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Re: understanding DICOM workflow


On 15.01.2016 10:00, Sébastien Jodogne wrote:

>> There's a standard DICOM way of saying "remove this worklist entry"
>> (regardless of whether it is completed).
> This process is typically done by sending HL7 messages, not through
> DICOM messages.
> Maybe the N-DELETE from DICOM "normalized services" might be used for
> this purpose, but I'm not sure as I'm not an expert in that field. In
> typical workflows, such "normalized services" are mainly used for
> MPPS (N-CREATE to setup a worklist, N-SET to update a worklist after
> some acquisition).

Maybe I can help out here. In DICOM there is no dedicated network
service in order to request the removal of worklist entries. This is
usually highly workflow-specific.

Quite often, as you denoted, the DICOM MPPS service (using N-CREATE and
N-SET) is used by the modality to report that an acquisition has taken
place. MPPS also includes a reference to the original worklist job the
examination refers to (i.e. its "Scheduled Procedure Step ID"). This
information can and is (but not must!) be used in order to remove jobs
from the worklist in currrent RIS implementations. The N-DELETE message
is not defined in the context of the DICOM MPPS service.

Note that there may be worklist jobs which are not fulfilled at all
(e.g. plan for the patient examinations changed), or worklist jobs which
are fulfilled more than once (i.e. more than one MPPS status object
referenicing the original worklist job), so it is not always straight
forward to decide when to remove the worklist entry.

Often MPPS feedback is not available at all since the modality does not
support this DICOM service. Worklist support, on the other hand, is very
common in practice. One possible implementation is then to remove the
worlist entry some hours/days after it has originally been scheduled
(without knowing via MPPS whether it actually took place).

HL7 can be used (for everything and nothing:) but there is no standard
message for removing worklist entries which is often found in practice
(to my knowledge!).

Again I can recommend reading IHE Radiology SWF Profile which shows best
practice in terms of DICOM services and HL7 messages for a full
Radiology image acquisition workflow (there are other IHE profiles for
reporting, post-processing, ...).

DCMTK does not have a free MPPS implementation but OFFIS offers some
commercially (using the library to implement one yourself is not
difficult, though). The DVTK toolkit [1] offers some free
implementations though I personally found them overall not very convincing.

Hope that helps,

[1] http://dvtk.org/

Michael Onken, Open Connections GmbH

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