1.1. PACS and RIS Definitions
Picture Archiving and Communications Systems, more commonly known as PACS, enable images such as x-rays and scans to be stored electronically and viewed on screens, in such a way that doctors and other health professionals can access them, treat them and compare them with previous images at the touch of a button. The first implementation of such systems appeared in the 1990’s (Harno et al., 2002; Lebozec et al., 2000).
PACS deal with large amounts of data. This implies that they must be scalable. For most critical applications of PACS, the physician user needs to compare all the images of the patient history. Depending on the underlying technical architecture of the systems, this need can eventually lead to the necessity of prefetching of images.
PACS are usually run alongside with Radiological Information Systems, more commonly known as RIS. Such systems implement the workflow management of radiology centers including e.g. the management of patient identities, appointments, admission forms, and medical reports. This is illustrated on Figure 1.
Figure 1. Classical workflows of radiology data in health structures
As the tasks that they process are critical, PACS and RIS users ask for high service levels: no interruption, fast service and no data failure. Laws in most countries state that health structures must remain able to demonstrate a capacity to restore any medical image data until 20 years have passed since these image data were seen for the last time.
All this leads to high costs for the health structures for acquiring and maintaining PACS. Traditionally, health structures which were already running their own PACS were facing huge troubles with the complexity of the problem of archiving of images after several years of use because the cost of the necessary infrastructure to maintain was increasing exponentially.