A special case arises when the acquisition during a Protocol Stage is halted for some reason. For example, such a situation can occur if signs of patient distress are observed, such as angina in a cardiac stress exam. These criteria are part of the normal exam Protocol, and as long as the conditions defined for the Protocol are met the MPPS status is set to COMPLETED. Only if the exam terminates before meeting the minimum acquisition requirements of the selected Protocol would MPPS status be set to DISCONTINUED. It is recommended that the reason for discontinuation should be conveyed in the Modality Procedure Step Discontinuation Reason Code Sequence (0040,0281). Staged Protocols generally include criteria for ending the exam, such as when a target time duration is reached or if signs of patient distress are observed.
If a Protocol Stage is to be acquired at a later time with the intention of using an earlier completed Protocol Stage of a halted Staged Protocol then a new Scheduled Procedure Step may or may not be created for this additional acquisition. Workflow management recommendations vary depending on whether the care institution decides to create a new Scheduled Procedure Step or not.
Follow-up Stages must use View Numbers, Names, and Code Sequences identical to those in the prior Stages to enable automatically correlating images of the original and follow-up Stages.
K.5.5.2.1 Unscheduled Follow-up Stages
Follow-up Stages require a separate MPPS. Since follow-up stages are part of the same Requested Procedure and Scheduled Procedure Step, all acquired image SOP Instances and generated MPPS instances specify the same Study Instance UID. If the Study Instance UID is different, systems will have difficulty associating related images. This creates a significant problem if Modality Worklist is not supported. Therefore systems should assign the same Study Instance UID for follow-up Stages even if Modality Worklist is not supported. Figure K.5.5-2 shows a possible interaction sequence for this scenario.
In some cases a new Scheduled Procedure Step is created to acquire follow-up Stages. For example, a drug induced stress-echo exam may be scheduled because an earlier exercise induced stress-echo exam had to be halted due to patient discomfort. In such cases it would be redundant to reacquire earlier Stages such as the rest Stage of a cardiac stress-echo ultrasound exam. One MPPS contains the Image instances of the original Stage and a separate MPSS contains the follow-up instances.
If Scheduled and Performed Procedure Steps for Staged Protocol Exam data use the same Study Instance UID, workstations can associate images from the original and follow-up Stages. Figure K.5.5-3 shows a possible interaction sequence for this scenario.
