Finding the optimal picture archiving and communication system (PACS) architecture: a comparison of three PACS designs.

PURPOSE: At present, there are two basic picture archiving and communication system (PACS) architectures: centralized with a central cache and controller, and distributed with a distributed cache and central controller. A third architecture proposed here is an autonomous one with a distributed cache and no controller. This report will investigate the performance (as measured be central processing unit [CPU] and network load, scalability, and examination retrieval and display latency) of these three types.
METHODS: The distributed PACS architecture will be simulated using an IMPAX R3.5 (AGFA, Ridgefield Park, NJ) PACS, while the centralized design will be simulated using an IMPAX R4 (AGFA) PACS. The autonomous system will be designed and implemented in-house. The autonomous system consists of two types of entities: basic components such as acquisition gateways, display stations, and long-term archives, and registry servers, which store global state information about the individual PACS components. The key feature of the autonomous system will be the replacement of the central PACS controller by the registry servers. In this scenario the registry servers monitor the interactions between the components, but do not directly govern them. Instead each component will contain the application logic it requires and will use the state information from the registry servers to take the appropriate action, such as routing images, prefetching studies, and expiring images from near line cache. In addition the routing of examinations will be optimized to reduce the duplication of image data. Display stations will be categorized by specialty (neuroradiology, pediatrics, chest, etc) and will retrieve studies for display on demand from intermediate servers dedicated to the corresponding specialty. Studies will be routed only to the intermediate servers and not to display stations.
RESULTS: By distributing the application logic, an autonomous PACS architecture can provide increased fault tolerance and therefore increased uptime. In addition, the lack of a central controller and the use of intermediate servers improve the scalability of the system, as well as reduce CPU and network loads.