In the MPPS SOP Instance, all the specific Attributes of a Scheduled Procedure Step or Steps are included in the Scheduled Step Attributes Sequence. In the Image SOP Instances, these Attributes may be included in the Request Attributes Sequence. This is an optional Sequence in order not to change the definition of existing SOP Classes by adding new required Attributes or changing the meaning of existing Attributes.
Both Sequences may have more than one Item if more than one Requested Procedure results in a single Performed Procedure Step.
Because of the definitions of existing Attributes in existing Image SOP Classes, the following solutions are a compromise. The first one chooses or creates a value for the single valued Attributes Study Instance UID and Accession Number. The second one completely replicates the Image data with different values for the Attributes Study Instance UID and Accession Number.
The modality may:
In the Image SOP Instances:
create a Request Attributes Sequence containing two or more Items each containing the following Attributes:
Requested Procedure ID
Scheduled Procedure Step ID
Scheduled Procedure Step Description
Scheduled Protocol Code Sequence
create a Referenced Study Sequence containing two or more Items sufficient to contain the Study SOP Instance UID values from the Modality Worklist for both Requested Procedures
select one value from the Modality Worklist or generate a new value for:
Study Instance UID
select one value from the Modality Worklist or generate a new value or assign an empty value for:
Accession Number
In the MPPS SOP Instance:
create a Scheduled Step Attributes Sequence containing two or more Items each containing the following Attributes:
Study Instance UID
Referenced Study Sequence
Accession Number
Requested Procedure ID
Scheduled Procedure Step ID
Scheduled Procedure Step Description
Scheduled Protocol Code Sequence
include the following Attribute value that may be generated during image acquisition, if supported:
Procedure Code Sequence
In both the Image SOP Instances and the MPPS SOP Instance
create a Performed Procedure Step ID
include the following Attribute values that may be generated during image acquisition, if supported:
Performed Procedure Step Start Date
Performed Procedure Step Start Time
Performed Procedure Step Description
Study ID