Modality upgrades may overwhelm PACS storage capabilities

Growth in imaging volume is often attributed to growth in patient volume. But the new capabilities that result from upgrades to imaging modalities, especially CT, can be an even greater factor, according to a presentation Thursday.

Peter M.A. van Ooijen, Ph.D., described an eight-fold increase in imaging volume at the the University Medical Center in Groningen, the Netherlands, resulting mainly from upgrades to imaging modalities, especially CT.

The University Medical Center in Groningen, the Netherlands, tracked the impact of modality upgrades on archive demands beginning in 2000. By the end of 2004, the amount of imaging data stored in the archive had increased from 1.2 to 5.4 terabytes, said Peter M.A. van Ooijen, Ph.D. Because the growth seems to be tracking linearly, the medical center anticipates that it will need more than 10 Tb of storage in 2008.

The number of patient exams entered into the RIS grew from 140,000 to 155,000 between during the same four-year period, van Ooijen said.

CT has been far and away the leader in generating additional imaging volume. The hospital installed a spiral CT in 2000, then added a four-slice, a 16-slice, an electron-beam scanner, another 16-slice, and, last November, a 64-slice scanner. CT image volume in 2000 was slightly less than 20,000 per month; in 2004 it averaged nearly 553,000 per month.

The growth was not anticipated, and the hospital's PACS vendor had downplayed the prospect, according to van Ooijen. It seems that when radiologists discover what they can do with the new scanners, they begin to order larger studies. One emergency room study totaled 10,000 images, he said.

CT is not the only source of growth, however. MR volume increased from 66,000 images per month in 2000 to 104,000 in 2004. In the same period, x-ray angiography increased from 1200 per month to 3700; ultrasound from 10,000 per month to 20,145; and mammography from 22 per month (priors that were digitized) to 627 (images were captured digitally beginning in 2003). Only computed radiography volume remained relatively constant at 10,338 per month in 2000 and 12,651 in 2004.

In addition to the new modalities, new postprocessing systems tend to compound the data volume problem, although they were not evaluated as a separate factor, van Ooijen said. Although some facilities place limits on which images are stored, all images generated at the University Medical Center are entered into the PACS.

Legal constraints and concerns about future legislation concerning the preservation of medical data have prevented the hospital from developing a system to purge old data, van Ooijen said. Even when patients die, removing old data can be so time-consuming and difficult that it is not done.

Complicating factors are the continuing evolution of storage technology and the need to migrate from one system to another, he said.

Although a hospital may carefully plan for the PACS and project its storage needs, the influence of upgrades and the introduction of imaging modalities lead to significant increases in storage requirements, the study concluded. In most cases, the predictions will be too low, and if the growth path is not adjusted, the PACS will run out of storage space.