DICOM PS3.17 2019a - Explanatory Information

GGG.2.7 Other Examples

A wide variety of workflow methods are possible using the UPS SOP Classes. In addition to those diagrammed in the previous sections, a few more are briefly described here. These include examples of ways to handle unscheduled tasks, grouped tasks, append cases, "event forwarding", etc.

Self-Scheduling Push & Pull: Unscheduled and Append Cases

In radiation therapy a previously unscheduled ("emergency") procedure may be performed on a Treatment Delivery System. Normally a TDS performs scheduled procedures as a Performing SCU in a Typical Pull Workflow like that shown in GGG.2.2. A TDS that might need to perform unscheduled procedures could additionally implement UPS Push (as an SCU) and push the "unscheduled" procedure to the departmental worklist server then immediately set it IN PROGRESS as a UPS Pull SCU. The initial Push to the departmental server allows the rest of the departmental workflow to "sync up" normally to the new task on the schedule.

A modality choosing to append some additional images after the original UPS was completed could use a similar method. Since the original UPS can no longer be modified, the modality could push a new UPS instance to the Worklist Manager and then immediately set it IN PROGRESS. Many of the Attribute values in the new UPS would be the same as the original UPS.

Note that for a Pull Performer that wants to handle unscheduled cases, this Push & Pull approach is pretty simple to implement. Becoming a UPS Push SCU just requires N-CREATE and N-ACTION (Request Cancel) that are quite similar to the N-SET and N-ACTION it already supports as a UPS Pull SCU.

The alternative would be implementing both UPS Watch and UPS Event as an SCP, which would be more work. Further, potential listeners would have to be aware of and monitor the performing system to track the unscheduled steps, instead of just monitoring the departmental Pull SCP.

Self-Scheduling Performer

An example of an alternative method for handling unscheduled procedures is a CAD workstation that decides for itself to perform processing on a study. By implementing UPS Watch as an SCP and UPS Event as an SCP, the workstation can create UPS instances internally and departmental systems such as the RIS can subscribe globally to the workstation to monitor its activities.

The workstation might create the UPS tasks in response to having data pushed to it, or potentially the workstation could itself also be a Watch and Event SCU and subscribe globally to relevant modality or PACS systems and watch for appropriate studies.

Push Daisy Chain

Sometimes the performer of the current task is in the best position to decide what the next task should be.

An alternative to centralized task management is daisy-chaining where each system pushes the next task to the next performer upon completion of the current task. Using a workflow similar to the X-Ray Clinic example in GGG.6, a modality could push a task to a CAD workstation to process the images created by the modality. The task would specify the necessary images and perhaps parameters relevant to the acquisition technique. The RIS could subscribe globally with the CAD workstation to track events. Another example of push daisy chain would be for the task completed at each step in a reporting process to be followed by scheduling the next logical task.

Hand-offs, Fail-overs and Putting Tasks Back on the Worklist

Sometimes the performer of the current task, after setting it to IN PROGRESS, may determine it cannot complete the task and would like the task performed by another system. It is not permitted to move the task backwards to the SCHEDULED state.

One approach is for the performer to cancel the old UPS and schedule a new UPS to be pulled off the worklist by another system or by itself at some point in the future. The new UPS would be populated with details from the original. The details of the new UPS, such as the Input Information Sequence (0040,4021), the Scheduled Workitem Code Sequence (0040,4018), and the Scheduled Processing Parameters Sequence (0074,1210), might be revised to reflect any work already completed in the old UPS. By including the "Discontinued Procedure Step rescheduled" code in the Procedure Step Discontinuation Reason Code Sequence (0074,100e) of the old UPS, the performer can allow watchers and other systems monitoring the task to know that there is a replacement for the old canceled UPS. By referencing the UID of the old UPS in the Replaced Procedure Step Sequence (0074,1224) of the new UPS, the performer can allow watchers and other systems to find the new UPS that replaced the old. A proactive SCP might even subscribe watchers of the old UPS to the new UPS that replaces it.

Alternatively, if the performer does not have the capability to create a new UPS, it could include the "Discontinued Procedure Step rescheduling recommended" code in the Procedure Step Discontinuation Reason Code Sequence (0074,100e). A very smart scheduling system could observe the cancellation reason and create the new replacement UPS as described above on behalf of the performer.

Another approach is for the performer to "sub-contract" to another system by pushing a new UPS onto that system and marking the original UPS complete after the sub-contractor finishes.

Yet another approach would be for the performer to deliver the Locking UID (by some unspecified mechanism) to another system allowing the new system to continue the work on the existing UPS. Coordination and reconciliation would be very important since the new system would need to review the current contents of the UPS, understand the current state, update the performing system information, etc.

DICOM PS3.17 2019a - Explanatory Information