Automated Cache Purging

Feature Description

If the Imorgon Server is forwarding studies to your PACS for permanent archiving purposes, your Imorgon Server can operate in "Cache" Mode. This feature will remove older studies that were not viewed recently from the Imorgon Server's disks thereby making rooms for newer studies. We have designed this feature so that your clinical efficiency will not be lost due to missing priors.

How It Works.

The Imorgon Server continuously optimizes the server disk storage using the following programmed methods:
  • It scans the patient records on Imorgon server and see if there are patients who was never looked at for several months. The number of months is configurable. If you have a large cache disk space, this can be large; as large as several years. 
  • For each patient that were "never looked at recently" the Imorgon server performs DICOM Query to to make sure that every image to be deleted are indeed stored in the PACS archive. Please also note that if a patient has been included in Teaching File Folder the patient will permanently be non-eligible for automated purging. Studies in teaching files will never be deleted from the Imorgon Server until they are no longer referenced in any of the teaching folders.
  • If the studies are 100% in the archive (i.e., the identical number of images on both the PACS and the Imorgon Server) and the DICOM Query confirms that they can be retrieved, then the associated images are marked for deletion.
  • A separate daily cleanup process runs on a schedule which will clean up the images that were marked for deletion.


  • Q: Which order do you delete?
    • The system will always prioritize deletion from the oldest "un-revisited" studies. 

  • Q: What happens if the patient comes back the next day the images were deleted?
    • There is HL7 or Modality Worklist based pre-fetch mechanism. Therefore, just about all priors will be pre-loaded from the PACS well in advance of the arrival and review of the data.
    • It is also possible to trigger a retrieval manually from the workstation.

  • Q: I do not want to remove images that are already in the teaching files.
    • If you include studies in the Imorgon teaching folders, these studies will be locked, therefore will not be deleted automatically. 

  • Q: Will the Patient ID, Study Description etc be removed also?
    • No, the deletion only pertains to the images (also the series level if all the images are removed for a series. Series is a DICOM term referring usually to one acquisition session.) Patient and Study records will remain permanently on Imorgon workstation and the database will indicate the total number of "online" images locally on the Imorgon Server at any given time. There will not be a need for you to go to a PACS and look for patient that was ever performed on your Ultrasound PACS.

  • Q: There is a certain date prior to which I do not want to automatically purge studies because I actually do not know the state of the data in the PACS.
    • There are some customers who do not export studies to the PACS prior to a certain date. There is a date cut-off configuration on the Imorgon server and any studies performed before the cut-off date will not become a candidate for the automated deletion.

  • Q: Are you really using DICOM Query function and not Storage Commitment?
    • We have found out that the DICOM Query is most up to date and reliable method of finding if a given study and images are in the PACS, so by design we have chosen to implement this feature this way. We also found that some Storage Commitment implementations can be just dummy functions; always responding as if images were all committed. If using DICOM Query with a positive response of availability it will ensure that the images are also retrievable in the future.

  • Q: How Conservative Is Your Method?
    • The system operate in a very cautious fashion. First all of the operations are performed at the Patient Level. If there is any chance of discrepancy for a given patient then the entire purging decision will be deferred for the next decision cycle date and no further action will be taken for the entire Patient level. Therefore there will be no partial removal of studies or images for a given patient. Also, if there are less images in the PACS compared to the ones in Imorgon, again, there will not be any action taken to remove anything from that patient.

  • Q: What Happens if there is a power or system failure in the middle of these operations?
    • Removal operations are database driven therefore it can resume from where it left off.

  • Q: Will this overtax the PACS?
    • There is a throttling and back-off mechanism in the system so the operation will be performed at time periods when there is more resources available at a reasonable rate.
    • After a while, the DICOM Q/R activities will taper off to a steady state roughly equal to the number of new patients you receive per day.

  • Q: Can I Turn This Feature Off?
    • Of course. Just let us know. And if you would like to use your disks as Archives, we can discuss backup strategies.

  • Q: I don't want to delete studies from certain AE Titles.
    • Presently this feature is not in place, but it is certainly on our development roadmap.