<title>Hierarchical image storage management: design and implementation for a distributed PACS</title>

Abstract

Existing picture archiving and communication systems (PACS) lack intelligence in managing radiologic images distributed throughout individual PACS components (i.e. the acquisition, archive, and display subsystems), resulting in inefficient access to images. A multi-level storage system within our departmental PACS has been developed which minimizes access time for both current and historical images. The storage management system is based on a composite staging mechanism utilizing multiple storage media: redundant array of inexpensive disks (RAID), magnetic disks, erasable magneto-optical disks, and write-once-read-many (WORM) optical disks. Three levels of access to images at display stations are provided: (1) immediate access to both current and selected historical images via local RAID disks, (2) fast retrieval of images from archive subsystem's cache magnetic disks, and (3) retrieval of any historical images from long-term archive's magneto-optical disks and WORM disks. Mechanisms implemented in the system include: image routing, image stacking, image aging, HIS/RIS/PACS interfacing, image pre-fetching, studies grouping, and platter management. The storage management system for our distributed PACS was evaluated in terms of image access time at the display stations. With its multi-level storage architecture, the system demonstrated a 70% improvement in image access time compared with a centralized storage system. We conclude that fast access to radiologic images in PACS can be achieved through a well-designed, multi-level storage architecture.