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.