Dcm4chee: Querying the Modality Work List (MWL) w/ the dcm4che-3 Toolkit
A modality work list (MWL) is an important concept in radiology IT.
An MWL can be thought of as a TODO list of radiology orders (usually stored on a server as part of a radiology information system, or “RIS”) that can be queried by different modalities (ie: medical imaging devices) over a network to figure out what procedures need to be performed next by a particular machine (or group thereof).
Each record in the MWL typically contains such info as patient info, specific scan(s) to be performed for said patient, scheduled date and location for each scan, and so on.
What if like me, you find yourself needing to query an MWL contained in a remote system (like dcm4chee) using a command line tool from the dcm4che toolkit, to say, pull up the complete list of upcoming MRI orders as currently understood by the system?
Using the dcm4che toolkit, the obvious tool is “findscu.” However, my first attempt:
findscu -c DCM4CHEE@HOST:PORT -m Modality=MR -M MWL --out-dir tmp
produced an empty result even though the MWL for MRIs was clearly non-empty – as confirmed by browsing the dcm4chee-web GUI:
After a bit of poking around online and experimenting, I was finally able to obtain the expected results with the following command:
findscu -c AET@HOST:PORT -m ScheduledProcedureStepSequence/Modality=MODALITY -M MWL --out-dir tmp
(Where for a default DCM4CHEE install we would have AET=DCM4CHEE and PORT=11112, and “MODALITY ” set to the modality code of interest, ie: CT, MR, etc.)
The trick was realizing that the actual modality of each order in the MWL was, in my case, nested inside a “sequence” called ScheduledProcedureStepSequence (the MWL info is represented in DICOM format which includes composite fields called “sequences” to represent multi-part data). This became apparent when viewing the order details view in dcm4chee’s web GUI, as per the screenshot below:
Presumably the reason for this nesting is to keep open the possibility that this scan be part of a sequence of scans (potentially of varied modalities) all pertaining to the same study, as opposed to an isolated study consisting of a single modality.