The DICOM Storage Commitment service
The DICOM Storage Commitment service is an advanced DICOM service allowing a DICOM client application to request a commitment to a server for safekeeping of certain DICOM images and related data. It is complementary to the DICOM Storage service, and it is more focused on safekeeping of data with respect to this last service. In fact, when a SCU issues a normal DICOM Storage request to a SCP in order to transfer some DICOM data, and the SCP accepts this Storage request by returning a successful C-STORE-RSP message, there is the guarantee that the SCP has simply accepted the transferred DICOM data. However, there is no guarantee about the safekeeping of the transferred DICOM data by the SCP.
In the DICOM Storage Commitment service, a SCU may send a request to a SCP to commit to storage and safekeeping of a specific set of DICOM images and/or related DICOM data. This request is conveyed through the N-ACTION-RQ message. After accepting SCU’s request by returning a N-ACTION-RSP message, the SCP will then asynchronously notify the client about its commitment to store and safekeep the requested set of DICOM objects. The notification of storage commitment by the SCP will be successful only if the SCP commits to safekeep all the DICOM objects requested by the SCU in its previous N-ACTION-RQ message. If the SCP cannot commit to safely store one or more of the requested DICOM instances, then it will return a failure notification.
The notification of Storage Commitment by the SCP may happen also on a distinct DICOM association with respect to the one of the original Storage Commitment request by the SCU. This notification is conveyed through the N-EVENT-REPORT message.
Here is a possible usage scenario for the Storage Commitment service: in its daily activity, a DICOM modality acquires a set of DICOM studies, stores them in its internal storage, and also forwards them to a PACS server for longer-term archiving, through the DICOM Storage service. At a certain point in time, the modality wishes to delete one or more exams from its internal storage. However, before doing this, for safety reasons it sends a Storage Commitment request to the PACS server for all DICOM images which have been selected for deletion. It the PACS server answers by sending a successful Storage Commitment notification, then it means that all DICOM images which have been selected for deletion are safely stored in the PACS server’s archive, hence it is safe to delete them from the modality’s internal storage. Safe deletion is then completed on the modality side.