) | "1cm above the uppermost extent of the liver"
Reference Basis Code Sequence | (0018,9902) | (10200004, SCT, "Liver")
Reference Geometry Code Sequence | (0018,9903) | (128120, DCM, "Plane through Superior Extent")
Offset Distance | (0018,9904) | 10
Offset Direction | (0018,9905) | SUPERIOR

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DICOM PS3.3 2021d - Information Object Definitions