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At least 379 records · Page 21Linked to original sources
PubMed1994

Computer-assisted 3D reconstruction of the terminal branches of the cerebral arteries. III. Posterior cerebral artery and circle of Willis.

We present a three-dimensional anatomical computer model of the terminal branches of the posterior cerebral artery and circle of Willis, acquired from equidistant serial anatomical slices of three brains. The reconstructions provide a clear picture from all angles of the complicated course of the terminal branches of the cerebral arteries. This can help to identify the arteries in conventional and magnetic resonance angiography. Our rendition of the cerebral arteries can be matched with CT, MR und PET images to indicate the areas of extension of the individual branches, allowing neuromorphological and functional correlations.

Basilar Artery↗
PubMed1996

Accommodative and binocular vision disorders associated with video display terminals: diagnosis and management issues.

BACKGROUND: With the rapid computerization of the workplace, school and home office, it is likely that a vast majority of Americans will be using computers for significant amounts of time in the near future. Research has demonstrated a high prevalence of accommodative and binocular vision disorders in symptomatic VDT users, which underscores the importance of the assessment and management of accommodation and binocular vision for patients working with computers. METHODS/RESULTS: This paper presents a simplified approach for the diagnosis and management of accommodative and binocular vision disorders in VDT users. The emphasis is on modifications of the traditional examination routine to make the assessment as sensitive as possible to the vision problems associated with VDT use. CONCLUSIONS: To meet the needs of symptomatic VDT users, optometrists must perform a comprehensive assessment of accommodation and binocular vision. The use of appropriate testing, when combined with attention to the environmental factors associated with VDT use, will enable optometrists to understand the reasons for symptoms and design an effective treatment program.

Accommodation, Ocular↗
PubMed2002

The use of video refraction to measure the dynamic properties of the near triad in observers of a 3-D display.

OBJECTIVE: Recording of the dynamic behaviour of the near triad during viewing of a three-dimensional (3-D) display is attempted. This may then be used to identify the possible origin of asthenopia and other ocular problems which occur whilst viewing such displays. METHODS: Subjects viewed a 3-D display through an image splitter. Video recordings of ocular responses (pupil diameter, vergence and accommodation) were made with a commercially available video refraction unit at a distance of 1.2 m from the subject. Continuous recordings were made whilst a step-wise disparity of up to 2.6 degrees was introduced between the targets presented to the two eyes, but the accommodative stimulus remained unchanged. Image analysis from the recordings was carried out on a personal computer. RESULTS: Results showed various complex patterns of response, with the accommodation and vergence recorded reflecting the effect of stimulus conflict. Difficulty in fusional convergence was recorded when disparity was large, and the recordings reflected the subjects' comments. CONCLUSION: The video refraction method is a useful tool for studying the dynamic behaviour of the near triad.

Accommodation, Ocular↗
PubMed2001

Generation of TACT image slices using different reconstruction algorithms: effects on natural caries detection.

OBJECTIVE: The purpose of this study was to determine whether the method of reconstruction of tuned-aperture computed tomography (TACT) slices has an influence on observer performance in caries detection. STUDY DESIGN: Eight images of each of 40 extracted posterior teeth were acquired by using a solid state intraoral detector. Stacks of tuned-aperture computed tomography slices were generated by using the minimum and average reconstruction methods. Slices of the 2 experimental conditions were presented to 8 observers in a balanced order. Images were viewed on a high-resolution 21-in color monitor. Observers scored the presence/absence of caries by using a 5-point confidence scale. Observers' assessments were compared with histologic examinations of tooth sections. Receiver operating characteristic curves measured observers' diagnostic performance. Analysis of variance was used to test for possible significant differences between observers and between experimental conditions. Sensitivity, specificity, accuracy, and interobserver reliability were also calculated. RESULTS: No statistically significant differences between the 2 methods of reconstruction were found for the detection of either occlusal (P =.07) or proximal (P =.52) caries. Interobserver reliability was similar for both experimental conditions. CONCLUSIONS: The minimum and average methods of TACT reconstruction provide comparable performances for caries detection tasks.

Algorithms↗
PubMed2003

An application framework for computer-aided patient positioning in radiation therapy.

The importance of exact patient positioning in radiation therapy increases with the ongoing improvements in irradiation planning and treatment. Therefore, new ways to overcome precision limitations of current positioning methods in fractionated treatment have to be found. The Department of Medical Physics at the German Cancer Research Centre (DKFZ) follows different video-based approaches to increase repositioning precision. In this context, the modular software framework FIVE (Fast Integrated Video-based Environment) has been designed and implemented. It is both hardware- and platform-independent and supports merging position data by integrating various computer-aided patient positioning methods. A highly precise optical tracking system and several subtraction imaging techniques have been realized as modules to supply basic video-based repositioning techniques. This paper describes the common framework architecture, the main software modules and their interfaces. An object-oriented software engineering process has been applied using the UML, C + + and the Qt library. The significance of the current framework prototype for the application in patient positioning as well as the extension to further application areas will be discussed. Particularly in experimental research, where special system adjustments are often necessary, the open design of the software allows problem-oriented extensions and adaptations.

Computer Terminals↗
PubMed2004

Genome-wide prediction of stop codon readthrough during translation in the yeast Saccharomyces cerevisiae.

In-frame stop codons normally signal termination during mRNA translation, but they can be read as 'sense' (readthrough) depending on their context, comprising the 6 nt preceding and following the stop codon. To identify novel contexts directing readthrough, under-represented 5' and 3' stop codon contexts from Saccharomyces cerevisiae were identified by genome-wide survey in silico. In contrast with the nucleotide bias 3' of the stop codon, codon bias in the two codon positions 5' of the termination codon showed no correlation with known effects on stop codon readthrough. However, individually, poor 5' and 3' context elements were equally as effective in promoting stop codon readthrough in vivo, readthrough which in both cases responded identically to changes in release factor concentration. A novel method analysing specific nucleotide combinations in the 3' context region revealed positions +1,2,3,5 and +1,2,3,6 after the stop codon were most predictive of termination efficiency. Downstream of yeast open reading frames (ORFs), further in-frame stop codons were significantly over-represented at the +1, +2 and +3 codon positions after the ORF, acting to limit readthrough. Thus selection against stop codon readthrough is a dominant force acting on 3', but not on 5', nucleotides, with detectable selection on nucleotides as far downstream as +6 nucleotides. The approaches described can be employed to define potential readthrough contexts for any genome.

Codon, Terminator↗
PubMed2002

A modified Perkins Brailler for text entry into windows applications.

In this paper, we describe how a Perkins Brailler can be adapted so that it can function as a keyboard to a personal computer. The paper describes the earlier work of others and the hardware and software of our system and concludes with indications of how the system may be improved.

Blindness↗
PubMed2004

Noise in flat-panel displays with subpixel structure.

Subpixel structures found in medical monochrome active-matrix liquid crystal displays (AMLCDs) affect noise estimates measured with conventional methods. In this work, we discuss methods that identify sources of noise and permit the comparison of luminance noise estimates across technologies independent of pixel design and device technology. We used a three-million pixel AMLCD with a pixel structure consisting of three color stripes, each in a two-domain, in-plane switching mode. Images of uniform fields displayed on the AMLCD were acquired using a low-noise, high-resolution CCD camera. The camera noise and flat-field response were characterized using a uniform light source constructed for this purpose. We show results in terms of spatial luminance noise and noise power spectrum for high-resolution images and for the same images processed with a pixel-aligned aperture. We find that the pixel-aligned aperture eliminates almost all the noise found in the high-resolution images, suggesting that most of the luminance noise in AMLCDs comes from the subpixel structure and less-than-100% aperture ratio, rather than from interpixel variations.

Computer Terminals↗
PubMed1999

Accuracy and availability of the computed assisted neurosurgery navigation system during epilepsy surgery.

The magnetic-force-based Computed Assisted Neurosurgery System was used for epilepsy surgery to localize targets accurately in the operative field. The correlation between X components of target coordinates in the axial plane and the coronal plane for the same target was strong in all cases. Concerning Y components, there were statistically significant differences in 2 cases. There was a case that showed statistically significant differences only in the Z dimension. The interdisk distance by data sets of coordinates obtained from neuronavigation was calculated to quantify localization error, and the measuring error ranged from -5 to 13.3 mm (1.3 +/- 3.2 mm). The magnitude of the application errors in this study tended to be large in the frontal and vertex regions.

Adolescent↗
PubMed1997

A note on luminance calibration of raster-scan cathode-ray tubes: temporal resolution, ripple, and accuracy.

Accurate luminance calibration is an important issue for stimuli in vision research. Raster-scan cathode-ray tubes present a rapidly scanning spot with a luminance of the order of 10,000 cd m-2 (the actual value depends on video timing and phosphor persistence). With little spatial integration this may result in overloading of the front stage of a photometer. More importantly, even if averaged over hundreds of milliseconds, the pulsed nature of the luminance signal will markedly reduce accuracy of the luminance measurement. A frame-synchronised photometer is described to increase measurement accuracy whilst still rapidly acquiring the result.

Computer Terminals↗
PubMed2003

A practical approach to soft-copy display consistency for PC-based review workstations.

The use of non-permanent, digital image display, i.e. soft-copy display, is increasing within hospitals due to the growth in the use of digital modalities and picture archiving and communication systems (PACS). Non-dedicated image review using standard PCs is being employed as a cost-effective method of image access. These workstations do not have specialized display systems and are likely to suffer from inconsistent image presentation. The Digital Imaging and Communications in Medicine (DICOM) Working Group 11 has developed a display function standard (part 14) to standardize the display of grey scale images. Although this standard is starting to be adopted by manufacturers of proprietary reporting systems it is not easily applied to the existing number of non-dedicated, PC-based review systems. The aim of this work was to investigate whether display consistency could be achieved simply and reproducibly on these systems, outside of the DICOM standard: part 14, by adjusting monitor brightness and contrast settings and using the Society of Motion Picture and Television Engineers (SMPTE) digital test pattern. The study showed that by adjusting the brightness and contrast settings alone it was possible to approximate the display characteristic curves to the grey scale standard display function (GSDF) defined in the DICOM standard: part 14, but only at unacceptably low luminances. Intradisplay and interdisplay consistency could be achieved using a simple monitor set-up procedure and the SMPTE test pattern.

Computer Terminals↗
PubMed2001

Eye activity correlates of workload during a visuospatial memory task.

Changes in six measures of eye activity were assessed as a function of task workload in a target identification memory task. Eleven participants completed four 2-hr blocks of a mock anti-air-warfare task, in which they were required to examine and remember target classifications (friend/enemy) for subsequent prosecution (fire upon/allow to pass), while targets moved steadily toward two centrally located ship icons. Target density served as the task workload variable; between one and nine targets were simultaneously present on the display. For each participant, moving estimates of blink frequency and duration, fixation frequency and dwell time, saccadic extent, and mean pupil diameter, integrated over periods of 10 to 20 s, demonstrated systematic changes as a function of target density. Nonlinear regression analyses found blink frequency, fixation frequency, and pupil diameter to be the most predictive variables relating eye activity to target density. Participant-specific artificial neural network models, developed through training on two or three sessions and subsequently tested on a different session from the same participant, correlated well with actual target density levels (mean R = 0.66). Results indicate that moving mean estimation and artificial neural network techniques enable information from multiple eye measures to be combined to produce reliable near-real-time indicators of workload in some visuospatial tasks. Potential applications include the monitoring of visual activity of system opetators for indications of visual workload and scanning efficiency.

Adult↗
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↗