Planning ahead ensures successful PACS operation

Establishing a filmless operation is rarely a trouble-free endeavor. But once the service is up and running, PACS administrators can make their lives easier by adhering to the maxim "be prepared." Speakers at this year's U.K. Radiological Congress offered two suggestions for preparedness: modeling likely demand on the archive and planning for IT systems failure.

The volume of data stored is not the only relevant parameter for determining whether a PACS will meet its users' needs, said Alun Davies, head of medical physics at the Great Western Hospital in Swindon, U.K. How often images are retrieved, when they are retrieved, and their age are all useful information in evaluating a PACS storage and networking system, he told delegates at the June meeting in Manchester.

Doctors at the Great Western Hospital have access to a fully populated digital image archive dating back to July 2001. With acquisition of about 180,000 examinations per year, the archive is growing steadily. Images are made available within the radiology department on dedicated diagnostic PACS workstations. Personnel working elsewhere onsite can review images on one of 1200 standard PCs, using a Web-based retrieval system.

Analysis of retrieval patterns during an eight-week period in 2004 revealed that 70% of images viewed were no more than a week old. The rapid fall-off was punctuated only by a slight increase in clinicians' requests for year-old images, presumably for routine follow-up. The analysis also noted differences in requesting patterns for various modalities. A significant number of nuclear medicine images were viewed up to two weeks after acquisition, while few ultrasound images were reviewed after the day of the scan.

"The vast bulk of data retrieval is being done through the main part of the day," Davies said. "Our network gives us 100 Mbit/sec to all devices, and a Gbit/sec connection to all radiologists' workstations, so it is coping very adequately with the demand."

Many hospitals in England may soon be linked to regional archives

as part of government-supported plans for a nationwide PACS rollout. But results from the Swindon hospital indicate that this investment might be better applied elsewhere.

"The benefit of cluster storage seems dubious, especially since we are-or someone is-going to be paying a high price to store these images, only to be able to retrieve them very slowly," Davies said.

Speaking at the same session, Alastair Jackson, PACS manager at Great Western Hospital, described how careful contingency planning can keep radiological images available during IT system downtime.

All PACS-related problems are first reported to the hospital trust's IT service desk. Dedicated IT staff then liaise with vendors and service suppliers to monitor downtime and manage it centrally. Meanwhile, potential PACS users are notified of the problem and the steps being taken to resolve it, Jackson said.

"You can't just tell somebody that the hospital network is down and expect them to sit around and wait for it to come back up. People have to know when they are going to be able to access the images again," he said. "If e-mail communication is not possible, we use porters to verbally distribute information to wards and clinics."

The least serious problem likely to occur is the unavailability of a modality work list. Clerical staff may have to be redeployed to input data manually, Jackson said. Additional checks of the accuracy of data entry may be necessary to prevent loss of images or their deployment to the wrong patient record.

Loss of the electronic patient record would be a greater inconvenience, although images remain available on the diagnostic PACS workstations and may also be accessible over the hospital Intranet.

"There are security issues involved, so it's not ideal. But in a situation where the unavailability of images is going to be prolonged, we do invoke that contingency, and a temporary username and password are issued," Jackson said.

If the PACS itself fails, images are retained on the modalities for up to a week. Point-to-point connections between laser printers and workstations enable hard copies to be printed and distributed to clinicians who are not working close to the radiology department. Local modality view is also possible in the event of complete network failure.

"There is a range of different ways in which PACS can fail, and each requires a different level of response, but a service can always be provided," Jackson said.