State-of-the-art PACS requires frequent upgrades

March 25, 2004

London's Hammersmith Hospital, one of the first institutions worldwide to install a PACS, went filmless in 1996, but the PACS it operates today bears no relation to the one that went live eight years ago. To maintain an up-to-date digital storage and

London's Hammersmith Hospital, one of the first institutions worldwide to install a PACS, went filmless in 1996, but the PACS it operates today bears no relation to the one that went live eight years ago. To maintain an up-to-date digital storage and retrieval system, staff have replaced dedicated workstations with soft-copy readers equipped with Web browsers, increased the short-term archive capability, and changed from a proprietary protocol to an open architecture.

These are just a few of the issues that must be addressed as the hospital continually strives to meet the challenges of maintaining a state-of-the-art PACS, said Dr. Nicola Strickland, a consultant radiologist at Hammersmith. Strickland spoke in a presentation at the Management in Radiology conference in Basel, Switzerland, in October.

When the PACS was first installed at Hammersmith, the largest available redundant array of independent disks (RAID) was 40 gigabytes, which seems almost laughable today, and the long-term archive had a capacity of 2 terabytes. To keep a significant number of studies online, the hospital had to create a sophisticated prefetching mechanism, called the storage "onion," that established different levels of archival protection for various categories of imaging studies. Unreported examinations had the highest status and were protected from falling off the short-term archive. Inpatient examinations were next in line, and outpatient examinations, which could be purged quickly from the short-term RAID, were placed on the outer layers of the onion.

From its first PACS Macintosh workstations, Hammersmith moved to a 250/260-Gb RAID and a radiology annotation and publishing system (RAPS) in 1998 to eliminate the cumbersome storage onion. In an even more comprehensive upgrade in 2001, the hospital eliminated its proprietary protocol and changed to an open 1-Gb-per-second system within the PACS and a 100-megabit-per-second system on a nonproprietary Ethernet. But even after changing switches, the hospital retained the original one-to-one dedicated network and optical fibers.

"We remained with an extremely high-grade system with high performance, which gets our images up in two seconds or less from first command to screen," Strickland said.

Hammersmith also changed from a Sun Microsystems server to the E 420R, which provides greater resilience, eliminating what Strickland called deadlocks or unaccountable system freezes that had occurred on an average of once a month.

Perhaps the most difficult aspect of the upgrade for clinicians was the shift from dedicated workstations and their supporting software to a Web browser. Despite the advantages of Web access, including the ability to generate slides directly through the PACS, clinicians did not initially accept the change because image processing was slower and less extensive. As a compromise, a few dedicated review workstations remain scattered throughout the hospital in the adult and neonatal intensive care units and the emergency department.

Additional upgrades made the hospital and radiology information systems HL7-compliant, which enabled DICOM modality work lists and decreased the number of inaccurate entries due to human error. The hospital also enlarged overall capacity to 576 Gb and replaced capital purchases with leasing arrangements.

Hammersmith is in the process of enhancing the PACS even further by shifting from optical disk jukeboxes to magneto-optical disks, which yield a total of 6.5 Tb of data and allow plain radiographs to be compressed at a ratio of 10:1 after they have been read. It is also establishing a speech recognition program and implementing electronic remote requesting. The hospital is generating a digital image teaching library that can be used with the diagnostic PACS workstations as well as Web browsers. This will enable clinicians to drag and drop an image directly from a reporting workstation and review it later on the Web.

The hospital is also creating a teleradiology link with two other National Health Service hospitals using a private virtual network on copper cabling. The system will require specifications for display time to be increased from two to three seconds and will necessitate separate short- and long-term storage devices at each hospital.

"We will be operating as a virtual hospital with an efficient workflow management such that we can do our work with any of the three hospitals," Strickland said.