What is PACS?
PACS stands for Picture Archiving and Communication System. On the most basic level, PACS integrates image acquisition modalities, workstation displays, the image archiving system, and the underlying network.
How are PACS images stored?
The PACS archive traditionally has been composed of short-term and long-term storage. Short-term storage is usually composed of redundant arrays of inexpensive (or independent) discs (RAID) arrays that provide quick access to image data. After a certain amount of time (3 to 30 days, depending on the size of the short-term archive), images from the short-term archive are moved to the long-term archive, which is usually composed of magnetic tape or magneto-optical media. Images cannot be viewed directly from the long-term archive. Instead, images need to be “fetched” from the long-term archive and copied back to the short-term archive before being viewed on a workstation. This compromise was made because of the high cost of RAID storage. The cost of RAID storage has decreased enough more recently so that several PACS archives are now being designed as “always online” systems. These new systems are composed only of RAID arrays, which essentially place all images in the short-term archive and eliminate the need for fetching.