| DICOM PS3.4 2025b - Service Class Specifications |
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The Application Entity that claims conformance to this SOP Class as an SCU shall be permitted to invoke the following operations and the Application Entity that claims conformance as an SCP shall be capable of providing the following operations.
This operation allows an SCU to get information about a specific real-world Performed Procedure Step that is represented as a Modality Performed Procedure Step Retrieve SOP Instance by a Modality Performed Procedure Step Retrieve SCP. The operation is performed on a Modality Performed Procedure Step IOD. This operation shall be invoked through the DIMSE N-GET Service used in conjunction with the appropriate Modality Performed Procedure Step Retrieve SOP Instance.
The same SOP Instance UID is shared by all three Modality Performed Procedure Step SOP Classes. This means that the SOP Instance created and set using the services of the Modality Performed Procedure Step SOP Class can be retrieved using its SOP Instance UID within the service of the Modality Performed Procedure Step Retrieve SOP Class. Changes in its state can be notified by using its SOP Instance UID within the service of the Modality Performed Procedure Step Notification SOP Class. The SOP Class UID specified in the DIMSE N-GET request primitive shall be the UID of the Modality Performed Procedure Step Retrieve SOP Class.
An Application Entity may support the SCU role of the Modality Performed Procedure Step Retrieve SOP Class in order to obtain information about Performed Procedure Steps created by other Application Entities.
The Application Entity that claims conformance to this SOP Class as an SCU may choose to interpret the Attribute Values maintained by the SCP that the SCU receives via the operation of this SOP Class. The Application Entity that claims conformance as an SCP to this Modality Performed Procedure Step Retrieve SOP Class shall support the subset of the Modality Performed Procedure Step Retrieve Attributes specified in Table F.8.2-1.
Table F.8.2-1. Modality Performed Procedure Step Retrieve SOP Class N-GET Attributes
Attributes (0040,1006) Placer Order Number/Procedure and (0040,1007) Filler Order Number/Procedure were previously defined in DICOM. They are now retired (see PS3.3-1998).
Attributes (0040,2006) and (0040,2007) were previously defined in DICOM. They are now retired (see PS3.3-1998).
The Radiation Dose Module was previously defined in DICOM. This is now retired (see PS3.3-2017c).
The SCU uses the N-GET Service Element to request the SCP to get a Modality Performed Procedure Step Retrieve SOP Instance. The SCU shall specify in the N-GET request primitive the UID of the SOP Instance to be retrieved, which is a UID of a Modality Performed Procedure Step SOP Instance. The SCU shall be permitted to request that Attribute Values be returned for any Modality Performed Procedure Step Retrieve SOP Class Attribute specified in Table F.8.2-1. Additionally values may be requested for optional Modality Performed Procedure Step IOD Attributes.
The SCU shall specify the list of Modality Performed Procedure Step Retrieve SOP Class Attributes for which values are to be returned. The encoding rules for Modality Performed Procedure Step Attributes are specified in the N-GET request primitive specification in PS3.7.
In an N-GET operation, the values of Attributes that are defined within a Sequence of Items shall not be requested by an SCU.
The SCU shall be capable of receiving all requested Attribute Values provided by the SCP in response to the N-GET indication primitive. The SCU may request Attribute Values for optional Attributes that are not maintained by the SCP. In such a case, the SCU shall function properly regardless of whether the SCP returns values for those Attributes or not. This Service Class Specification places no requirements on what the SCU shall do as a result of receiving this information.
The N-GET operation allows the SCU to request from the SCP selected Attribute Values for a specific Modality Performed Procedure Step SOP Instance via a Modality Performed Procedure Step Retrieve SOP Instance. This operation shall be invoked through the use of the DIMSE N-GET Service used in conjunction with the appropriate Modality Performed Procedure Step Retrieve SOP Instance that equals the Modality Performed Procedure SOP Instance. The SCP shall retrieve the selected Attribute Values from the indicated Modality Performed Procedure Step SOP Instance.
The SCP shall return, via the N-GET response primitive, the N-GET Response Status Code applicable to the associated request. A Failure status shall indicate that the SCP has not retrieved the SOP Instance. Contingent on the N-GET Response Status, the SCP shall return, via the N-GET response primitive, Attribute Values for all requested Attributes maintained by the SCP.
Table F.8.2-2 defines the specific Status Code values that might be returned in a N-GET response. See PS3.7 for additional response Status Codes.
| DICOM PS3.4 2025b - Service Class Specifications |
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