Deep archive demands continuous data migration strategy

November 5, 2001

Some harsh realities accompany PACS into a hospital. One is the chore of managing a digital image library in compliance with legal requirements when current systems may not be up to the task. While most hospitals are required to retain general,

Some harsh realities accompany PACS into a hospital. One is the chore of managing a digital image library in compliance with legal requirements when current systems may not be up to the task.

While most hospitals are required to retain general, nonmammographic radiologic images for seven years beyond the examination date, the laws are more demanding for pediatric images. These must be kept until the child's 18th birthday, plus a five-year statute of limitations.

Long-term stability of PACS archives presents a cluster of challenges, said Maria Elissa E. Blado, acting PACS team leader in diagnostic imaging at Texas Children's Hospital (TCH) in Houston, including the following:


?the limited and uncertain shelf life of high-density digital storage media
?the ability to maintain the hardware systems that read the data
?the short product life of software for accessing the images
?rapid development of higher density storage devices
?the exponential advancement of computer and network technology that fuels product obsolescence

As engineers at the Jet Propulsion Laboratory have discovered - to their dismay - data from early space missions housed on magnetic tape begin to deteriorate after only 30 years. No one really knows how much more (or less) durable CDs, DVDs, optical disks, and other electronic media will prove to be.

As an early (1992) adopter of PACS, TCH has seen a number of technologies influence its archive management strategy. Like nomads, the migrations never stop. A long-range strategy is required to ensure that electronic images acquired today can be retrieved and viewed 23 years from now, Blado said.

"Because we cannot guarantee the function of our digital archives for the full duration of our responsibility to maintain an image of record, we must be married to the concept of data migration," she said.

TCH's first archive, a write-once-read-many (WORM) technology, was abandoned after five years in favor of a low-density magneto-optical (MOD) media system, which was in turn upgraded to high-density drives.

"Once these filled to capacity, this undesirable situation forced us into shelf management of media," Blado said.

The current archive is based on a helical tape library with a seven-year exam capacity. Throughout the endless migration, Blado has struggled with the inadequate tools that are available on the market.

"The software tools for migrating data and for monitoring the integrity of our image database have not kept pace with the demands of our healthcare operation," she said. "They need dramatic improvement."