In cooperation with BAZIS (Support Group HospitalInformation Systems at Leiden, The Netherlandsl, we started the design of a Picture Archiving and Communications System (PACS) a few years ago that contains a centralized image data base. By means of system modeling and measuring some performance parameters, we have discovered that such a system cannot provide the required response times. This is mainly because of equipment communication interfaces that are not fast enough and have a throughput that does not generally exceed 16 Mbits/second. By providing a parallet operating image buffer system, the problems related to the limited speed of the communication interfaces can be overcome. Moreover, by splitting the network into a number of subnets connected to each other by means of "bridges," the communications Ioad can be Iocally reduced, improving in this manner the response times. Our PACS contains a supervisor and one relational data base that relates patient data with image Iocations. A significant part of the report is concerned with the design of the high speed American College of Radiology-National Electronic Manufacturing Association transmission control protocol/internet protocol (ACR-NEMA TCP/IP) communications interface. The use of such ah interface eliminates the need for a Network Interface Unit, reducing in this manner communication delays and complexity. We have developed and have in operation for experimental purposes a small-scale PACS, consisting of a number of workstations, a relational data base and image buffers, all connected to a network that uses the ACR-NEMA TCP/lP protocols. This experimental PACS is used to provide input data to a PACS performance model, to validate this model, and to investigate alternative system configurations.

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This paper describes the design of a distributed database for a Picture Archiving and Communications System (PACS). This system consists of several relatively cheap workstations and a large optical archive and distributed database modules. The communication between the modules uses the same network as used to connect the system to the clients. Existing, working and available standards are used where-ever possible. This makes the system open and accessible in a multi-vendor environment such as hospitals. The distributed approach makes the total system flexible, cheaper, faster and when designed carefully, more reliable.

In recent years, we have designed and modeled several PACS configurations. Originally we started off with a PACS, comprising an archive and a centralised image data base, containing prefetched image sets to be used the current day. Performance modeling and experimentation [1] have shown us that such a system had an insufficient perfonnance in terms of response times. This was mainly due to the fact that an image base, implemented by a single computer, has an inadequate communication interface speed. We solved this problem by replacing the single image base in our design by a number of parallel operating image servers. In this paper we briefly describe the operation of PACS(1), about which more details can be found in another paper in these Proceedings (by the same author). PACS(1) has been equipped with a central relational data base, which correlates patient identification data with the location where the related images can be found. A performance model of this PACS(1) with response times is presented in this paper. PACS(1) has also been built using as much as possible, standard software and standard protocols, to keep the development costs down. From the standards used we mention: TCP/IP, SQL, X Windows and FTP. The recent development of powerful workstations has made itnow possible to eliminate the image servers in PACS(1) and integrate the functions ofthe image servers into the display stations. This rather simple and elegant design, called PACS(2), is presented in this paper together with a perfonnance model. Although the development of PACS (2) has not yet been completed, we found that the presently available high power workstations are still somewhat too slow to execute, with the required response times, simultaneously the high speed communication functions and the display functions. Special purpose hardware, to implement the TCP/IP protocol functions, will be introduced in the display workstation in order to reduce its workload and improve the response times. The design of such a TCP/IP interface, using transputer modules, is briefly discussed.

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