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Biomedical subjects

B K Stewart

Publications and source records attributed to B K Stewart.

33 records · Page 2Linked to original sources
PubMed1993

Teleconferencing for cost-effective sharing of radiology educational resources: potential and technical development.

To develop a cost-effective method of sharing educational resources, a dial-up teleconferencing network was implemented between three radiologic sites for a 30-day period of evaluation. By means of standard dial-up telephone channels, compressed video and audio signals displayed radiologic images, slides, and text, allowing residents and faculty from the three sites to participate in sight and sound interactions. Each of the three sites used compressed video/audio coder-decoders (codecs) conforming to the Consultative Committee on International Telegraphy and Telephony H.261 standard. Four video cameras were used at each site, and the audio was run in full duplex mode. A multipoint video bridge was used to broadcast codec output signals to the input lines of the other codecs. Our evaluation found audio quality to be suboptimal, but capable of being improved; diagnostic image quality was adequate when a video zoom mode was used; the digital-archive mode of the codec proved advantageous; the H.261 codec permitted participation from all sites; and all conference lecturers were able to conduct their conferences as they were accustomed. Although audio quality and spatial resolution need to be improved, the results of this pilot study imply that dial-up compressed video conferencing has the potential to become a practical, cost-effective method of sharing educational resources by means of interactive radiologic multisite educational programs.

Computer Communication Networks↗
PubMed1992

Design of a high-speed, high-resolution teleradiology network.

A teleradiology system acquires radiographic images from one location and transmits them to one or more distant sites where they are displayed and/or converted to hard-copy film recordings. The long-term goal of teleradiology research is to show that teleradiology systems can provide diagnostically equivalent results when compared with conventional radiographic film interpretation. If this hypothesis is proven, provision of the following radiology services will be improved: (1) providing for primary interpretation of radiological images for patients in underserved areas as well as in other medical facilities; (2) integration of radiological services for multihospital/clinic health care provider consortiums; (3) improving emergency service and intensive care unit coverage; (4) offering consulting-at-a-distance with subspecialty radiologists; and (5) providing radiologists in the community or in rural areas with immediate access to large academic centers for help in the interpretation of difficult and problematic cases. We are designing a high-speed, high-resolution teleradiology network that will communicate between our level 3 medical center and several outlying medical centers within the metropolitan area. Computed tomography (CT), magnetic resonance (MR), and screen-film examinations will be digitized to 2,000 x 2,000 or 4,000 x 4,000 pixels at the remote sites, transmitted to the central referral facility, and sent to a laser film printer, replicating the original film. This film may then be used for primary diagnosis, overreading/consultative purposes, or for emergency department preparation. Inherently digital modality data (eg, MR and CT) can be sent without digitization of the multiformat film if desired.

Computer Communication Networks↗
PubMed1992

PACS mini refresher course. Local area network topologies, media, and routing.

Picture archiving and communication systems (PACS) use local area networks (LANs) for the transfer of images and image-related data. There are several aspects of LANs that are used to describe and categorize them: topology, the media used for transmission, and the medium access control (MAC) protocols. The four basic topologies are the bus, tree, ring, and star; the four primary types of media used for LANs include coaxial cable, twisted-pair wire, fiberoptic cables, and wireless. The wireless LANs that use infrared and radio frequencies are new but promising. Of the three MACs presently being used--Ethernet, fiber distributed data interface (FDDI), and UltraNet--Ethernet is the most common. LANs can be interconnected by means of the repeater, bridge, router, and gateway internetworking devices. The future of LAN development lies in increased standardization and increased connectivity in order to make teleradiology a reality.

Local Area Networks↗
PubMed1992

PACS mini refresher course. Wide area network strategies for teleradiology systems.

Teleradiology systems require the use of wide area networks (WANs). Design and implementation of a WAN depend on the number of images to be transmitted, desired digital image throughput (based on signaling rate), and cost of the communications link. Image transmission load must be estimated before the communications link can be selected. Communications links used in WANs include T-1 carrier point-to-point service, digital service (DS)-1 dial-up service, DS-3 point-to-point service, DS-0 dial-up service, digital microwave, fiberoptic local loop carriers, and metropolitan area networks (MANs). Depending on the distance between sites, T-1 service may be less costly than DS-1 service; however, for distances more than 200 miles, DS-1 service can be less expensive and more flexible. Both of these services and DS-0 service have lower signaling rates than DS-3 service, which is the fastest and most expensive link. Microwave and fiberoptic links are less expensive but have distance limitations of 14 and 30 miles, respectively. MANs are still being developed but hold the promise of higher signaling rates at lower costs.

Computer Communication Networks↗
PubMed1992

Performance characteristics and image fidelity of gray-scale monitors.

Gray-scale monitors are an essential element of electronic radiology, and their ability to provide images that are perceived to be identical to those available on conventional or laser-printed film is crucial to success of electronic radiology. Image fidelity is measured in physical characteristics (luminance, dynamic range, distortion, resolution, and noise) and with psychophysical techniques, including receiver operator characteristics analysis with clinical images and testing with contrast-detail patterns to determine threshold contrast. Currently, laser-printed images facilitate greater information transfer than does a gray-scale monitor because of their higher absolute luminance (500 ft-L vs 60 ft-L), greater perceived dynamic range, and better spatial resolution. In the near future, the developments of gray-scale monitors with 150-200 ft-L luminance, a display standard based on just noticeable differences, and algorithms to improve similarities between gray-scale display images and laser-printed images will help increase the acceptability of monitors as a means to make primary diagnoses.

Computer Peripherals↗
PubMed1991

Software and hardware integration of a microprogrammable state machine for NMR imaging.

We have integrated a commercially available microprogrammable state machine (Tecmag PULSkit) for use as a magnetic resonance pulse programmer. Providing the capability for active research environment imaging protocols, it features timing resolution of 100 nsec, ten 16-bit loop counters, and individually addressable look-up tables. This integration involved hardware and software integration with a VAX 11/750 at several levels. Hardware: Each of the three gradient channels employs three digital-to-analog converters (DACs). An 8-bit, 4-quadrant, multiplying DAC generates the gradient waveform shape. A 12-bit DAC generates the multiplying DAC scaling voltage, controlling gradient amplitude and sign. A third 12-bit DAC produces a gradient offset (shim) voltage. An eddy current compensation network is present for each gradient channel. Software: The software design philosophy was to create a flexible interface (interactive window environment), while not constraining complex manipulation of the hardware (direct use of the pulse-sequence compiler primitives and microprogramming). The software levels include (a) pulse-sequence microprogramming, (b) pulse-sequence compiler, (c) interactive parameter specification, and (d) canned pulse-sequence microcode library.

Computer Systems↗
PubMed1991

An ultrafast network for communication of radiologic images.

The three most 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 article considers high-speed image transmission through a high-capacity network. Our laboratory has tested several commercially available high-speed networks over the past year. Only one of these networks (UltraNet) has adequate throughput and capacity potential necessary for our PACS. The focus of this experiment is to determine the throughput and capacity characteristics of this star topology networking scheme as they relate to the operation of a PACS in the clinical environment. A large-scale test was done to gauge network performance for three networking configurations modeling those in a PACS: duplex, parallel, and relay. Ten computers used in our PACS (Sun 3 and 4 computers) were connected with UltraNet. For point-to-point throughput (half-duplex model), the network delivers up to 3.1 megabytes/sec for Sun 3 computers and 6.8 megabytes/sec for the Sun Sparcserver 490. As regards capacity considerations (parallel model), five parallel image transfer processes generated a maximum of 13.9 megabytes/sec 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 the various client computers. With the encouraging results of this experiment, we believe that the UltraNet network will be sufficient for the image communication requirements of our PACS. We are proceeding with the implementation of UltraNet as the high-speed backbone of our extended PACS network.

Computers↗
PubMed1988

Picture archiving and communication systems (PACS) for radiological images: state of the art.

Implementation of a Picture Archiving and Communication System (PACS) is a system integration task and requires the knowledge of multidisciplinary fields. This paper reviews current PACS development with emphasis on radiological images. The following topics are covered: methods of image acquisition, image compression, storage, display, communication, and image database structure. Methods of implementation of PACS in a clinical environment as well as current operational PACS in hospitals are reviewed. A survey of private industry participating in PACS research and development are also given.

Hospital Information Systems↗
PubMedDate not supplied

Single exposure dual-energy digital radiography.

This study presents preliminary results of single kVp dual-energy computed radiography using laser stimulable luminescent phosphor image plate detectors. The single kVp technique makes use of four of these plates in a single cassette, each plate acting as an X-ray filter to the next so that the energy separation required for the dual-energy basis decomposition is achieved. An analysis to determine the best operating technique for the chest is performed using computer stimulation, and was found to be 85 kVp and 14 mAs. This technique yields the same entrance exposure value as is used clinically, so that the information for the decomposition is obtained without additional dose to the patient. The iso-transmission line technique was used as the decomposition algorithm. A humanoid chest phantom was used to demonstrate the quality of the resulting calibration material equivalent images.

Algorithms↗
PubMedDate not supplied

Picture archiving and communication system (PACS) networking: three implementation strategies.

This paper outlines the diverse Picture Archiving and Communication Systems (PACS) networking implementation strategies at the University of California at Los Angeles, the University of Florida, and the University of Kansas. At the University of California at Los Angeles, a very high-speed network has been integrated into a hierarchical networking strategy, resulting in an entirely customized network for the local transmission of images. The University of Florida has chosen to implement networks for local transmission of images using commercially available equipment. The University of Kansas, specializing in teleradiology applications, uses commercial telecommunication circuits to implement long distance referral services to small hospitals.

Florida↗
PubMedDate not supplied

PACS database architecture and design.

PACS (Picture Archiving and Communication Systems) database design requires careful understanding of the data and processing needs of radiologists, referring physicians, radiology staff, administrators, and researchers. Due to access requirements, the physical implementation for the management of small text data sets differs from the implementation strategy for large image data sets (centralized vs. distributed storage strategies). In this paper we discuss the database structure, storage architecture, file placement strategies, and administration considerations of the UCLA PACS.

Database Management Systems↗
PubMedDate not supplied

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.

Computer Communication Networks↗
PubMedDate not supplied

Single-exposure dual-energy computed radiography.

This paper focuses on analysis and development of a single-exposure dual-energy digital radiographic method using computed radiography (Fuji FCR-101 storage phosphor system). A detector sandwich consisting of storage phosphor imaging plates and an interdetector filter is used. The goal of this process is to provide a simple dual-energy method using typical plane-projection radiographic equipment and techniques. This approach exploits the transparency of the storage phosphor plates, using radiographic information that would be otherwise lost, to provide energy selective information essentially as a by-product of the radiographic examination. In order to effectively make use of the large dynamic range of the storage phosphor imaging plates (10,000:1), a computed radiography image reading mode of fixed analog-to-digital converter gain and variable photomultiplier sensitivity provides image data which can be related to relative incident exposure for export to the decomposition algorithm. Scatter rejection requirements necessitated crossed 12:1 grids for a field size of 36 x 36 cm. Optimal technique parameters obtained from computer simulation through minimization of the aluminum and Plexiglas equivalent image uncertainty under conditions of constant absorbed does resulted as: 100 kVp using a 0.15-mm-thick tin (Sn) interdetector filter for the lung field. This yields a surface exposure of 23 mR and a surface absorbed dose of 0.26 mGy for a 23-cm-thick chest. Clinical application in evaluation of the solitary pulmonary nodule is discussed, along with an image set demonstrating this application.

Computer Simulation↗