- Email: [email protected]
An expert system for troubleshooting in a picture archiving and communication system
PERGAMON
Engineering Applications of Arti®cial Intelligence 11 (1998) 469±475
Contributed Paper
An expert system for troubleshooting in a picture archiving and communication system M. Wiltgen * Department for Medical Informatics, Statistics and Dokumentation, University of Graz, Austria Received 1 August 1997; accepted 1 June 1998
Abstract At the Department of Radiology of the University of Graz, a picture archiving and communication systems (PACS) is used in routine operation. The operation of the PACS is an essential part of the clinical routine. Failures which occur in one part of the system may spread out, and critically impair the routine work. To allow the operation of the PACS to be independent of the permanent presence of an EDP-expert, a rule-based expert system has been developed for trouble-shooting. This expert system makes use of standard techniques, and helps the PACS user, to eliminate problems and to guarantee smooth operation. # 1998 Elsevier Science Ltd. All rights reserved. Keywords: Expert systems; Picture archiving and communication systems; Trouble-shooting
1. Introduction With the development of imaging methods such as computed tomography (CT), magnetic resonance imaging (MR), digital subtraction angiography (DSA), digital radiography (DLR) and so on, new and successful diagnostic methods have been introduced in medicine. Starting with nuclear medicine, more and more of the imaging methods have either been digitized (for example; digital radiography) or, like CT and MR, have started as digital methods from the beginning. The number of digital images has increased continuously during the last few decades. Traditionally, hardcopies on ®lm are made from the digital images, and these hardcopies are used for archiving and reporting. Then, for the end-users of the diagnostic information (such as neurosurgeons, radiotherapists etc.), the image information is available on ®lm. The disadvantages of the use of ®lm are: (1) the high expenditure on the archive space (®lm folders are ®lling up whole rooms), (2) the loss of images during their distribution within the hospital, (3) the slowness of access to the images, and (4) the loss of information * Corresponding author. Tel.: 00 43 316 385 3587; Fax: 00 43 316 385 3590; E-mail: [email protected].
that occurs when a hard copy is made from a digital image. PACS (picture archiving and communication systems) have been developed to handle the increasing number of digital images (Meyer-Ebrecht, 1994; Giribona, 1991; Greinacher et al., 1990). In a PACS, the image-acquisition systems, the archive and the digital viewing stations are interconnected in a network, and the digital images are transferred via the network (that means without making a hardcopy) from the image-acquisition modalities to digital consoles, and to the digital archive. PACS implies the digital processing, archiving, transfer, display, etc. of image data, and this should, in principle, make hardcopies on ®lm unnecessary. The hoped-for advantages of PACS over conventional methods include several aspects: 1. ®nancialÐreduced costs for ®lms, archive space and personnel; 2. archivingÐbetter availability of images; experience has shown that in conventional ®lm archives, 25± 35% of ®lms are not available when requested (because they have been lent to somebody, are misplaced, etc.); 3. communicationÐfaster image transfer and simultaneous access from multiple points;
0952-1976/98/$ - see front matter # 1998 Elsevier Science Ltd. All rights reserved. PII: S 0 9 5 2 - 1 9 7 6 ( 9 8 ) 0 0 0 3 5 - 9
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M. Wiltgen / Engineering Applications of Arti®cial Intelligence 11 (1998) 469±475
4. interpretationÐthe image-processing capabilities of a PACS workstation, such as windowing, ®ltering, three-dimensional visualisation, quanti®cation, etc. might be an aid to diagnosis, because all the information in the images can be exploited. In a PACS, there is no longer a dependence on the locality of information, and simultaneous access to the images is possible from peripheral departments. The ®nal goal of PACS would be a completely ®lmless hospital (Akisada et al., 1993; Mosser et al., 1994). At the Department of Radiology of the University of Graz, a PACS runs as part of the daily routine (Wiltgen et al., 1993; Wiltgen et al., 1994). The PACS was integrated into the radiological department in cooperation with Siemens Erlangen, and its operation in routine work has been studied for a period of several years (Wiltgen et al., 1990). As a result of this experience, software has been developed to improve the handling and operation of the PACS. Since 1993, the PACS has been expanded by adding components based on the Siemens SIENET concept.
2. PACS con®guration The PACS in the Department of Radiology currently incorporates four CT-scanners, two MRI-scanners, one DSA, one DLR and one Ultrafast CT as modalities (see Fig. 1). In addition, it includes a radiography planning system, two reconstruction consoles, and several reporting and viewing consoles. Two archive units (320 GB online) with a total of three jukeboxes for optical disks (WORM) and another archive (52 GB online), mainly used for DLR images, serve as the long-term archive. The network is based on FDDI and Ethernet. The PACS consists partially of a Siemens SIENET PACS, with several components supplied by IMAGE DEVICE (located in the pedriatic radiology department), and, on the other hand, several components of the older PACS version. The SIENET modules are based on SUN SPARCstations, whereas the older parts are located on VAX systems. The PACS is connected with a radiological information system (RIS), so that the management of the image
Fig. 1. The PACS-con®guration at the Department of Radiology of the University of Graz. The con®guration connects several CT- and MRIscanners, a DSA and a DLR. The images produced are displayed on reporting consoles (MagicView), viewing consoles (PV) and special reconstruction consoles (GammaPlan). Dierent parts of the PACS con®guration (from dierent manufactures) are interconnected by gateways (HMG, Magic Link, ISI gateway, SPI spooler). Archive units (ISA) with jukboxes serve as an image store. The network is based on FDDI and Ethernet.
M. Wiltgen / Engineering Applications of Arti®cial Intelligence 11 (1998) 469±475
archive is done by the RIS, using patient data to select and retrieve the images. All the images produced from CT, MRI, UltrafastCT, DSA and DLR are routinely stored in the optical archives. The PACS is used for dierent tasks including archiving, retrieval of previous examinations, reporting of selected examinations on the digital reporting consoles, and image distribution to selected places within the hospital. 3. PACS software process structure The PACS is organized as a group of independent software processes, which communicate with each other. These processes run in the background, and provide access to the images and image data. The processes execute tasks such as: transferring images over the network (by the network process), conversion of images (by the norm process), submissions into databases, etc. The process structure is distributed over several computers. First, the processes are in a waiting state, and must be activated by a command from another process. The processes work simultaneously, and the sequence of processes operates as a pipeline; while the last images of an examination are still being transferred over the network, the ®rst images have already been submitted into the image database. The communication between the processes is administrated by the Siemens PACSNET/SPI toolkit, which complies with the ACR-Nema commands to request and transfer images (ACR-Nema, 1985). 4. Problem description A PACS plays an important role in organising the tasks of a radiological department, deeply in¯uencing the organisation and the infrastructure. The PACS is not stand alone equipment which runs independently from other equipment. Because many dierent components of the radiology department are interconnected in the network, failures that occur in one part of the PACS may spread out and hamper other, routine work (Wiltgen et al., 1991). Such failures can include both software and hardware failures, although a high proportion of them are software failures. Therefore, in this paper, the attention is mainly concentrated on this kind of problem. Some examples of such failures are: a software process is not active, the communication between two processes is interrupted, a device is full, etc. Then tasks performed by the PACS, such as archiving or image transfer, are impaired. If problems of this sort are not eliminated after a certain time, then extensive delays in the routine work may occur, or the routine may even become comple-
471
tely blocked. The PACS runs 24 h a day. Especially during the night and weekend shifts, when no system manager is present to localize and eliminate malfunctions, the routine work would be critically in¯uenced and impaired. Therefore, at least during the night and weekend shifts, it is important that malfunctions of the system can be eliminated by the users themselves. The PACS in Graz was one of the earliest pilot projects, and one of the ®rst systems running as routine (Wiltgen et al., 1995). From the beginning of the project it was of special importance to gain experience about the introduction of the PACS in a radiological department: how the work¯ow could be optimised, and which requirements were needed to guarantee a smooth operation. Experience with the routine operation of the PACS shows that most of the problems that occur can be localised and removed by the application of a de®ned set of rules. From the point of view of the radiographers, one of the requirements was that it should be possible for them to check out and handle the PACS, especially if malfunctions were to occur, and to obtain information about the state of the system. Therefore, a computer program has been developed to help the PACS user (who is generally not a computer expert) to easily localize and eliminate malfunctions during routine operation.
5. Troubleshooting with an expert system OPERAS (operating assistant) is a rule-based expert system for error detection and elimination in the PACS. It is an intelligent tool to provide PACS user support, and allows the user to recover the normal operating state of the PACS. This expert system makes the routine operation as independent as possible of the presence of an electronic data-processing expert. When the user consults the OPERAS program, OPERAS ®rst opens a dialogue with the user to gain information about the state of the PACS. Then the facts are analysed by condition±action rules, a hypothesis about the possible reason of the malfunction is formulated and either advice is given to the user on how to eliminate the problem, or the malfunction is eliminated automatically by the program. 5.1. OPERAS components The OPERAS program is based on condition±action rules. The knowledge base, covering the reasons for possible malfunctions, and how to eliminate them, is represented by heuristic rules. OPERAS consists of four main components (see Fig. 2): 1. a set of heuristic rules (object rules) for the localisation and elimination of malfunctions;
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act with the system. A rule of the ®rst kind can, for example, check whether a software process has started, or if there is an over¯ow in an image directory. A rule of the second kind can start the software process, etc. A part of the decision tree is shown in Fig. 3.
Fig. 2. Overview of the OPERAS components. The system consists of four main components: (i) a set of heuristic rules to localise and eliminate malfunctions during the routine work; (ii) a set of metarules for the selection of specialized groups of heuristic rules to check dierent components of the PACS; (iii) modules for the user dialogue and system checks; and (iv) variables that represent the actual state of the PACS.
2. meta-rules for the selection of tests; 3. modules for the dialogue with the user and system interrogations; 4. variables which represent the state of the PACS and the facts.
5.1.1. Heuristic rules The set of heuristic rules contains rules for possible problems in the archiving software, retrieval software, etc. These rules result from past experience with the PACS in routine work. An example of such a rule is: IF THEN
there is an image over¯ow in the ®rst image directory and the norm process is not started start the norm process.
The rules are collected into groups, and the dierent groups are used to check the dierent parts of the PACS. There are groups that include specialized rules for software tests, hardware tests, network process tests, and so on. Another example of a heuristic rule in the OPERAS system is: IF
it is possible to transfer images from other CT scanners THEN initialize the network process at the scanner.
There are two kinds of rules. One kind involves passive rules, which analyse the state of PACS; the others are active rules, which give advice to the user or inter-
5.1.2. Meta-rules The meta-rules select the other rules. With the aid of the meta-rules, OPERAS activates specialized rules in the set of rules to check the system, and to eliminate the trouble. Depending on the initial information (e.g. no CT scanner can transfer images to the archive, but messages about already archived examinations are still being sent back from the archive), the meta-rules select dierent tests such as, for example, an archive network test, an image directory test, etc. An example of such a rule is: IF
it is not possible to transfer images from any CT-scanners and if messages are sent back from the archive process THENcheck the archive network process and the ®rst image box. Starting from the facts about the malfunction, the meta-rules enable a depth-®rst search. 5.1.3. Dialogue and system interrogation This module allows the program to gain information about the malfunction. This is done either by opening a dialogue with the user, or by performing system checks. The system informs the user about detected facts, gives advice to the user, or informs the user about its activities. During the session OPERAS automatically performs system checks. 5.1.4. Variables The state of PACS and the facts are represented by logical variables. There are mainly two kinds of variables: those that represent the state of the system, and those that represent the actual running test. Variables of the ®rst kind are, for example: a process (which performs a speci®c task) has been started, a network process has been initialised, a device is full, etc. Variables of the second kind can be: a software test is running, an archive check is running, etc. These variables, which take values of either true or false, are examined by the rules. If a variable satis®es the condition part of a rule this rule is activated, and generally one or more variables are changed. 5.2. Rule-selection strategy Dierent rule-selection strategies are implemented in the program. A meta-rule can be activated only once
M. Wiltgen / Engineering Applications of Arti®cial Intelligence 11 (1998) 469±475
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Fig. 3. Part of the OPERAS decision tree. This part shows several steps to localize possible malfunctions during the image transfer from a CTscanner to the image archive. The images of an examination are transferred over the network, stored temporarily on an image directory (CTBOX), then converted into an appropriate format (by the Norm process) and copied to the optical disk. The archive process sends a message about the successfully stored examination, back to the console of the CT-scanner.
during a session. The dierent groups of heuristic rules are selected by context restriction. Within some groups, the sequence in which a rule appears plays an important role, while in other groups the rules with the smallest number of conditions in the condition part are activated ®rst.
5.3. OPERAS session When problems occur during the operation of the PACS (for example; it is not possible to send images from a CT scanner to the optical archive), the radiographer consults the OPERAS program.
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OPERAS can be started by the radiographer via special software, the PACS-MONITOR, which is used to survey and manage the PACS. When OPERAS is started, the user ®rst selects from a menu the function (archiving, retrieving, image transfer, etc.), which is not working. (In the example above the menu item ``archiving'' is selected). Then OPERAS collects preliminary information about the state of the PACS by opening a dialogue with the user and doing system checks (see Fig. 4). OPERAS gains information by asking the user, for example: ``Is it possible to send images to the archive from the other CT-scanners? Are messages being sent back from the archive?'' According to this information, one or more metarules are activated, a hypothesis regarding the possible reason for the malfunction is set up, and a group of object rules is selected to detect and eliminate the malfunction. So a backward chaining is possible, and the trouble can be identi®ed and eliminated in a few steps. For example: on the basis of the facts that messages are sent back from the optical archive but that no CTscanner can transfer images, the network process of the archive and the temporary image directory are checked. If there is an image over¯ow in the image directory, then a check is run to see if the next process in the sequence is running, and so on. Either the program gives the user advice on how to eliminate the trouble, or the problem is eliminated automatically by the program (processes are started, etc.). At any moment during the session the user can
Fig. 4. Sequence of an OPERAS session. On starting, OPERAS gains information about the current state of the PACS by opening a dialogue with the user, analyzing the situation via condition±action rules, and ®nally either giving advice to the user or eliminating the trouble automatically.
get help, explanations and intermediate results from OPERAS. At the end of the session it is possible to get an analysis of all the activated meta-rules and object rules. An inexperienced user can get help before the beginning of the session. OPERAS explains how it interacts with the user and the PACS, and gives an example of a session. 6. Conclusion At the moment, the operation of OPERAS is restricted to the older parts of the PACS, which were originally partially developed in-house. For these components of PACS, the use of OPERAS in routine operation has been studied. As a conclusion, it can be said that OPERAS makes the routine operation less dependent on an EDP-expert, who cannot be present in the radiological department 24 h a day. It provides an easy-to-handle tool, which helps a PACS user (who is generally not a computer expert) to localize and eliminate problems during routine work. At the moment, OPERAS contains 79 rules (65 heuristic rules and 14 meta-rules) to handle dierent kinds of trouble. The rules result from past experience with the PACS in routine operation: archiving of images, retrieval of images, image transfer to the reporting consoles, and other components. The rules cover most of the problems that occur while performing these tasks. The application of the small expert system in daily routine saves time and guarantees the continuity of the work¯ow. For example: during a night shift the image transfer to the reporting console and the archive was interrupted. In the ®rst case it was then necessary to make hardcopies (for reporting) of the digital images at the CT-scanner, which was time-consuming, and the quality of the images used for reporting was inferior. In the second case all the examinations had to be archived the next day; therefore, a reorganisation of the work¯ow was necessary, and time delays occurred (due to heavier image transfers). With OPERAS, such troubles can be easily and immediately removed by the PACS user (during the night shift), and the surplus work can be avoided. The program is used mainly by radiographers. OPERAS runs on a VAX computer. It is written in Fortran, and the VAX VMS runtime library is used for the screen management and system checks. If other defects are to be taken into consideration, or if new components are to be added to the PACS, and therefore new possible sources of error introduced, the set of rules would need to be augmented. The division of the object-oriented rules into groups which are selected by the meta-rules facilitates the introduction of new rules. At the moment, the new groups must still be inserted into the source code.
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References ACR-Nema Standards Publication/no. 300, 1985. Digital Imaging and Communications. Akisada, M., Okaniwa, H., Tsuneyoshi, H., Okabe, T., 1993. Some consideration on hospital-wide PACS from the experience in Tokyo Hitachi hospital. In: H.U. Lemke, K. Inamura, C.C. Jae, Felix (Ed.). Computer Assisted Radiology. Proceedings of the International Symposium CAR93. Springer, Berlin, pp. 15±19. Giribona, P., 1991. Principles for PACS evolution. In: J. Demongeot, P. Sousa (Ed.). A ISCAMI 1: Integrated System for the Management and Manipulation of Medical Images. Springer, Paris, pp. 16±23. Greinacher, C.F.C., Bach, E.F., Herforth, M. et al, 1990. Computer assisted radiology requirements and solutions for digital diagnostic imaging. Med. Inf. 15 (1), 21±29. Meyer-Ebrecht, D., 1994. Picture archiving and communication systems (PACS) for medical application. Int. J. Biomed. Comput. 35, 91±124. Mosser, H., Urban, M., PaÈrtan, G., Hruby, W., 1994. Clinical routine operation of a ®lmless radiology department: 20 months experience. In: J. Boehme, A. Rowberg, N. Wolfman (Ed.). Computer Applications to Assist Radiology. Proceeding Book of the SCAR 94 Symposium for Computer Assisted Radiology, Winston±Salem, North Carolina, June 12±15, pp. 30±38. Wiltgen, M., Gell, G., Schneider, G.H., Gnoyke, H., 1990. PACS: Aapilot system in routine operation. Electromedica 58 (4), 124±129.
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Wiltgen, M., Gell, G., Schneider, G.H., 1991. Some software requirements for a PACS: lessons from experiences in clinical routine. Int. J. Biomed. Comput. 28, 61±70. Wiltgen, M., Gell, G., Graif, E., Stubler, S., Kainz, A., Pitzler, R., 1993. An integrated PACS-RIS in a radiological department. J. Digital Imaging 6 (1), 12±24. Wiltgen, M., Gell, G., Pitzler, R., Kainz, A., 1994. An integrated PACS-RIS: experiences and developments. In: J. Boehme, A. Rowberg, N. Wolfman (Ed.). Computer Applications to Assist Radiology. Proceeding Book of the SCAR 94 Symposium for Computer Assisted Radiology, Winston±Salem, North Carolina, June 12±15, pp. 213±218. Wiltgen, M., Gell, G., Kainz, A., Pitzler, R., Fotter, R., Graif, E., RienmuÈller, R., Sorantin, E., Ebner, F., Stollberger, R., Fuchs, D., Gnoyke, H., 1995. PACS-Graz: an early pilot project for picture archiving and communication. In: H. Hutten (Ed.). Science and Technology for Medicine: Biomedical Engineering in Graz. Pabst Science Publishers, pp. 339±363. Dr Marco Wiltgen was born in Ettelbruck in Luxemburg. After completing grammer school, he moved to Graz in Austria, where he graduated in Physics at the Karl Franz University of Graz. He received his PhD for the thesis entitled `` < CC> in the Schwinger model with Wilson and naive fermions''.Dr Wiltgen is currently employed as an analyst at the Institute of Medical Informatics, Statistics and Documentation of the Karl Franz University of Graz, where he is working in the ®eld of PACS (picture archiving and communication systems) and medical image processing, and as a lecturer at the Technical University of Graz.
Engineering Applications of Arti®cial Intelligence 11 (1998) 469±475
Contributed Paper
An expert system for troubleshooting in a picture archiving and communication system M. Wiltgen * Department for Medical Informatics, Statistics and Dokumentation, University of Graz, Austria Received 1 August 1997; accepted 1 June 1998
Abstract At the Department of Radiology of the University of Graz, a picture archiving and communication systems (PACS) is used in routine operation. The operation of the PACS is an essential part of the clinical routine. Failures which occur in one part of the system may spread out, and critically impair the routine work. To allow the operation of the PACS to be independent of the permanent presence of an EDP-expert, a rule-based expert system has been developed for trouble-shooting. This expert system makes use of standard techniques, and helps the PACS user, to eliminate problems and to guarantee smooth operation. # 1998 Elsevier Science Ltd. All rights reserved. Keywords: Expert systems; Picture archiving and communication systems; Trouble-shooting
1. Introduction With the development of imaging methods such as computed tomography (CT), magnetic resonance imaging (MR), digital subtraction angiography (DSA), digital radiography (DLR) and so on, new and successful diagnostic methods have been introduced in medicine. Starting with nuclear medicine, more and more of the imaging methods have either been digitized (for example; digital radiography) or, like CT and MR, have started as digital methods from the beginning. The number of digital images has increased continuously during the last few decades. Traditionally, hardcopies on ®lm are made from the digital images, and these hardcopies are used for archiving and reporting. Then, for the end-users of the diagnostic information (such as neurosurgeons, radiotherapists etc.), the image information is available on ®lm. The disadvantages of the use of ®lm are: (1) the high expenditure on the archive space (®lm folders are ®lling up whole rooms), (2) the loss of images during their distribution within the hospital, (3) the slowness of access to the images, and (4) the loss of information * Corresponding author. Tel.: 00 43 316 385 3587; Fax: 00 43 316 385 3590; E-mail: [email protected].
that occurs when a hard copy is made from a digital image. PACS (picture archiving and communication systems) have been developed to handle the increasing number of digital images (Meyer-Ebrecht, 1994; Giribona, 1991; Greinacher et al., 1990). In a PACS, the image-acquisition systems, the archive and the digital viewing stations are interconnected in a network, and the digital images are transferred via the network (that means without making a hardcopy) from the image-acquisition modalities to digital consoles, and to the digital archive. PACS implies the digital processing, archiving, transfer, display, etc. of image data, and this should, in principle, make hardcopies on ®lm unnecessary. The hoped-for advantages of PACS over conventional methods include several aspects: 1. ®nancialÐreduced costs for ®lms, archive space and personnel; 2. archivingÐbetter availability of images; experience has shown that in conventional ®lm archives, 25± 35% of ®lms are not available when requested (because they have been lent to somebody, are misplaced, etc.); 3. communicationÐfaster image transfer and simultaneous access from multiple points;
0952-1976/98/$ - see front matter # 1998 Elsevier Science Ltd. All rights reserved. PII: S 0 9 5 2 - 1 9 7 6 ( 9 8 ) 0 0 0 3 5 - 9
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M. Wiltgen / Engineering Applications of Arti®cial Intelligence 11 (1998) 469±475
4. interpretationÐthe image-processing capabilities of a PACS workstation, such as windowing, ®ltering, three-dimensional visualisation, quanti®cation, etc. might be an aid to diagnosis, because all the information in the images can be exploited. In a PACS, there is no longer a dependence on the locality of information, and simultaneous access to the images is possible from peripheral departments. The ®nal goal of PACS would be a completely ®lmless hospital (Akisada et al., 1993; Mosser et al., 1994). At the Department of Radiology of the University of Graz, a PACS runs as part of the daily routine (Wiltgen et al., 1993; Wiltgen et al., 1994). The PACS was integrated into the radiological department in cooperation with Siemens Erlangen, and its operation in routine work has been studied for a period of several years (Wiltgen et al., 1990). As a result of this experience, software has been developed to improve the handling and operation of the PACS. Since 1993, the PACS has been expanded by adding components based on the Siemens SIENET concept.
2. PACS con®guration The PACS in the Department of Radiology currently incorporates four CT-scanners, two MRI-scanners, one DSA, one DLR and one Ultrafast CT as modalities (see Fig. 1). In addition, it includes a radiography planning system, two reconstruction consoles, and several reporting and viewing consoles. Two archive units (320 GB online) with a total of three jukeboxes for optical disks (WORM) and another archive (52 GB online), mainly used for DLR images, serve as the long-term archive. The network is based on FDDI and Ethernet. The PACS consists partially of a Siemens SIENET PACS, with several components supplied by IMAGE DEVICE (located in the pedriatic radiology department), and, on the other hand, several components of the older PACS version. The SIENET modules are based on SUN SPARCstations, whereas the older parts are located on VAX systems. The PACS is connected with a radiological information system (RIS), so that the management of the image
Fig. 1. The PACS-con®guration at the Department of Radiology of the University of Graz. The con®guration connects several CT- and MRIscanners, a DSA and a DLR. The images produced are displayed on reporting consoles (MagicView), viewing consoles (PV) and special reconstruction consoles (GammaPlan). Dierent parts of the PACS con®guration (from dierent manufactures) are interconnected by gateways (HMG, Magic Link, ISI gateway, SPI spooler). Archive units (ISA) with jukboxes serve as an image store. The network is based on FDDI and Ethernet.
M. Wiltgen / Engineering Applications of Arti®cial Intelligence 11 (1998) 469±475
archive is done by the RIS, using patient data to select and retrieve the images. All the images produced from CT, MRI, UltrafastCT, DSA and DLR are routinely stored in the optical archives. The PACS is used for dierent tasks including archiving, retrieval of previous examinations, reporting of selected examinations on the digital reporting consoles, and image distribution to selected places within the hospital. 3. PACS software process structure The PACS is organized as a group of independent software processes, which communicate with each other. These processes run in the background, and provide access to the images and image data. The processes execute tasks such as: transferring images over the network (by the network process), conversion of images (by the norm process), submissions into databases, etc. The process structure is distributed over several computers. First, the processes are in a waiting state, and must be activated by a command from another process. The processes work simultaneously, and the sequence of processes operates as a pipeline; while the last images of an examination are still being transferred over the network, the ®rst images have already been submitted into the image database. The communication between the processes is administrated by the Siemens PACSNET/SPI toolkit, which complies with the ACR-Nema commands to request and transfer images (ACR-Nema, 1985). 4. Problem description A PACS plays an important role in organising the tasks of a radiological department, deeply in¯uencing the organisation and the infrastructure. The PACS is not stand alone equipment which runs independently from other equipment. Because many dierent components of the radiology department are interconnected in the network, failures that occur in one part of the PACS may spread out and hamper other, routine work (Wiltgen et al., 1991). Such failures can include both software and hardware failures, although a high proportion of them are software failures. Therefore, in this paper, the attention is mainly concentrated on this kind of problem. Some examples of such failures are: a software process is not active, the communication between two processes is interrupted, a device is full, etc. Then tasks performed by the PACS, such as archiving or image transfer, are impaired. If problems of this sort are not eliminated after a certain time, then extensive delays in the routine work may occur, or the routine may even become comple-
471
tely blocked. The PACS runs 24 h a day. Especially during the night and weekend shifts, when no system manager is present to localize and eliminate malfunctions, the routine work would be critically in¯uenced and impaired. Therefore, at least during the night and weekend shifts, it is important that malfunctions of the system can be eliminated by the users themselves. The PACS in Graz was one of the earliest pilot projects, and one of the ®rst systems running as routine (Wiltgen et al., 1995). From the beginning of the project it was of special importance to gain experience about the introduction of the PACS in a radiological department: how the work¯ow could be optimised, and which requirements were needed to guarantee a smooth operation. Experience with the routine operation of the PACS shows that most of the problems that occur can be localised and removed by the application of a de®ned set of rules. From the point of view of the radiographers, one of the requirements was that it should be possible for them to check out and handle the PACS, especially if malfunctions were to occur, and to obtain information about the state of the system. Therefore, a computer program has been developed to help the PACS user (who is generally not a computer expert) to easily localize and eliminate malfunctions during routine operation.
5. Troubleshooting with an expert system OPERAS (operating assistant) is a rule-based expert system for error detection and elimination in the PACS. It is an intelligent tool to provide PACS user support, and allows the user to recover the normal operating state of the PACS. This expert system makes the routine operation as independent as possible of the presence of an electronic data-processing expert. When the user consults the OPERAS program, OPERAS ®rst opens a dialogue with the user to gain information about the state of the PACS. Then the facts are analysed by condition±action rules, a hypothesis about the possible reason of the malfunction is formulated and either advice is given to the user on how to eliminate the problem, or the malfunction is eliminated automatically by the program. 5.1. OPERAS components The OPERAS program is based on condition±action rules. The knowledge base, covering the reasons for possible malfunctions, and how to eliminate them, is represented by heuristic rules. OPERAS consists of four main components (see Fig. 2): 1. a set of heuristic rules (object rules) for the localisation and elimination of malfunctions;
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act with the system. A rule of the ®rst kind can, for example, check whether a software process has started, or if there is an over¯ow in an image directory. A rule of the second kind can start the software process, etc. A part of the decision tree is shown in Fig. 3.
Fig. 2. Overview of the OPERAS components. The system consists of four main components: (i) a set of heuristic rules to localise and eliminate malfunctions during the routine work; (ii) a set of metarules for the selection of specialized groups of heuristic rules to check dierent components of the PACS; (iii) modules for the user dialogue and system checks; and (iv) variables that represent the actual state of the PACS.
2. meta-rules for the selection of tests; 3. modules for the dialogue with the user and system interrogations; 4. variables which represent the state of the PACS and the facts.
5.1.1. Heuristic rules The set of heuristic rules contains rules for possible problems in the archiving software, retrieval software, etc. These rules result from past experience with the PACS in routine work. An example of such a rule is: IF THEN
there is an image over¯ow in the ®rst image directory and the norm process is not started start the norm process.
The rules are collected into groups, and the dierent groups are used to check the dierent parts of the PACS. There are groups that include specialized rules for software tests, hardware tests, network process tests, and so on. Another example of a heuristic rule in the OPERAS system is: IF
it is possible to transfer images from other CT scanners THEN initialize the network process at the scanner.
There are two kinds of rules. One kind involves passive rules, which analyse the state of PACS; the others are active rules, which give advice to the user or inter-
5.1.2. Meta-rules The meta-rules select the other rules. With the aid of the meta-rules, OPERAS activates specialized rules in the set of rules to check the system, and to eliminate the trouble. Depending on the initial information (e.g. no CT scanner can transfer images to the archive, but messages about already archived examinations are still being sent back from the archive), the meta-rules select dierent tests such as, for example, an archive network test, an image directory test, etc. An example of such a rule is: IF
it is not possible to transfer images from any CT-scanners and if messages are sent back from the archive process THENcheck the archive network process and the ®rst image box. Starting from the facts about the malfunction, the meta-rules enable a depth-®rst search. 5.1.3. Dialogue and system interrogation This module allows the program to gain information about the malfunction. This is done either by opening a dialogue with the user, or by performing system checks. The system informs the user about detected facts, gives advice to the user, or informs the user about its activities. During the session OPERAS automatically performs system checks. 5.1.4. Variables The state of PACS and the facts are represented by logical variables. There are mainly two kinds of variables: those that represent the state of the system, and those that represent the actual running test. Variables of the ®rst kind are, for example: a process (which performs a speci®c task) has been started, a network process has been initialised, a device is full, etc. Variables of the second kind can be: a software test is running, an archive check is running, etc. These variables, which take values of either true or false, are examined by the rules. If a variable satis®es the condition part of a rule this rule is activated, and generally one or more variables are changed. 5.2. Rule-selection strategy Dierent rule-selection strategies are implemented in the program. A meta-rule can be activated only once
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Fig. 3. Part of the OPERAS decision tree. This part shows several steps to localize possible malfunctions during the image transfer from a CTscanner to the image archive. The images of an examination are transferred over the network, stored temporarily on an image directory (CTBOX), then converted into an appropriate format (by the Norm process) and copied to the optical disk. The archive process sends a message about the successfully stored examination, back to the console of the CT-scanner.
during a session. The dierent groups of heuristic rules are selected by context restriction. Within some groups, the sequence in which a rule appears plays an important role, while in other groups the rules with the smallest number of conditions in the condition part are activated ®rst.
5.3. OPERAS session When problems occur during the operation of the PACS (for example; it is not possible to send images from a CT scanner to the optical archive), the radiographer consults the OPERAS program.
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OPERAS can be started by the radiographer via special software, the PACS-MONITOR, which is used to survey and manage the PACS. When OPERAS is started, the user ®rst selects from a menu the function (archiving, retrieving, image transfer, etc.), which is not working. (In the example above the menu item ``archiving'' is selected). Then OPERAS collects preliminary information about the state of the PACS by opening a dialogue with the user and doing system checks (see Fig. 4). OPERAS gains information by asking the user, for example: ``Is it possible to send images to the archive from the other CT-scanners? Are messages being sent back from the archive?'' According to this information, one or more metarules are activated, a hypothesis regarding the possible reason for the malfunction is set up, and a group of object rules is selected to detect and eliminate the malfunction. So a backward chaining is possible, and the trouble can be identi®ed and eliminated in a few steps. For example: on the basis of the facts that messages are sent back from the optical archive but that no CTscanner can transfer images, the network process of the archive and the temporary image directory are checked. If there is an image over¯ow in the image directory, then a check is run to see if the next process in the sequence is running, and so on. Either the program gives the user advice on how to eliminate the trouble, or the problem is eliminated automatically by the program (processes are started, etc.). At any moment during the session the user can
Fig. 4. Sequence of an OPERAS session. On starting, OPERAS gains information about the current state of the PACS by opening a dialogue with the user, analyzing the situation via condition±action rules, and ®nally either giving advice to the user or eliminating the trouble automatically.
get help, explanations and intermediate results from OPERAS. At the end of the session it is possible to get an analysis of all the activated meta-rules and object rules. An inexperienced user can get help before the beginning of the session. OPERAS explains how it interacts with the user and the PACS, and gives an example of a session. 6. Conclusion At the moment, the operation of OPERAS is restricted to the older parts of the PACS, which were originally partially developed in-house. For these components of PACS, the use of OPERAS in routine operation has been studied. As a conclusion, it can be said that OPERAS makes the routine operation less dependent on an EDP-expert, who cannot be present in the radiological department 24 h a day. It provides an easy-to-handle tool, which helps a PACS user (who is generally not a computer expert) to localize and eliminate problems during routine work. At the moment, OPERAS contains 79 rules (65 heuristic rules and 14 meta-rules) to handle dierent kinds of trouble. The rules result from past experience with the PACS in routine operation: archiving of images, retrieval of images, image transfer to the reporting consoles, and other components. The rules cover most of the problems that occur while performing these tasks. The application of the small expert system in daily routine saves time and guarantees the continuity of the work¯ow. For example: during a night shift the image transfer to the reporting console and the archive was interrupted. In the ®rst case it was then necessary to make hardcopies (for reporting) of the digital images at the CT-scanner, which was time-consuming, and the quality of the images used for reporting was inferior. In the second case all the examinations had to be archived the next day; therefore, a reorganisation of the work¯ow was necessary, and time delays occurred (due to heavier image transfers). With OPERAS, such troubles can be easily and immediately removed by the PACS user (during the night shift), and the surplus work can be avoided. The program is used mainly by radiographers. OPERAS runs on a VAX computer. It is written in Fortran, and the VAX VMS runtime library is used for the screen management and system checks. If other defects are to be taken into consideration, or if new components are to be added to the PACS, and therefore new possible sources of error introduced, the set of rules would need to be augmented. The division of the object-oriented rules into groups which are selected by the meta-rules facilitates the introduction of new rules. At the moment, the new groups must still be inserted into the source code.
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Wiltgen, M., Gell, G., Schneider, G.H., 1991. Some software requirements for a PACS: lessons from experiences in clinical routine. Int. J. Biomed. Comput. 28, 61±70. Wiltgen, M., Gell, G., Graif, E., Stubler, S., Kainz, A., Pitzler, R., 1993. An integrated PACS-RIS in a radiological department. J. Digital Imaging 6 (1), 12±24. Wiltgen, M., Gell, G., Pitzler, R., Kainz, A., 1994. An integrated PACS-RIS: experiences and developments. In: J. Boehme, A. Rowberg, N. Wolfman (Ed.). Computer Applications to Assist Radiology. Proceeding Book of the SCAR 94 Symposium for Computer Assisted Radiology, Winston±Salem, North Carolina, June 12±15, pp. 213±218. Wiltgen, M., Gell, G., Kainz, A., Pitzler, R., Fotter, R., Graif, E., RienmuÈller, R., Sorantin, E., Ebner, F., Stollberger, R., Fuchs, D., Gnoyke, H., 1995. PACS-Graz: an early pilot project for picture archiving and communication. In: H. Hutten (Ed.). Science and Technology for Medicine: Biomedical Engineering in Graz. Pabst Science Publishers, pp. 339±363. Dr Marco Wiltgen was born in Ettelbruck in Luxemburg. After completing grammer school, he moved to Graz in Austria, where he graduated in Physics at the Karl Franz University of Graz. He received his PhD for the thesis entitled `` < CC> in the Schwinger model with Wilson and naive fermions''.Dr Wiltgen is currently employed as an analyst at the Institute of Medical Informatics, Statistics and Documentation of the Karl Franz University of Graz, where he is working in the ®eld of PACS (picture archiving and communication systems) and medical image processing, and as a lecturer at the Technical University of Graz.