DICOM Storage Committment Information

What is DICOM Storage Commitment Service?

The DICOM Standard's Definition

Storage Commitment Service Class defines an application-level class-of-service which facilitates this commitment to storage. The Storage Commitment Service Class enables an Application Entity (AE) acting as an SCU to request another Application Entity (AE) acting as an SCP to make the commitment for the safekeeping of the SOP Instances (i.e. that the SOP Instances will be kept for an implementation specific period of time and can be retrieved). The AE where such SOP Instances can later be retrieved may be the SCP where storage commitment was accepted or it may be distinct from that SCP.

What Does This Really Mean?

When one device sends DICOM images to another device, this DICOM message is used to ask the recipient; "Here is the list of what I have sent. Are you really going to keep them for good?"

The answer better be "Yes, I will keep all of them." But for whatever the reasons that may not happen sometimes, for example."My disks are all full, sorry, I cannot honor your reuqest. Please try again later and be sure to hang on to the files until then!"

Why Would Anyone Need This?

Some modalities (i.e., scanners) use the commitment as a way of making its own list of purgeable data. In other words if the recepeient says "it has committed the data you just sent", then the modalities know that they can delete images from the machines to make room for more studies.

Some PACS vendor requires that sender will always use this feature that the image sents must be archived.

What Imorgon Do with This?

Imorgon uses this if the other system is ACUSON Sequioa to know that the study has ended, since Sequoia machines only sends the Study commitment message when the study is closed.  The DICOM standard did not say that's how this is used for, so this is not ture for most other scanners. Siemens scanners send the commitment on every image it sends. So in that case Imorgon does nothing functionally.  It sends response to the sender that with a message that it has received the commitment request and we will store them.

We have also begun supporting the DICOM Key Object Selection Document SOP Class to accomplish the post-consolidation of deleted images. Some newer models of scanners now supports this service to inform us which images were deleted.

Why Imorgon Server Dose Not Use This To Verify Archives

We have found out that often Storage Commitment is not a reliable way of confirming the existence of data on the archives. Some Storage Commitment classes are implemented basically as "dummy" operation and returns positive no matter what. 

A more reliable way to find out if the Storage has succeeded is to use the DICOM Query and check for sure if the PACS archives will return if a given DICOM object (image, reports) are on the system. Query is also available on almost all PACS archives.

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