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Biomedical subjects

B K Stewart

Publications and source records attributed to B K Stewart.

At least 19 recordsLinked to original sources
PubMed1997

Application of a 3D volume 19F MR imaging protocol for mapping oxygen tension (pO2) in perfluorocarbons at low field.

A limited flip angle gradient-echo 3D volume acquisition imaging protocol for mapping partial pressure of oxygen (pO2) in perfluorocarbon compounds (PFCs) at low field (0.14 T) is presented. The PO2 measurement method is based on the paramagnetic effect of dissolved molecular oxygen (O2) which reduces the PFC 19F T1. Specific objectives related to imaging of PFCs through use of the protocol include improved image signal-to-noise characteristics and elimination of 19F chemical shift artifacts. A parametric Wiener deconvolution filtering algorithm is used for suppression of 19F chemical shift artifacts. Application of the protocol is illustrated in a series of calculated PO2 maps of a gas equilibrated, multi-chamber phantom containing perfluorotributylamine (FC-43). The utility of the protocol is demonstrated in vivo through images of a commercially available perfluorocarbon based blood substitute emulsion containing FC-43 sequestered in the liver and spleen of a rat.

Algorithms↗
PubMed1995

Biochemical discrimination of pathologic pregnancy from early, normal intrauterine gestation in symptomatic patients.

The authors have examined the utility of using the rate of change of the human chorionic gonadotropin (hCG) level and progesterone concentration to distinguish ectopic from normal intrauterine pregnancies. Patients suspicious for ectopic pregnancy had three outcomes: normal intrauterine gestation (NIUG), ectopic pregnancy (ECT), and inevitable abortion (IAB). The rate of change of the hCG level and the progesterone concentration distinguish NIUG from ECT with good sensitivity and specificity at optimal cut-offs of 0.14 (rate of change of the logarithm of hCG) and 8 ng/mL (progesterone). As the biochemical parameters of the ECT and IAB groups overlap, stating that NIUG can be biochemically distinguished from ECT is misleading. Thus, the authors have grouped them together as pathologic pregnancies (PATH). The rate of change of the hCG level and the progesterone concentration distinguish NIUG from PATH with good sensitivity and specificity with the same optimal cut-offs of 0.14 (rate of change of the logarithm of hCG) and 8 ng/mL (progesterone).

Abortion, Spontaneous↗
PubMed1995

Use of the fluorochrome calcofluor white in the screening of stool specimens for spores of microsporidia.

Microsporidia are obligate intracellular protozoal pathogens associated with chronic diarrhea in individuals infected with HIV. Direct detection methods for microsporidial spores in stool include chromotrope-based, fluorochrome, and immunofluorescent stains. The authors compared the ability to detect microsporidial spores in 168 stool specimens using two stains: a chromotrope-based modified trichrome stain and a fluorochrome stain, calcofluor white (Cellufluor, Polysciences, Warrington, PA). In addition to being faster and easier to perform, the calcofluor white stain was found to be more sensitive than the chromotrope-based stain, as 6 of 24 specimens positive by calcofluor white were negative by the chromotrope-based stain on initial smear evaluation. Repeat examination confirmed these six as being positive. To evaluate the specificity of the calcofluor white stain, 20 formalin-fixed stool specimens (5 positive and 15 negative for microsporidial spores) were evaluated in blinded fashion by two affiliated clinical laboratories using their own formulations of calcofluor white. A single discrepant result (falsely positive) was reported from one laboratory. The use of the calcofluor white stain is recommended as a simple and highly sensitive screening procedure for the detection of microsporidial spores in stool specimens.

Animals↗
PubMed1995

Use of data in a radiology information system for labeling computed radiographs: an interface to connect the two systems.

Computers have greatly facilitated the processing and storage of radiologic information. Manufacturers of radiology information systems (RISs) are gradually incorporating options for interfacing their products with other computers (e.g., hospital information systems). However, a growing need exists to also interface RISs with digital radiologic equipment so that images (e.g., computed radiographs of the chest and skeleton) are automatically labeled with identification data. Such connectivity would eliminate redundant work by technologists, decrease errors in the labeling of images, and increase the consistency of patients' data within a radiology department. Unfortunately, the rapid advances in digital technology, combined with the lack of a well-defined standard for the transfer of demographic information between dissimilar systems, have delayed development of these interfaces. We have developed a widely applicable method to automatically transfer patients' demographic data from an RIS to a commercially available computed radiography system. A personal computer is configured with inexpensive programmable telecommunications software to create an interactive gateway, which eliminates the need for redundant data entry (compared with entering data once on the RIS and again on the stand-alone computed radiography system), and thus also decreases errors in the labeling of images.

Local Area Networks↗
PubMed1994

Functionality of gray-scale display workstation hardware and software in clinical radiology.

This article examines the functional factors crucial for the successful conversion from film-based radiography to radiologic gray-scale display systems, including hardware architecture and software requirements, radiologic workstation operations, and a multilayered intelligent user interface. Radiologic workstation operations are logically decomposed into case preparation, case selection, case presentation, case interpretation, and documentation and presentation of the diagnosis. A multilayered software architecture for an adaptive, intelligent user interface is proposed: a hardware interface layer, an object-oriented layer, and a knowledge-based layer. The knowledge-based layer is composed of three elements: image presentation based on context-dependent models of diagnostic requirements, knowledge-based expert systems for assistance in diagnostic decision making, and computer-assisted diagnosis to alert the radiologist to potential lesions or abnormalities.

Diagnosis, Computer-Assisted↗
PubMed1993

Operational departmentwide picture archiving communication system analysis using discrete event-driven block-oriented network simulation.

The accurate prediction of image throughput is a critical issue in planning for and acquisition of any successful picture archiving and communication system (PACS). Simulation plays an important role in this effort. The PACS image management chain is decomposed into eight subsystems. These subsystems include network transfers over three different networks and five software programs and/or queueing structures. This decomposition is used to create a simulation model that was effectuated using commercially available block-oriented network simulation software. From the PACS database, the traffic generation patterns of the imaging modality devices are used to drive the simulation. The simulation models the image file flow through the PACS for a 24-hour period. The behavior of the simulated traffic generators agreed well with the values derived from the PACS database. The mean delay for the simulated PACS is found to be 225 +/- 59 seconds. The delay time was found to vary during the simulated 24-hour cycle in a consistent manner with observations. This simulation provides estimates on what a radiological department can expect from a PACS in terms of throughput, utilization, and delay. The block-oriented network simulator (BONeS, Comdisco Systems Inc, Foster City, CA) simulation model of the modeled PACS is highly accurate. The models for the imaging modality traffic sources are validated with a high degree of accuracy. The simulation model allows for the study of what happens to the delay time under various loads. In this simulation, the reformatting process was determined to be the bottleneck causing a large increase in delay time under heavy loads.

Computer Communication Networks↗
PubMed1993

The effect of irreversible image compression on diagnostic accuracy in thoracic imaging.

RATIONALE AND OBJECTIVES: Digital image compression reduces the storage requirements and network traffic on picture archiving and communications systems. Full-frame bit-allocation (FFBA) is an irreversible image-compression method based on the discrete cosine transform that provides for high compression ratios with a high degree of image fidelity. METHODS: One hundred twenty-two posteroanterior chest radiographs were obtained on patients in an ambulatory patient setting, including 30 cases of interstitial lung disease, 45 images containing combinations of lung nodules (N = 37) or mediastinal masses (N = 39), and 47 normal images containing none of the pathology for which we were testing. The images were digitized (nominal 2 K x 2 K x 12-bit resolution), printed on a 35 x 35-cm hard copy format, and compressed at an approximate compression ratio of 20:1. Observer performance tests were conducted with five radiologists using receiver operating characteristics analysis on digitized uncompressed and compressed hard copy images. RESULTS: There were no significant differences between the two display conditions for the detectability of any of the thoracic abnormalities. CONCLUSIONS: Our preliminary results suggest that irreversible image compression at ratios of 20:1 may be acceptable for use in digital thoracic imaging.

Algorithms↗
PubMed1993

Modeling of analog film-file radiographic retrievals. A Markov chain.

RATIONALE AND OBJECTIVES: Existing retrieval models for radiology film libraries have not incorporated the influence of previous retrievals. A Markov chain model for the retrieval rates from an analog film library is proposed as a means of considering this effect. METHODS: A Markov chain model was developed for the retrieval rates of an analog film library. The Markov chain model required identification of the states of the Markov chain, the required one-step transition probabilities between states, and the initial state probabilities. RESULTS AND CONCLUSIONS: The results from the Markov chain model compared favorably with the 30-day measurements (25,775 retrievals), but a large enough sample to determine a statistical confidence level was not considered.

Academic Medical Centers↗
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↗