Thursday, August 16, 2012

Top 10 DICOM Modality Worklist Issues

A DICOM modality worklist is retrieved by an imaging modality such as a CT, MRI, ultrasound, digital X-ray unit, or other imaging modality from a modality worklist provider, which can reside in the PACS, RIS or a separate device, such as a broker. Configuring the worklist on both sides, i.e. at the modality and on the worklist provider side, can be somewhat tricky to make sure that all pertinent information is available on the worklist, and does not contain too much or too little information. The pertinent information means that only studies that are to be scheduled for this device appear on the list, and does not contain studies to be done on other modalities. The worklist information therefore should be filtered and configured on both ends. Many times, the only way to find out the behavior is by using a modality simulator to predict and/or troubleshoot any issues with the modality worklist as described below. A demo is available here.
Below are the most common issues and configuration challenges:
1.       Where do I get my worklist from? This used to be a “no-brainer” as almost all PACS systems included a so-called broker, which would listen to the HL7 order messages, build an internal database for the scheduled appointments, and provide a DICOM worklist on demand. However, over the past few years, most PACS and department information systems, notably the RIS and CIS systems, have implemented this functionality, which is often referred to as a “broker-less” PACS or RIS. Unfortunately, the robustness and flexibility of these implementations have suffered and the number of worklist issues has increased. With regard to the worklist source, most modalities only support a single worklist, which is fine in most cases, but what if an ultrasound is used (and scheduled) by both cardiology and radiology requiring two work lists to be queried? Where is surgery scheduled and do I need to get another broker for those procedures? Same question applies for endoscopy exams, dentistry, and all other specialties that require images to be sent to the PACS.
2.       How do I provide a wireless worklist? Many ER and ICU departments, where portable exams are performed, use devices that can retrieve the worklist via a wireless router. This raises issues surrounding the security and authentication needed to protect the information. In addition, several incompatibilities have been reported with wireless devices and the worklist provider. A good rule is to test the wireless capability in all places you think one might have to use with the device prior to accepting a new unit.
3.       Which patient ID and physician should one use? The HL7 order message, which is used as the source for the worklist, has several Patient ID fields; an internal, external, social security number, medical record number, and even a location for the master patient index. The worklist provider needs to select the correct field to be used as the unique patient identifier in the PACS as it only has one field to contain that information. Additional ID’s may possibly be mapped in the so-called “Other Patient ID” field in the DICOM worklist. A similar problem occurs with the referring physician as the HL7 can contain several locations for the physician, which should be configured as well to make sure the right physician ends up in the corresponding DICOM field.
4.       How is the location of the modality that is to perform the study determined? In some cases, the modality field in the worklist is not sufficient to determine the location, but, rather, the modality needs to filter by station name and/or AE –Title in the worklist. The challenge is to deduce this information from the order information. For example, a bone density scanner could have the same modality identification (CR) as all of the other digital X-ray units in the main department. Another example is the distinction between an open and closed MR based on certain procedure information. The worklist provider needs to fill in the correct location based on information derived from the order.
5.       How to convert the invalid DICOM field and length values? For example, a backslash “\” is a valid HL7 character but is a control character in DICOM, and some of the HL7 fields have a different maximum length than their DICOM counterparts. Some of the coded values are also different, as an example, if the sex of a patient was unknown, identified with a “U” in HL7, it has to be converted to a value of “O” in the DICOM worklist to be valid.
6.       How to map modality and procedures? The modality identifier, e.g. MR, US, CT and other abbreviations, are not part of the HL7 order. The worklist provider needs to maintain a list of procedures and map it to the applicable modality. The correct part of the procedure description has to be mapped as well. I have seen problems where, instead of the full procedure description, the mnemonic or abbreviation was filled into the DICOM worklist while the modality expected otherwise, which eventually resulted in breaking hanging protocols at a workstation.
7.       How to configure the refresh rate of the worklist? The best manner to use for a worklist at a modality is for the technologist to refresh the list just prior to getting the next patient. Some devices are configured to poll the worklist provider with a configurable interval, for example every minute. If every modality is configured to poll the worklist provider, some of them are known for getting bogged down and overloaded. Therefore, unless required from a worklist perspective, e.g. when the worklist retrieval performance is creating issues, it is recommended to configure the modality to NOT use polling.
8.       Does the modality use single value matching or a broad query? Single value matching is used to retrieve a worklist item using an exact matching key such as an Accession Number or Patient ID. The advantage is that the resulting match is in most cases one, or at most a few, reducing the risk for incorrect selection. A broad query is used, for example, to request a worklist for a modality such as MR for today. If possible, single value matching is preferred.
9.       How to remove items from the worklist? Most institutions require a manual “exam complete” transaction by a technologist either at the PACS or RIS, which causes the entry to be removed from the worklist. If a modality has Modality Performed Procedure Step (MPPS) configured, this would be automatically performed by the MPPS transaction.
10.   How are modality request keys configured? Some worklist providers reject a query if they receive a matching request of one or more keys that they do not support. Even though this is non-standard behavior, it can be easily resolved by configuring the modality (if possible) to query with only the keys that are supported by the provider.
In conclusion, a modality worklist is often tricky to configure for both the modality itself and the worklist provider. Using a simulator can be not only helpful, but in some cases, the only way to find out its specific behavior.