DICOM Modality Worklist (MWL) makes patient demographic information from a RIS available at a modality, eliminating dual data entry and guaranteeing data integrity.

Modality Worklist is often used in two different manners by a device. Some devices retrieve the information in real-time, and some update the list by polling the IS on regular intervals.

Polling has the advantage of immediate availability of the information because it is cached at the local computer, but has a disadvantage that the information can be stale or out-of-date. An example - a patient might have canceled an appointment or have just been examined at another unit, which might not be reflected on the list. 

Another disadvantage of the polling method is the potential overhead to the IS and/or interface broker, which has to service all polling requests from multiple modalities. Which method is better depends on the workflow requirements of the department.