Friday, August 14, 2009

What is PACS?

Imagine you writing a blog about, say, vegetarian Indian food recipes. The blog would consist of a collection of recipes (text data) and images of the food prepared (visual data). To transfer this information to other people, you would need some kind of system that would store the data and then be able to transfer it at will to other interested parties. This structure is the blog software and the server hardware. In other words, this is a picture archival and communication system, or PACS.

The History of Picture Archival and Communication System (PACS)

The concept of a PACS was first discusssed in the early 1980s. While no one individual can be credited with the full development of PACS, this article in Imaging Economics describes some of the contributions of early leaders in PACS development:
"Any image, anytime, anywhere—that's the mantra," says Reuben Mezrich, MD, PhD, describing the capability of the modern PACS (picture archiving and communications system). "But none of this could have happened without DICOM (digital imaging and communication in medicine).

"If you could give a Nobel Prize for DICOM, that would be a good thing," adds Mezrich, professor of radiology and chairman of the radiology department at the University of Maryland School of Medicine, Baltimore.

DICOM is a meticulously developed set of standards that allow systems to interface. It specifies how devices built in conformance with the standards react to commands and data being exchanged. DICOM, for instance, lets a CT scanner made by one manufacturer, an MRI scanner made by a second company, and an ultrasound machine made by a third company all communicate with the same PACS. It is because of DICOM that images from all three modalities, and others as well, can be displayed and interpreted at the same PACS workstation. The images can all be sent to the same PACS archive. DICOM is the computer standard that lets a PACS do its work.

If, as Mezrich suggests, a prize were given for DICOM, the recipient would most likely be Steven C. Horii, MD, who is now a professor of radiology and clinical director of medical informatics at the Hospital of the University of Pennsylvania, Philadelphia. By informal acclaim from his peers, Horii is credited with being the DICOM point man. He is cited for putting in the long hours and the blood, sweat, and perseverance that were necessary to DICOM's creation.
As with the development of any new standard, many people from many different backgrounds were involved to help create PACS and DICOM and secure their interoperability with other systems, which was the key to the success of the standard.

Picture Archival and Communication System (PACS) And Radiology

Almost all modern radiology services now use some kind of PACS system to manage their data and communicate with other services. The four basic components of PACS are:
  • Imaging Modality - CT, MRI, X-ray
  • Secure Network - to transmit data, typically over a VPN or SSL connection
  • Workstations - to view and manipulate images
  • Archives - to store and retrieve images
The most common format used on PACS is DICOM (Digital Imaging and Communication in Medicine). Although the format is widely used, it is not a strictly defined format. Vendors have the ability to define their own metadata tags for new features unique to their own systems. While this gives DICOM flexibility, it limits interoperability, as legacy viewers are unable to interpret novel metadata tags. Another issue for PACS is the integration of full field digital mammography (FFDM) into existing PACS systems versus the non-integrated solution of buying separate mini PACS workstations for digital mammography.

Regardless, PACS is key to the functioning of a modern filmless radiology department. Beyond simply proving image archival and display, a PACS must be able communicate with other hospital information systems, such as the hospital information server (typically where the full patient's EMR and biodata is stored) as well as the radiology information server (RIS).

The future of radiology is dependent on the continual development of PACS as a standard and as a tool that lets radiologists communicate their findings to their own colleagues, to other specialties, and ultimately to patients themselves.