DR places added demands on PACS

Existing PACS configured to support standard imaging modalities may not be capable of handling the added demands of digital radiography (DR), some industry experts warn.

Just because a site has installed a PACS that has been adequate and designed for the usual assortment of imaging modalities (ultrasound, CT, and MRI) does not mean that a radiology department can simply add DR without major resizings and enhancements to PACS equipment, said Larry Filipow, Ph.D., an assistant professor of radiology and diagnostic imaging at the University of Alberta.

These include the following:

?central processing unit capability
?RAM size
?redundant array of inexpensive disks (RAID) capacity
?archive capacity

"Chest imaging is often as much as 50% of a typical imaging department's general procedures workload, and general procedures account for about 70% of all imaging examinations, so the storage requirements very quickly become very demanding," he said.

A single uncompressed DR chest image, at about 2.5K x 3K pixels, with a bit depth of 12, will inhabit 15 MB of storage space, according to Filipow.

Then, if a second view (PA/Lat) is added, one routine uncompressed DR chest examination requires approximately 30 MB of storage space. Using a dedicated, fully realizable 10 Mb per second network, it will take 24 seconds to transmit both images from one device to another.

Since network bandwidth is only 30% of stated nominal speeds, you can triple the time to about 75 seconds. When images are automatically compressed by 2:1 (lossless), however, real-world transmission time drops to around 30 to 40 seconds for a 10Base-T Ethernet (10 Mbps) network, Filipow said.

Still, this is too long in a busy clinical situation, so the PACS will need to prefetch previous exams and autoroute the current exams to the radiologist's workstation to achieve clinical acceptance, he said.

"For LAN networks, 100Base-T (100 Mbps) is minimum," said Henri "Rik" Primo, director of medical solutions in the IS/PACS CN department at Siemens Medical Systems. "Gigabit is better for a busy department, but if a DR was to be installed in a remote imaging center, with low throughput or low exam volume, routing over a wide area network with a standard T1 line to the central facility could work."

In order to achieve adequate transmission speeds, facilities need to ensure that all interface cards, switches, and routers can operate at that speed, something that cannot routinely be assumed.