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At least 397 records · Page 22Linked to original sources
PubMed2003

Characteristics of spontaneous eyeblink activity during video display terminal use in healthy volunteers.

PURPOSE: To analyse the spontaneous eyeblink rate (SEBR) and inter-eyeblink intervals (IEBI) of normal volunteers before and during video display terminal (VDT) use. METHODS: The SEBR of 51 normal volunteers was measured by counting the absence of the corneal reflex using a computer-based video analysis system. Only complete eyeblinks were recorded within 10 min under three different conditions: during a conversation, during VDT use without corneal anaesthesia, and during VDT use with corneal anaesthesia. The IEBI (in seconds) were determined to study individual time-dependent changes of SEBR. RESULTS: In comparison with SEBR during conversation (mean 15.54 eyeblinks/min, standard deviation +/-13.74 eyeblinks/min) the SEBR decreased significantly during VDT use without corneal anaesthesia (5.34 +/- 4.53 eyeblinks/min). Corneal anaesthesia further significantly reduced SEBR (2.78 +/- 2.77 eyeblinks/min). The SEBR was characterized by marked interindividual variability, ranging between 11 and 664 eyeblinks/10 min during conversation, between 4 and 189 eyeblinks during VDT use without corneal anaesthesia and between 1 and 119 eyeblinks at VDT use with corneal anaesthesia. No significant correlation between SEBR (during conversation or during VDT use) and quality (break-up time) or quantity (Schirmer I test, Jones test) of the tear film could be detected. Evaluation of the IEBI revealed three different types of eyeblink pattern during VDT use without corneal anaesthesia. Type 1 was characterized by a very low SEBR (0-2 eyeblinks/min) and relatively homogeneous distribution of eyeblinks, type 2 showed a moderate SEBR (1.2-8.5 eyeblinks/min) including three further subtypes. Type 3 was characterized by a high SEBR (6.8-18.9 eyeblinks/min) of regular or irregular pattern. CONCLUSIONS: VDT use is associated with a profound decrease of the SEBR in healthy subjects. There are marked interindividual differences in SEBR and no correlation between the SEBR and ocular tear film parameters in normal eyes. The SEBR is further reduced by corneal anaesthesia. The presence of different patterns of eyeblinking may be related to various exogenous and endogenous factors and may lead to a better understanding of ocular reactions during VDT use.

Adult↗
PubMed1990

Computer study of presynaptic inhibition controlling the spread of action potentials into axonal terminals.

1. The effect of presynaptic, axoaxonal inhibition, that exerts its action by producing a local conductance increase, on the behavior of action potentials at postsynaptic axon terminals is analyzed computationally. The significance of the location and strength of the presynaptic inhibition, as well as the morphology and membrane properties of the axonal terminals, are considered. 2. Keeping the specific properties of terminal membrane and axoplasm constant, the critical "silent" steady-state conductance change (gcrit) that blocks propagation is linearly scaled with the terminal diameter raised to the 3/2 power. At the midpoint of a 5 lambda long, 1 micron diameter axon that has the standard Hodgkin and Huxley (1952) kinetics at 18 degrees C (and an input conductance of 8.7 nS), gcrit is 72 nS. At 0 degrees C, gcrit = 200 nS, whereas at 30 degrees C gcrit = 30 nS. 3. The critical conductance change that blocks propagation depends steeply on the density of excitable channels (gNa) at the terminal. For a geometrically uniform terminal at 18 degrees C, the action potential can not be blocked by a local shunt when gNa greater than 600 mS/cm2. 4. An axoaxonal synapse in the proximity of the postsynaptic release site has graded control over the spike amplitude (and, therefore, over the postsynaptic output) at that site. Presynaptic inhibition located remotely from the release site has an all-or-none effect at the release site. 5. Inhibition is more effective in attenuating the spike at the terminal when it impinges onto a passive terminal rather than on an excitable one. 6. The detectability of the conductance increase as well as the change in action potential amplitude associated with the presynaptic inhibition is poor at only a short distance from the axoaxonal synapse. The presence of bottlenecks and varicosities at some axonal terminals enhances this decoupling effect even more. Thus presynaptic inhibition may reduce the potential near the output site of the affected axon significantly, without producing any noticeable conductance or voltage change at a distance of only several tens of micrometers (a few tenths of a space constant) away from it. 7. Varicosities and bottlenecks typically found along axonal terminals are the optimal loci for presynaptic inhibition to be most effective in attenuating the action potential at the terminal. Even with high density of excitable channels, propagation with such terminal geometry is insecure, and one, or few, quanta of inhibitory transmitter (a conductance change of several nanosiemens) can block propagation there.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1997

A pilot study of eye movement during mammography interpretation: eyetracker results and workstation design implications.

Digital mammography can potentially improve mammography image and interpretation quality. On-line interpretation from a workstation may improve interpretation logistics and increase availability of comparison images. Interpretation of eight 4k- x 5k-pixel mammograms on two to four 2k- x 2.5k-pixel monitors is problematic because of the time spent in choosing which images display on which monitors, and zooming and roaming on individual images that are too large to display completely at full resolution. The authors used an eyetracker to measure radiologists viewing behavior during mammography interpretation with film on a viewbox. It was observed that a significant portion of the mammographers' time is spent viewing "comparison pairs" (typically two or more comparisons per case), such as the left mediolateral and craniocaudal images or old and new images. From the eyetracker measurements, we estimated that the number of image display, roam, and zoom operations decreases from an average of 64 for one monitor to 31 for four monitors, with the largest change going from one to two monitors. We also show that fewer monitors with a faster response time is superior to more monitors with a slower response time. Finally, the authors demonstrate the applicability of time-motion analysis to mammographic workstation design.

Adult↗
PubMed1995

The health care professional multimedia workstation: development and integration issues.

Workstations for health care professionals provide access to distributed healthcare information systems. They are complex systems that have to manage, in a unified framework, the distributed and multimedia information needed for optimal patient care. The objective is to provide the end-user with a virtual and unified device that conceals the complexity of the underlying information system. Integration and reuse of modular software components are important in the development of such a workstation. A reference set of evaluation criteria is proposed that includes functional, technical, organizational, medical, cultural and ethical, economic and industrial components.

Computer Communication Networks↗
PubMed2002

Calibrated LCD/TFT stimulus presentation for visual psychophysics in fMRI.

Standard projection techniques using liquid crystal (LCD) or thin-film transistor (TFT) technology show drastic distortions in luminance and contrast characteristics across the screen and across grey levels. Common luminance measurement and calibration techniques are not applicable in the vicinity of MRI scanners. With the aid of a fibre optic, we measured screen luminances for the full space of screen position and image grey values and on that basis developed a compensation technique that involves both luminance homogenisation and position-dependent gamma correction. By the technique described, images displayed to a subject in functional MRI can be specified with high precision by a matrix of desired luminance values rather than by local grey value.

Brain Mapping↗
PubMed1999

Detection of caries with conventional digital imaging and tuned aperture computed tomography using CRT monitor and laptop displays.

OBJECTIVE: The purpose of this study was to compare the diagnostic performance of conventional digital images and tuned aperture computed tomography (TACT) slices in caries detection through use of cathode-ray tube monitor and laptop displays. STUDY DESIGN: Forty-two extracted posterior teeth were mounted and imaged with a direct digital radiography system. Conventional digital bitewing projections and TACT slices were acquired. Images were viewed on a high-resolution cathode-ray tube monitor and on an active-matrix laptop display. Eight observers assessed caries status of occlusal and proximal surfaces of the teeth using all combinations of image and display modality. Observers' assessments were compared with the results of histologic examination of tooth sections. Possible differences in receiver operating characteristic curve areas among displays, image modalities, observers, and surfaces were analyzed by means of analysis of variance. RESULTS: There was no statistically significant difference between the diagnostic performances provided by the cathode-ray tube monitor and laptop displays in caries detection (P = .588). In addition, the performances of digital images and TACT slices were not significantly different (P = .843). CONCLUSIONS: Modern active-matrix laptop displays provide diagnostic quality for caries detection comparable to that obtainable with cathode-ray tube monitors.

Analysis of Variance↗
PubMed2002

Evaluation of accuracy of computer-aided intraoperative positioning of endosseous oral implants in the edentulous mandible.

The overall accuracy of a novel surgical computer-aided navigation system for placement of endosseous implants was evaluated. Five dry cadaver mandibles were scanned using high resolution computed tomography (HRCT). The position of four interforaminal dental implants was planned on the computer screen and transferred to the cadaver mandibles using VISIT, a surgical navigation software developed at the Vienna General Hospital. The specimens were HRCT-scanned again to compare the position of the implants with the preoperative plan on reformatted slices after matching of the pre- and postoperative data sets using the mutual information technique. The overall accuracy was 0.96 +/- 0.72 mm (range 0.0-3.5 mm). No perforation of the mandibular cortex or damage to the mandibular canal occurred. We conclude that computer-aided implant surgery can reach a level of accuracy where further clinical developments are feasible.

Cadaver↗
PubMed1992

Visual increment and decrement threshold curves as a function of luminance range and noise in simulated computed tomographic scans.

OBJECTIVES: The effect of luminance range compression on the visual threshold of a target in a computed tomographic (CT) scan was investigated in eight experiments. METHODS: Both visual increment thresholds of a hot target and visual decrement thresholds of a cold target were obtained. Realistic noisy CT images simulating a scan reconstruction and partial volume blurring were tested as representative of complex medical images. Negative versions, high luminance versions, and noise-free versions of these CT images also were tested. RESULTS AND CONCLUSIONS: In all the noisy images, as the luminance range of the image was compressed, proportionately smaller physical luminance differences between the target and its local background were needed to reach visual threshold. However, the thresholds were the same in terms of the difference in CT numbers between target and background. Noise in terms of CT numbers sets the threshold for a wide range of display conditions. In the noise-free CTs, as the luminance range was compressed, the luminance differences between the target and background needed to reach threshold also decreased, but only marginally. However, in terms of CT numbers, the thresholds were increased.

Analysis of Variance↗
PubMed1992

A universal system for interactive image-directed neurosurgery.

Stereotactic methods confer great accuracy to intracranial target localization, but require strict adherence to a complex program of mechanical and computational maneuvers. A computerized, articulated, localizing 'arm' has been developed that frees the neurosurgeon of these constraints and provides a completely intuitive, 'user-friendly' interface. This universal system is independent of whatever localizing fiducial system is selected. The arm may be sterilized for intracranial use. A variety of intraoperative end effectors may be selected. The patient's CT/MR/PET scans are loaded into computer memory and a three-dimensional shaded surface wireframe diagram of the patient's head is displayed simultaneously with up to 3 independent sets of cross-referenced CT/MR/PET scan images on the intraoperative video screen. The arm's endpoint location and the directional vector are shown as cursors on the relevant scan slices, and change continuously as the surgeon moves the arm. Because the information is continuously updated, an unlimited number of targets and trajectories may be displayed throughout the operation. The arm has an ultimate design accuracy for end-point localization to within 0.1 mm throughout a target volume of 40 x 40 x 40 cm. The tested application accuracy of the first prototype model is 0.31 mm. In clinical use during 30 surgeries, its real-world application accuracy is 0.9 mm. This system provides stereotactic accuracy and universally compatible, intuitive, interactive operation.

Biopsy↗
PubMed2005

Short communication: A method for verified access when using soft copy display.

Soft copy display is a rapidly developing area. To date, most soft copy systems can be classed by their application, e.g. review or reporting. With technology convergence this distinction is becoming less defined by the hardware and more defined by the software functionality. Although it is accepted that routine quality assurance should be conducted on soft copy monitors, this would be logistically difficult to achieve if any monitor within a hospital could be used for image review or reporting. This work proposes a simple psychophysical check to ensure optimal display performance before viewing software can be run. This is in the form of a challenge/response code constructed from letters just above the threshold of detection. This verified login would act as a portal to launching the image viewing software. The developed system was tested on three different types of monitor and five observers. Results indicate that the verified login was able to control access for displays below the optimal settings but was not as sensitive for adjustments above the optimum. However it is believed this is still of value as the lower presentation will compress the display gamma curve and reduce detail contrast. It also provides a minimum level of audit and quality control that might otherwise be missing.

Computer Communication Networks↗
PubMed1995

Image quality control for digital mammographic systems: initial experience and outlook.

This report presents (1) a broad topical review and a tutorial of the possibilities for image quality control (IQC) with digital systems, and (2) results and initial experience for IQC with two commercial digital imaging systems, but with limited discussion on any particular method. Digital imaging systems used for mammographically guided digital stereotactic breast biopsy were evaluated extensively at the University of Arizona. Measurements were made of linearity, sensitivity, signal-to-noise ratio, and square-wave modulation. Images of phantoms such as the American College of Radiology Accreditation Phantom and the contrast detail mammography Phantom were evaluated as well as images of the x-ray source's focal spot. The evaluation also included the cathode ray tubes for the imaging systems. The data collected show that digital imaging systems have an important advantage over film-screen systems because they provide a digital signal as output that can be used for quantitative analysis. As a result, IQC can become a much more quantitative discipline than presently practiced, providing more information on the imaging systems under evaluation, and providing better control over their properties during actual operation.

Computer Terminals↗
PubMed2004

Marked reduction and distinct patterns of eye blinking in patients with moderately dry eyes during video display terminal use.

PURPOSE: To analyze the spontaneous eye-blink rate (SEBR) and blinking pattern in patients with moderately dry eyes during video display terminal (VDT) use. METHODS: The SEBR of 30 patients with dry eye syndrome (median age 44.8 years, range 18 - 67 years) was measured using a computer-based video analysis system. Only complete eye blinks were recorded during 10 min of conversation, during initial VDT use and again after a preceding work period of 30 min. RESULTS: In comparison with SEBR during conversation (mean value 16.8 blinks/min, standard deviation 16.8 blinks/min) the SEBR significantly decreased during initial VDT use (6.6+/-4.8; P<0.001) and remained significantly decreased during re-measurement after 30 min (5.9+/-4.6; P<0.001). SEBR was not significantly different between initial VDT use and re-measurement after 30 min ( P=0.65). The SEBR was characterized by marked interindividual variability during conversation and VDT use. No significant correlation was found between SEBR (either during conversation or during VDT use), and the quality (tear break-up time) or quantity (Schirmer I test, Jones test) of the tear film. Typical blinking patterns were found to be (1). a relatively time-independent, irregular pattern, (2). an initial phase of 2-4 min with shorter inter-eye-blink intervals, and (3). alternating periods of higher and lower inter-eye-blink intervals. CONCLUSIONS: Reduction of the SEBR during VDT use is primarily determined by marked visual attention, resulting in an exacerbation of dry eye symptoms in predisposed humans. High interindividual variability and distinct patterns of eye blinking may be key factors in further clarification of VDT-eye interactions and develop individually designed solutions to prevent desiccation during VDT use.

Adolescent↗
PubMed2001

Evaluation of a head-mounted display (HMD) in the performance of a simulated laparoscopic task.

BACKGROUND: Head-mounted display (HM) units are used in various industries, but they have been tried only recently in surgery. In this study, we evaluated whether a commercially available HMD would improve or impede a laparoscopic task-in this case, suturing. METHODS: Six participants performed a total of 120 laparoscopic suture knots in an experimental model. The Olympus FMD011 model with a two-dimensional image was used. The order of each task with or without the head display unit was random. The time to complete each knot was recorded, and the results were analyzed. RESULTS: The display unit prolonged the suturing times of the subjects by 10% (p < 0.04). CONCLUSIONS: In this experimental model, the HMD we utilized did not appear to improve laparoscopic suturing. More developments, such as improved depth perception and better resolution, may increase its usefulness for laparoscopic tasks.

Computer Simulation↗
PubMed2004

Design requirements for radiology workstations.

This article stresses the importance of capturing feedback from representative users in the early stages of product development. We present our solution to producing quality requirement specifications for radiology workstations, specifications that remain valid over time because we successfully anticipated the industry trends and the user's needs. We present the results from a user study performed in December 1999 in a radiology clinic equipped with state-of-the-art Picture Archiving and Communications Systems (PACS) and imaging scanners. The study involved eight radiologists who answered questions and provided comments on three complementary research topics. First, we asked our subjects to enumerate the advantages and the disadvantages for both softcopy and hardcopy reading. We identified the two major factors for productivity improvement through the use of PACS workstations: workflow re-engineering and process automation. Second, we collected radiologist feedback on the use of hanging protocols (HPs). The results indicated the high importance of automatic image organization through HPs, with the potential effect of reducing the interpretation time by 10-20%. Our subjects estimated that 10-15 HPs would cover about 85%-95% of the regular radiological examinations. Third, we investigated the impact of the display devices on the radiologist's workflow. Our results indicated that the number and the properties of the monitors is a modality-specific requirement. The main results from this study on key functional requirements for softcopy interpretation only recently were incorporated in most of the current, successful PACS workstations.

Attitude of Health Personnel↗
PubMed1994

The effects of computer interface design on human postural dynamics.

The main objective of this study was to examine the effects of human-computer interface design on postural dynamics, i.e., changes in working postures and postural discomfort exhibited by operators of the computer-based remote bar coding (RBC) system. In addition, the effects of different work/rest schedules on postural dynamics were evaluated. Twelve subjects participated in the laboratory experiment, which consisted of twelve scenarios utilizing two cognitive task requirement factors, i.e., (1) information presentation mode, defined through the letter image preview on the computer screen (none or one preview image); and (2) the information processing mode, defined through the specific keying method (key all characters or key 5 digits only). The third experimental factor was the work/rest schedule (50 min work/10 min break, 2 h of work/15 min break, or flexible schedule). The results showed that requirements of human-computer interface design significantly affected the operators' postural dynamics. It was concluded that not only the physical, organizational, or psychosocial work environment characteristics, but also the cognitive task characteristics are important for assessment of postural effects in the VDT work. The relationship between interface design, mental workload and postural dynamics should be carefully considered in future studies aimed at optimizing the human-computer data entry tasks.

Adult↗
PubMed2005

Ergonomics, musculoskeletal disorders and computer work.

This review summarizes the knowledge regarding ergonomics and musculoskeletal disorders and the association with computer work. A model of musculoskeletal disorders and computer work is proposed and the evidence and implications of the model together with issues for future research is discussed. The model emphasizes the associations between work organization, psychosocial factors and mental stress on the one hand and physical demands and physical load on the other. It is hypothesized that perceived muscular tension is an early sign of musculoskeletal disorder, which arises as a result of work organizational and psychosocial factors as well as from physical load and individual factors. It is further hypothesized that perceptions of exertion and comfort are other possible early signs of musculoskeletal disorders in computer work. Interventions aimed at reducing musculoskeletal disorders due to computer work should be directed at both physical/ergonomic factors and work organizational and psychosocial factors. Interventions should be carried out with management support and active involvement of the individual workers.

Computer Terminals↗