Storage Commitment

What is DICOM Storage Commitment Service and why is it needed

Storage commitment (SCM) is a DICOM service that lets you verify if files that were previously sent to the PACS using the DICOM Storage Service were indeed stored by the application you sent it to. The SOP Class UID of this Service is “1.2.840.10008.1.20.1”. One can argue if it is necessary or not because when you send a DICOM image using C-STORE command and get a success status (0x0000) then it is supposed to be stored so the existence of Storage Commitment raises doubts about the meaning of that status in the first place. However, I can defiantly think of reasons for having such service, first because better safe than sorry and second because I already had some programming experience in the days when the DICOM standard was specified, Thanks god, we did make a long way since then. For example, some engineers, for the sake of efficiency and performance considerations, may have decided to first puts the files in a temporary storage or a queue, without even looking at their content and reply immediately with success and then later, when some batch or another thread processes the files in the queue and try to fill the database errors occur. I wouldn’t implement it this way, and I’ll give you reasons for that at the end of this post, but I did run into such implementations. The DICOM standard gives us the service but doesn’t go into the details of what is the implementation meaning should be but IHE does. IHE says that if your application creates instances and send it to somewhere, before deleting them from your local disk it should send a Storage Commitment and if all instances are OK, go ahead and make some space on your hard drive. Sounds like a good idea to me, it’s like double booking. Storage is the transaction and Storage Commitment is the reconciliation, Why not.

Storage Commitment Data Flow

All together SCM is pretty straight forward. All we need to do is to send a list of the instances and get back a reply saying which are in the PACS database and which are not, and that’s exactly how it works. Well, almost.