PACS Network Traffic Control

PACS Network Traffic Control

Carrison K.S. Tong (Pamela Youde Nethersole Eastern Hospital, HK) and Eric T.T. Wong (Hong Kong Polytechnic Institute, Hong Kong)
DOI: 10.4018/978-1-59904-672-3.ch013
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Abstract

Economically speaking, it is interesting to see that over the years, the question as to whether PACS is cost-justifiable has not been easier to answer. The early work at the hospital of the University of Pennsylvania, as well as at Washington University in Seattle, provided some early numbers and a framework to use, however, a clear “savings-model” is still difficult to formulate. The challenge is that one cannot just look at how much is saved by eliminating film, but that the true savings lie more in the increases in efficiency. Productivity studies by the VA in Baltimore in the early 1990’s have helped in this regard. However, one has to realize that, as Dr. Eliot Siegel from the VA in Baltimore strongly advocates, one has to re-engineer a department and its workflow to make use of the advantages of this new technology to really realize the benefits. As one can imagine, the early PACS only replaced their film-based operation with a softcopy environment without emphasizing re-engineering. That brings us to one of the big “drivers” in this technology: network standardization. In the early 1980’s, there was no one single standard. Transmission Control Protocol and the Internet Protocol (TCP/IP) was just one of the several options available. The United States government was pushing for the Open Systems Interconnection (OSI) standard.
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Network Standards

Economically speaking, it is interesting to see that over the years, the question as to whether PACS is cost-justifiable has not been easier to answer. The early work at the hospital of the University of Pennsylvania, as well as at Washington University in Seattle, provided some early numbers and a framework to use, however, a clear “savings-model” is still difficult to formulate. The challenge is that one cannot just look at how much is saved by eliminating film, but that the true savings lie more in the increases in efficiency. Productivity studies by the VA in Baltimore in the early 1990’s have helped in this regard. However, one has to realize that, as Dr. Eliot Siegel from the VA in Baltimore strongly advocates, one has to re-engineer a department and its workflow to make use of the advantages of this new technology to really realize the benefits.

As one can imagine, the early PACS only replaced their film-based operation with a softcopy environment without emphasizing re-engineering. That brings us to one of the big “drivers” in this technology: network standardization. In the early 1980’s, there was no one single standard. Transmission Control Protocol and the Internet Protocol (TCP/IP) was just one of the several options available. The United States government was pushing for the Open Systems Interconnection (OSI) standard. The OSI was an effort to standardize networking that was started in 1982 by the International Organization for Standardization (ISO), along with the International Telecommunication Union (ITU). The OSI reference model was a major advance in the teaching of network concepts. It promoted the idea of a common model of protocol layers, defining interoperability between network devices and software.

However, the actual OSI protocol suite that was specified as part of the project was considered by many to be too complicated and to a large extent unimplementable. Taking the “forklift upgrade” approach to networking, it specified eliminating all existing protocols and replacing them with new ones at all layers of the stack. This made implementation difficult, and was resisted by many vendors and users with significant investments in other network technologies. In addition, the OSI protocols were specified by committees filled with differing and sometimes conflicting feature requests, leading to numerous optional features; because so much was optional, many vendors' implementations simply could not interoperate, negating the whole effort. Even demands by the USA for OSI support on all government purchased hardware did not save the effort.

Major manufacturers, notably General Motors, were also trying to enforce broadband instead of Ethernet standards. As a matter of fact, the first PACS by Philips used broadband technology. There were also “ad-hoc” developments using inventive solutions in the 1980’s, such as the one at Michigan State University, whereby images from three CT scanners were sent to the University diagnostic center for reading leasing bandwidth from the commercial CATV cable system; a predecessor to cable modems! The early versions of DICOM, called ACRNEMA, only specified a dedicated point-to-point connection, leaving it up to the manufacturer to exchange the data via their network of choice. It took about ten years for the network standard to emerge, something we take for granted now. Today, everyone uses the TCP/IP as the basis for network communication, making it easy for new developments at the physical level such as gigabit/sec Ethernet to be deployed.

As with all other communications protocol, TCP/IP is composed of layers (Yale, 1995):

  • IP - is responsible for moving packet of data from node to node. The Internet authorities assign ranges of numbers to different organizations. The hospital authority assign groups of their numbers to PACS departments.

  • TCP - is responsible for verifying the correct delivery of data from client to server.

  • Sockets - is a name given to the package of subroutines that provide access to TCP/IP on most systems

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