I'm working on a project that securely moves DICOM files from one facility to another (PACS to PACS link, much like a VPN but without all the associated headaches in management and maintenance etc) and over the last month we've moved about 500,000 images using a new DICOM server that we've developed in Go.
Roughly outlining the workflow:
+------ SOURCE LAN ------+----- INTERNET ---------+--------- TARGET LAN ----------+
PACS > Our DICOM gateway > Secure Online Presence > Our DICOM gateway > Target PACS
One thing that we've started to notice, is that PACS (various vendors) are sending to our DICOM gateway various DICOM files without any pixel data and are generally 2 - 10K in size. Sometimes these are classed as CTs, SRs etc which is one thing that we're looking into, but we are receiving files that are classed as Raw Data Storage (1.2.840.10008.5.1.4.1.1.66) with the same Study Instance UID as their associated image files (those with pixel data) but have their own SOP Instance UID. The Number Of Study Related Instances does include all files: a basic two image study, has - in all DICOM files - has a value of "3" in DICOM tag (0020,1208).
I can't find anything really explaining what these files really are, even in the DICOM Standard WWW site and on various boards. I'm beginning to think that perhaps these are vendor dependent files that may contain details on (for example) merging studies within PACS and this file is a reference to the merged study.
I'm guessing at this point, so wondered if anyone can give me any more information as to what these files are and - more importantly to me at this point in time - if they don't contain any pixel data, and they're being stored in a different PACS than that system where they were originally captured from, can I safely not transfer them through our system?
I appreciate that certain DICOM images won't contain pixel data: my understanding is that dose reports don't, for example, and even though I've yet to come across those specific files, I would imagine that they would have a SOP Class of either X-Ray Radiation Dose SR or Radiation Therapy Dose Storage, and not this rather "random" Raw Data Storage?
The DICOM standard defines the Raw Data IOD (the IOD specification linked by the SOP Class Raw Data Storage) very minimally, but intentionally so. According to PS3.5 C.19.1.1:
The Raw Data stored with the Raw Data Module consists of one or more Private Attributes that are vendor specific. No rules are specified about the content and format of the raw data.
Raw data is understood as the data produced by the device during acquisition, even before the processing required to create an image or voxel matrix. This is why it has no pixel data. If truly necessary, the only way to know how to inspect the raw data contents within these files is to consult the documentation from the respective vendors.
can I safely not transfer them through our system?
With that said, it is legitimate not to be interested in forwarding the raw data files. Once the raw data is processed, the constructed imaging files stand on their own for nearly all purposes. So yes, you can do that by setting up your storage SCP to never accept the Raw Data Storage abstract syntax during presentation context negotiation.