Albert W. K. Wong

Implementation of a large-scale picture archiving and communication system

This paper describes the implementation of a large-scale picture archiving and communication system (PACS) in a clinical environment. The system consists of a PACS infrastructure, composed of a PACS controller, a database management system, communication networks, and optical disk archive. It connects to three MR units, four CT scanners, three computed radiography systems, and two laser film digitizers. Seven display stations are on line 24 h/day, 7 days/wk in genitourinary radiology (2K), pediatric radiology in-patient (1K and 2K) and outpatient (2K), neuroradiology (2K), pediatric ICU (1K), coronary care unit (1K), and one laser film printing station. The PACS is integrated with the hospital information system and the radiology information system. The system has been in operation since February 1992. We have integrated this PACS as a clinical component in daily radiology practice. It archives an average of 2.0-gigabyte image data per workday. A 3-mo system performance of various components are tabulated. The deployment of this large-scale PACS signifies a milestone in our PACS research and development effort. Radiologists, fellows, residents, and clinicians use it for case review, conferences, and occasionally for primary diagnosis. With this large-scale PACS in place, it will allow us to investigate the two critical issues raised when PACS research first started 10 yrs ago: system performance and cost effectiveness between a digital-based and a film-based system.

Multimedia in the radiology environment: current concept.

Multimedia has different meanings according to its context. Here, multimedia in the radiology environment is defined as the integration of multiple radiology and medical information systems to facilitate the practice of radiology. These information systems include the hospital information system, radiology information system, picture archiving and communication systems, voice reporting, library information systems, and electronic mail and file systems. The concept of multimedia within the context of integration of these database systems will be presented. An example is given on how to access these information systems by a radiologists desktop personal computer.

Clinical experience with a second-generation hospital-integrated picture archiving and communication system

In a previous report we described a second-generation hospital-integrated picture archiving and communication system (HI-PACS) developed in-house. This HI-PACS had four unique features not found in other PAC systems. In this report, we will share some of our clinical experiences pertaining to these features during the past 12 months. We first describe the usage characteristics of two 2,000-line workstations (WSs), one in the in-patient and the second in the out-patient neuroradiology reading area. These two WSs can access neuro-images from 10 computed tomographic and magnetic resonance scanners located at two medical centers through an asynchronous transfer mode network connection. The second unique feature of the system is an intensive care unit (ICU) server, which supports three WSs in the pediatric, medical surgery, and cardiac ICUs. The users’ experiences and requests for refinement of the WSs are given. Another feature is physician desk-top access of PACS data. The HI-PACS provides a server connected to more than 100 Macintosh users for direct access of PACS data from their offices. The server’s performance and user critiques are described. The last feature is a digital imaging and communication in medicine (DICOM) connection of the HI-PACS to a manufacturer’s ultrasound PACS module. The authors then outline the interfacing process and summarize some of the difficulties encountered. Developing an in-house PACS has many advantages but also some drawbacks. Based on experience, the authors have formulated three axioms as a guide for in-house PACS development.

Performance characteristics of an ultrafast network for PACS

Three difficult problems in making picture archiving and communication systems (PACS) a clinical reality in radiology are image archiving, very high-resolution display stations, and high-speed networking. This paper considers high-speed image transmission through a high- capacity network. Several commercially available high-speed networks were tested over the past year. Only one of these networks (UltraNet) has adequate throughput and capacity potential necessary for the PACS used in the test. The focus of this experiment is to determine the throughput and capacity characteristics of this star topology networking scheme as relates to the operation of a PACS in the clinical environment. A large-scale test was performed to gauge network memory-to-memory performance for three networking configurations modeling those in a PACS: duplex, parallel and relay. Ten computers used in the PACS (Sun 3 and 4 class computers) were connected with UltraNet for the test. For point-to-point throughput (half-duplex model) the network delivers up to 3.1 megabytes/second (MBps) for Sun 3/computers and 4.7 MBps for the Sun SparcServer 490. As regards capacity considerations (parallel model), five parallel image transfer processes generated a maximum of 13.9 MBps through the network. Only a slight degradation in individual process throughput was observed (1.4%). With regard to shared access to high-contention resources on the PACS network (e.g., archive servers), this network demonstrated equal sharing of server networking capacity between various client computers (relay model). For disk-to-disk performance measurement under loaded clinical conditions between two SparcServer 490s, the overall average transfer rate was found to be 1.125 +/- 0.257 MBps, while the average network transfer rate of 3.632 +/- 1.542 MBps was determined. This compares to an average overall transfer rate of 0.389 +/- 0.061 MBps and average network transfer rate under similar conditions of 0.568 +/- 0.060 MBps using Ethernet. For disk-to-memory transfer from a parallel transfer disk (PTD) on a Sun 4/470 to the 2K display frame buffer on a Sun 4/370, the PTD portion of the transfer required 1.2 seconds (6.7 MBps) and the network portion required 1.04 seconds (7.7 MBps) for an overall transfer rate of 3.6 MBps.

Implementation of a digital archive center for a radiology department

A distributed digital archive system configured with dual archive devices (two archive servers, two database servers and two 680-Gbyte optical libraries) that provides fault-tolerant image archival has been implemented for the Radiology Department at UCLA. Digital images from various radiologic imaging devices are transmitted via Ethernet and FDDI networks to archive servers, where images are archived to optical disks and distributed to remote display stations or the print station via 1-Gbit/sec high-speed UltraNet network. The dual configuration of the system provides non-interrupt archive operations in the event of failure of any of the archive components. Once a failed device is detected, the system automatically re-configures itself so that all images are routed to the second equivalent device and archived. The global Ethernet network serves as a backup for the FDDI and UltraNet networks. In the even of FDDI or UltraNet failure, all images can be transmitted across the Ethernet. The system archives 1.5 to 2.0 Gbytes of data per day and provides inter-sectional image referencing throughout the department.© (1992) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Performance of asynchronous transfer mode (ATM)local area and wide area networks for medical imaging transmission in clinical environment

Asynchronous transfer mode (ATM) technology emerges as a leading candidate for medical image transmission in both local area network (LAN) and wide area network (WAN) applications. This paper describes the performance of an ATM LAN and WAN network at the University of California, San Francisco. The measurements were obtained using an intensive care unit (ICU) server connecting to four image workstations (WS) at four different locations of a hospital-integrated picture archiving and communication system (HI-PACS) in a daily regular clinical environment. Four types of performance were evaluated: magnetic disk-to-disk, disk-to-redundant array of inexpensive disks (RAID), RAID-to-memory, and memory-to-memory. Results demonstrate that the transmission rate between two workstations can reach 5-6 Mbytes/s from RAID-to-memory, and 8-10 Mbytes/s from memory-to-memory. When the server has to send images to all four workstations simultaneously, the transmission rate to each WS is about 4 Mbytes/s. Both situations are adequate for radiologic image communications for picture archiving and communication systems (PACS) and teleradiology applications.

Subsystem Throughputs of a Clinical Picture Archiving and Communications System

We measured the throughtput rates of individual picture archiving and communications system (PACS) subsystems including the acquisition, archive, display, and communication network as a basis of evaluation the overall throughput of our clinical PACS. The throughput rate of each PACS subsystem was measured in terms of average residence time of individual images in the subsystem. The residence time of an image in a PACS subsystem was determined by the total time the image was required to be processed within the subsystem. The overall throughput of the PACS was measured as the total residence time of an image in the various subsystems. We also measured throughputs of the PACS subsystems using three types of networks (Ethernet; fiber distributed data interface; and UltraNet, UltraNetwork Technologies, San Jose, CA), and the results were compared. Approximately 200 gigabytes of data transactions including magnetic resonance, computed tomography and computed radiography images from our PACS were analyzed. Results showed that PACS throughput was limited by three major factors: (1) low-speed data interface used in the radiologic imaging devices and archive devices; (2) competition for systems processing time among the PACS processes; and (3) network degradation caused by heavy network traffic. We concluded that PACS performance could be improved with a well-designed network architecture, a job prioritizing mechanism, and an image routing strategy. However, device-dependent low-speed data interface has limited PACS performance.

Use of personal computer technology in supporting a radiological review workstation

Recent advances in personal computer technology have made these low-cost platforms quite attractive for the implementation of radiological workstations, particularly in those cases where high throughput is not critical (such as clinical review workstations). In light of this observation, the objectives of this on-going project are threefold: (1) to identify the characteristics and performance specifications that are desirable in a radiological review workstation (within the UCSF PACS architecture), (2) to review current personal computer technology in terms of its ability to support such a workstation, and (3) to design and implement a prototype hardware and software architecture. This paper outlines our progress to data and discusses some of our projections for the near future.

Second generation picture archiving and communication systems

A modern radiology department utilizes multimedia technologies to facilitate its operation. Multimedia technologies include hardware platform, information systems, databases, communication protocols, display technology and system interface and integration. Current existing PACS can not handle this multimedia information because of its closed architectural design. This paper describes the concept of second generation PACS and its design and implementation at the University of California, San Francisco. The second generation PACS concept consists of four major components: folder manager, platter manager, image and data format standardization, and integration of heterogeneous information systems.

Hierarchical image storage management: design and implementation for a distributed PACS

Existing picture archiving and communication systems (PACS) lack intelligence in managing radiologic images distributed throughout individual PACS components (i.e. the acquisition, archive, and display subsystems), resulting in inefficient access to images. A multi-level storage system within our departmental PACS has been developed which minimizes access time for both current and historical images. The storage management system is based on a composite staging mechanism utilizing multiple storage media: redundant array of inexpensive disks (RAID), magnetic disks, erasable magneto-optical disks, and write-once-read-many (WORM) optical disks. Three levels of access to images at display stations are provided: (1) immediate access to both current and selected historical images via local RAID disks, (2) fast retrieval of images from archive subsystems cache magnetic disks, and (3) retrieval of any historical images from long-term archives magneto-optical disks and WORM disks. Mechanisms implemented in the system include: image routing, image stacking, image aging, HIS/RIS/PACS interfacing, image pre-fetching, studies grouping, and platter management. The storage management system for our distributed PACS was evaluated in terms of image access time at the display stations. With its multi-level storage architecture, the system demonstrated a 70% improvement in image access time compared with a centralized storage system. We conclude that fast access to radiologic images in PACS can be achieved through a well-designed, multi-level storage architecture.