C. Image Set Selector Sequence Attributes

The Image Set Selector Sequence (0072,0022) contains sequence items that specify the DICOM attribute tags and values that shall be used to identify the image or other object set.

The Image Set Selector Usage Flag (0072,0024) indicates whether the attribute identified by the Selector Attribute (0072,0026) causes matching to succeed or fail if the attribute is not available in an image object.

Within a sequence item, the Selector Attribute (0072,0026) identifies a DICOM attribute tag that is likely to be present in image or other object instances that are desired for the Image Set. If it is a multi-valued attribute, the Selector Value Number (0072,0028) indicates which value is intended to be used for matching. The Selector Attribute VR (0072,0050) identifies the Value Representation of the Selector Attribute (0072,0026). The value of Selector Attribute VR (0072,0050) determines which attribute of the Hanging Protocol Selector Attribute Value Macro is required to specify one or more desired values for the DICOM attribute tag. If more than one value is specified for the attribute, or more than one sequence item is specified in the Selector Code Sequence Value (0072,0080), then image object instances with a corresponding attribute that matches any one of the values shall be included in the Image Set.

Note: The values used for the Selector Attribute (0072,0026) are intended to identify a type of image set via the general categories of modality, anatomy, procedure intent and/or reason. Therefore the values of the tags represented by Selector Attribute (0072,0026) are likely to be coded terms, enumerated values, defined terms or free text. The use of free text attributes is less desirable, because their values are less predictable for matching.

In an image object, some attributes occur at the top level, or nested within a Sequence or Functional Group Sequence, or both. In addition, a Private Attribute may be identified as a Selector Attribute (0072,0026). The attributes of the Hanging Protocol Selector Attribute Context Macro identify a Sequence, Functional Group Sequence, or Private Group context for the Selector Attribute (0072,0026).

The creator of a Hanging Protocol Instance uses this collection of attributes to identify one type of image set to which the Hanging Protocol is intended to apply. The user of a Hanging Protocol Instance (e.g., softcopy review workstation or pre-fetching application) uses this collection of attributes to match a specific image set to a Hanging Protocol, and/or to determine which image sets need to be retrieved in order to use a Hanging Protocol Instance. The Key Attributes to match against to obtain image sets are specified in the Selector Attribute (0072,0026) and its context in each sequence item.

If the value of the tag represented by Selector Attribute (0072,0026) contains a free text description (i.e., Selector Attribute VR = LO, SH, ST, LT, UT), whether exact or partial matching is used to identify a specific image instance when applying a Hanging Protocol Instance is implementation dependent.