Monday, November 25, 2019

DICOM Modality Installation Checklist part 2

So you did all your homework prior to the new modality to be installed as described in part 1 of this post, i.e. you checked the conformance statements, used a simulator to query a worklist and send test images and checked if they display correctly at the PACS workstation. However, when you connect the new modality to the PACS it does not work. What do you do?

1.       Check connectivity: Ping the IP of the worklist provider and your destination(s), and then do a DICOM ping (aka Echo or Verification). The DICOM Verification feature might sometimes be hidden or only available under a service menu, but in many cases,  it is right there on the desktop or as a menu item. In rare cases there is no DICOM Verification implemented, shame on those vendors because it robs the service and support engineers from a very valuable tool. Failure of the network or DICOM ping indicate network issues, addressing (port, IP AE-Title) misconfiguration, or failure to add the device to the ACL list at the PACS.

2.       Assuming you have connectivity, but your images don’t show up on your PACS, the first line of defense would be to check the logs on either side, i.e. client and server or in DICOM lingo, SCU or SCP. The images at the PACS might have ended up “unverified” or “broken” which means that there is something wrong with the metadata or header. It is most likely an Accession number of ID integrity issue. Usually, these issues can be fixed with the standard tools available to the PACS administrator, however, in rare cases, you might need access to the PACS database to find out what happened, and in some very rare cases you might need to do an off-line validation of the metadata to see what causes the issue. The off-line validation will take the ages and runs a check against the DICOM data-dictionary. There are several DICOM validators that do this, both David Clunie has a validator and DVTK has a validator. In the case that the modality worklist does not show up, you again look at the logs and as a last resort, you will have to use a DICOM sniffer to see where the communication has broken down. A good illustration of such a problem was an Ultrasound of a major manufacturer which did not display the worklist, and only after using the sniffer we could prove that the information was actually received by the modality, and therefore, the fact that it was not displayed was a problem at that modality. I actually found out after running the validator that one of the worklist attributes had an illegal value and therefore the modality did not display it.

3.       Assuming you have a worklist at the modality, there might be information missing in the list or, there are too many entries or too few, meaning that the attributes used to filter the list were not applied correctly. In that case you will have to work with the interface specialist to map the HL7 orders to the worklist. Filters that determine what worklist items are displayed typically include the Modality, Scheduled AE-Title and/or Station Name. These have to be mapped from procedure codes, patient location and other elements in the HL7 order message.

4.       Assuming you are able to look at an image on a workstation, there could still be a display issue with the image ordering and view port positioning, which is typically determined by series and study descriptions as well as orientation information. If there is an image quality issue, there could be a problem with the pixel interpretation pipeline. The latter can be tested by using the test set developed for the IHE display protocol which have any possible permutation and combination of image types, photometric interpretation, presentation states, look up tables and other parameters impacting the display.

After troubleshooting these issues it should work! Congratulations on a job well-done. Remember with he proper training and tools you are empowered to solve these kind of tricky issues and problems by yourself instead of having to rely on your vendors who in many cases resort to finger pointing to each other. That is one of the very frequent reasons that IIP professionals show up for our training classes, in addition to getting additional career opportunities. Hope to see you at one of our training classes, see our schedule here.

Monday, November 18, 2019

DICOM Modality Installation Checklist.

One of the typical responsibilities of a PACS administrator is adding a new image acquisition
modality to the PACS system. It is also one of the more challenging tasks as it is often hard to predict how the device will interact as these are still not quite “plug-and-play.” To make it worse, this is often a visible and highly anticipated task, as in many cases the new modality has been expected for a long time. So, when it finally arrives at the loading dock, users want to see it up and working as soon as possible.
With proper preparation prior to and during the actual installation, the success rate of the install can be increased and the time to get it up and running can be greatly reduced and frustration kept to a minimum.

This is the check list I recommend prior to the install:
1.       Do a “paper validation” between the modality and its connections, i.e. DICOM worklist provider, DICOM destination(s) for image Store, Storage Commitment, Modality Performed Procedure Step, and Structured Reports. Get the DICOM conformance statements for these devices and compare them against each other. Make sure you get the right version of these conformance statements as functionality can differ substantially between different releases. Specifically look for the following in these documents:
a.       Make sure that there is support for the type of DICOM files (SOP Classes) you will be exchanging. Be aware of and look for support of the new “enhanced” SOP Classes such as for CT, MR, Angio, RF, breast tomosynthesis, IV-OCT and others.
b.       If you want to compress the images at the modality, make sure there is support of the type of compression at the source and destination(s) (JPEG lossless, lossy, Wavelet, MPEG for video, etc.)
c.       If you want to use Storage Commitment, make sure its behavior between the SCU and SCP matches with regard to the handling of the associations for the reply.
d.       If you want to use Modality Performed Procedure Step (MPPS), make sure that the implementation matches your workflow, for example, you don’t want to have MPPS report the study being complete if there are still images to be sent, processed, or imported.
e.       Match the worklist attributes between the modality and worklist provider and look for alternate mapping in case attributes might be missing on the modality side. An example would be to map missing patient weight or allergies in a Patient Comment field if that is required at the modality but not displayed.
2.       Do a “file validation” by asking the vendor to send you a CD with images, making sure that each type of image is on the CD. In addition, get sample Structured Reports, such as dose reports for CT or measurements for ultrasound and echo. Import these files on a test PACS, Voice Recognition and Dose management system and verify proper display of the images and measurements.  Make sure that the hanging protocols work at the workstations and if not, troubleshoot it to find what the cause is (study descriptions, body part, etc.)
3.       Do an “install validation” by using a modality simulator that is able to query a worklist using the same attributes as used by the new modality and simulate Store for the various file type to the test PACS. Simulate the Storage Commitment and MPPS. There are commercial modality simulators available (e.g. OT-DICE) as well as open source ones (DVTK). When doing the simulation, use the same IP address, port and AE-Title that the new modality would be using. It is strongly recommended to use best practices for the AE-Titles and port numbers, i.e. use an all caps AE-Title that indicates the institution, location and modality, and use the standard port number (11112) as assigned by IANA to DICOM devices. Work with IT so that you get a new, fixed IP address assigned for the new modality and make sure they configure the VLAN and routers to allow access.
If you have taken all these precautions, you should be able to swap out the simulator for the actual device, and the chances are that it might be “plug-and-play” assuming you addressed all the issues during the pre-install phase.
However, if it still does not work, you might want to do some troubleshooting using the tools as described in part 2 of this post.