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At least 19 recordsLinked to original sources

PubMed2001

Designing fault-tolerant distributed archives for picture archiving and communication systems.

PURPOSE: Distributed archives in a picture archiving and communication system (PACS) environment can provide added fault tolerance and fail-over capability, as well as increased load capacity at a more economical price than traditional 'high-availability" systems. Systems can be configured with varying levels of fault tolerance, depending on the amount of redundancy desired. There is, however, a direct correlation between the level of hardware redundancy and cost to implement. This presentation details the system design for fault-tolerant distributed archives as well as several options for redundancy, referencing implementation of a fault-tolerant archive system at the University of Utah. METHODS: The distributed archive system described here is based on Image Devices' image archive software, which can be implemented on multiple individual archive servers in order to distribute archive functionality and operational load. The configuration and implementation of the individual servers together make up the distributed archive system and does not impact the ability of the system to be scaled to meet future requirements. Several implementation and configuration options exist, including the ability for servers to maintain replicated databases containing patient and image information. Thus, each archive can be aware of all information and the location of this information within the distributed archive system. RESULTS: The goal is to produce systems that will still be operational in the event of any single point of failure, ie, a network connection failure between facilities or the failure of a single archive server within the distributed system. During normal operation, workload for image acquisition, image routing and image query requests will be distributed between the archive servers. If the system is deployed in a multifacility environment, each archive server can be configured to be responsible for the acquisition and image distribution management within that server's local facility. If the system is deployed in a single facility environment, load can be distributed evenly between the archive servers based on an understanding of the workload requirements generated be each acquisition and display device in the system. In the event that an archive server fails, other archive servers within the system will have the ability to provide some or all of the failed server's functionality. The degree of fail-over capability is dependent on the archive server's configuration as well as hardware redundancy employed. Three levels of fault-tolerant design can be achieved with this system architecture: (1) duplicate work capability only; (2) duplicate work capability and short-term image cache; (3) duplicate work capability, short-term image cache, and longterm image archival. Using the basic fault-tolerant design above, we have implemented a multifacility distributed archive system at the University of Utah. This system was implemented at a fraction of the cost of true "high-availability" archive architectures yet provides constant up time for the PACS system. If the network connection between the two locations goes down, each site is still fully functional for soft-copy read, as well as image acquisition and distribution. If either of the archive servers goes down, the image sources are redirected to the other archive server. The operational server then handles image distribution for both locations. Access to images in the short-term image cache is available to both archive servers and is not affected by loss of the network connection or remote server. Because there is ony one long-term archive device, the ability to retrieve images from long-term storage is the only function compromised by a network or server failure. CONCLUSION: By implementing distributed archives in a PACS environment, it is possible to achieve a highly fault-tolerant system without the expense of high-availability hardware and software. The design concepts outlined here can be applied to any PACS system that supports distributed archive functionality.

Computer Systems↗

PubMed1999

The strategic and operational characteristics of a distributed phased archive for a multivendor incremental implementation of picture archiving and communications systems.

The long-term (10 years) multimodality distributed phased archive for the Medical Information, Communication and Archive System (MICAS) is being implemented in three phases. The selection process took approximately 10 months. Based on the mandatory archive attributes and desirable features, Cemax-Icon (Fremont, CA) was selected as the vendor. The archive provides for an open-solution allowing incorporation of leading edge, "best of breed" hardware and software and provides maximum flexibility and automation of workflow both within and outside of radiology. The solution selected is media-independent, provides expandable storage capacity, and will provide redundancy and fault tolerance in phase II at minimum cost. Other attributes of the archive include scalable archive strategy, virtual image database with global query, and an object-oriented database. The archive is seamlessly integrated with the radiology information system (RIS) and provides automated fetching and routing, automated study reconciliation using modality worklist manager, clinical reports available at any Digital Imaging and Communications in Medicine (DICOM) workstation, and studies available for interpretation whether validated or not. Within 24 hours after a new study is acquired, four copies will reside within different components of the archive including a copy that can be stored off-site. Phase II of the archive will be installed during 1999 and will include a second Cemax-Icon archive and database using archive manager (AM) Version 4.0 in a second computer room.

Computer Communication Networks↗

PubMed2001

Management of the picture archiving and communications system archive at Texas Children's Hospital.

As hospitals convert from conventional film-based imaging to picture archival and communications systems (PACS), methods for managing an enormous library of images must change considerably. While most hospitals are required to retain general, nonmammographic, radiologic images for 7 years beyond the examination date, our pediatric hospital must maintain images until the child's eighteenth birthday, plus the 5-year statute of limitations. Although the physical extent of an electronic archive is tiny compared with a film archive, a long-range strategy is required to ensure that electronic images acquired today can be retrieved and viewed 23 years in the future. Challenges to the long-term stability of the electronic archive include the limited and uncertain shelf life of high-density electronic storage media, the finite maintainability of the electromechanical systems for reading the media, the short product lifetime of software for accessing the images, rapid development of higher density storage products, and the exponential advancement of computer and networking technology that fuels product obsolescence. Since we cannot assure the function of our current archive in two decades, we are committed to a continual process of migration of old electronic image data to newer media and systems. As an early-adopter of PACS technology, Texas Children's Hospital's (TCH) archive management experience is relevant to others. Although not filled to capacity, our first digital archive, based on phase-change write-once-read-many (WORM) technology, was forced into an inactive status by software and hardware changes. Our second set of archives was partially filled with low-density magneto-optical disk (MOD) media, when the drives were upgraded to high density and then filled to capacity. This undesirable situation forced us into shelf management of media. Our third-generation archive is based on a helical tape library with the capacity to contain 7 years of examinations. We will describe the motivation for data migration, limitations in the methods available to perform the migration, and unanticipated benefits of the migration process.

Computer Communication Networks↗

PubMed1995

Data clustering and other archive retrieval strategies for teleradiology and picture archiving and communication systems.

A key advantage in the conversion from film-based to digital radiology is the possibility of a long-term on line electronic archival of patient studies. The popular approach based on optical disk jukeboxes for the long-term archive and magnetic disk storage for data caching is not economically attractive because of the cost of both the jukebox and the medium. Strategies for extending the archival system design with a tape jukebox have been studied. The proposed strategy calls for the use of high-ratio lossy compression together with low-cost tape storage to make long-term on line archiving more affordable. An intelligent prefetching algorithm based on hospital information system and radiologic information system triggers, which in turn are augmented by manual case preparation, can effectively overcome the longer latency of ad hoc retrievals. This longer latency is caused by both system-level bottlenecks and the sequential access constraint of the tape drive. Strategies for image clustering and tape allocation by patient classification also enhance retrieval efficiency. This archival design using image compression, prefetching, and clustering could be implemented in many of the existing teleradiology and picture archiving and communication systems.

Algorithms↗

PubMed1995

From archives to picture archiving and communications systems.

Keeping organised and consistent film archives is a well-known problem in the radiological world. With the introduction of digital modalities (CT, MR,...) the idea of archiving the image data in a non common way was born. The aim is to keep the information in digital form from acquisition to destination, e.g. archives, viewing station, teleradiology, a task that was not as easy as some people believed, due to bare technical possibilities and to the lack of standards concerning medical image data. These reasons made it not so common to integrate components of different origins into a digital Picture Archiving and Communication environment. How should we attempt to integrate the analogue examinations? It is ridiculous to exclude the conventional XR-examination that accounts for more than 70% of the total production. We believe that there will be a migration to light-stimulable phosphor plates, but these are not yet user friendly and certainly not cost effective. We have similar problems of immature technology as we had for the digital modalities. In a first attempt the bridge can be crossed, between the two worlds by means of converters (laser scanner, CCD camera). PACS will become a reality in the future as almost all examinations will be digitalized. We are now in a transition period with its inconveniences, but we will gain a lot soon. The migration from piles of films through a computer assisted radiological archiving system to a full digital environment is sketched in a historical survey.

Radiology↗

PubMed1994