OBJECTIVE: To determine how Larsen scores from digitized X-rays compare to those from film originals. METHODS: A hundred sets of radiographs of patients recruited with early rheumatoid arthritis (RA) were assessed using the Larsen scoring system. Digitized copies of these sets were then viewed on a computer screen and scored according to Larsen in a random order. The quality of the digitized image was also recorded. For each set of X-rays, the signed difference between the score from film and the score from the digitized images was calculated. RESULTS: A total of 95% of the digitized X-ray sets were scored successfully; 5% were not scored due to the images being unreadable. The mean difference between the two sets of scores was -1.2 (95% CI [-2.06, -0.37]). There was no trend in the difference with respect to the mean of the two scores (P>0.1). CONCLUSION: The Larsen scoring of digitized X-ray images has been validated. (+info)
A new method of measuring propagation coefficients and characteristic impedance in blood vessels.
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True propagation coefficients of pulse wave harmonics in an artery can be determined in vivo by measuring pulsatile blood pressure and flow at each of two points along the length of the vessel. These coefficients, which are complex numbers that describe the attenuation and the phase shift imposed on a traveling wave, are independent of the reflected waves in the circulation and thus provide information about the viscoelastic state and other properties of an artery. The equations involved are implicit in standard transmission-line theory, but they have not previously been applied in this particular way to blood vessels. The femoral artery, exposed in situ, was studied in 11 anesthetized dogs. At 1.5 Hz, true attenuation constants averaged 0.0151 nepers/cm, and true phase constants averaged 0.0155 radians/cm. As frequency increased, the apparent phase velocity of flow, in contrast, was relatively low at the first harmonic and rose as frequency increased. True phase velocities lay between the apparent pressure and flow values. Characteristic impedance at 1.5 Hz had an average modulus of 1.76 times 10-4 dyne sec/cm5 and a phase of minus 0.31 radians. The modulus diminished as frequency increased, and the phase became less negative. These results show that true phase constants and characteristic impedances determined by this method are consistent with data reported by others and provide information not previously available about flow wave propagation. (+info)
Nonlinear contribution of eye velocity to motion perception.
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The aim of this study was to test the hypothesis that an extra-retinal signal combines with retinal velocity in a linear manner as described by existing models to determine perceived velocity. To do so, we utilized a method that allowed the determination of the relative contributions of the retinal-velocity and the extra-retinal signals for the perception of stimulus velocity. We determined the velocity (speed and direction) of a stimulus viewed with stationary eyes that was perceptually the same as the velocity of the stimulus viewed with moving eyes. Eye movements were governed by the tracking (or pursuit) of a separate pursuit target. The velocity-matching data were unable to be fit with a model that linearly combined a retinal-velocity signal and an extra-retinal signal. A model that was successful in explaining the data was one that takes the difference between two simple saturating non-linear functions, g and f, each symmetric about the origin, but one having an interaction term. That is, the function g has two arguments: retinal velocity, R, and eye velocity, E. The only argument to f is retinal velocity, R. Each argument has a scaling parameter. A comparison of the goodness of fits between models demonstrated that the success of the model is the interaction term, i.e. the modification of the compensating eye velocity signal by the retinal velocity prior to combination. (+info)
Characterization and use of a digital light projector for vision research.
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For creating stimuli in the laboratory, digital light projection (DLP) technology has the potential to overcome the low output luminance, lack of pixel independence, and limited chromaticity gamut of the cathode ray tube (CRT). We built a DLP-based stimulator for projecting patterns on the in vitro primate retina. The DLP produces high light levels and has good contrast. Spatial performance was similar to that of a CRT. Temporal performance was limited by the refresh rate (63 Hz). The chromatic gamut was modestly larger than that of a CRT although the primary spectra varied to a small degree with light output and numerical aperture. (+info)
An investigation of the centres of pressure under the foot while walking.
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The forces under the foot while walking have been measured using a high sensitivity force-plate of the strip-suspended type combined with simultaneous filming of the sole of the foot. The recording of data and the calculation and plotting of results were much simplified by computer aid. Normal and abnormal feet, both barefoot and shod, were investigated in sixteen subjects. It was found that in normal barefoot walking the forefoot carried a total load of the order of three times that of the heel. When footwear was worn the function of the forefoot was progressively reduced as the rigidity of the sole of the shoe increased. Painful conditions of the forefoot also produced a large reduction in the proportion of the total load transferred. (+info)
A small-conductance Ca(2+)-activated K+ current and Cl- current in rat dental pulp cells.
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We characterized a voltage-dependent ionic current in dental pulp cells on dental pulp slices using a nystatin perforated-patch recording configuration. The outward currents in dental pulp cells were inhibited by the following channel blockers: 1) Ca(2+)-free extracellular solution containing 10 mM Ba2+, 2) extracellular 400 nM apamin and 3) extracellular 300 nM 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS). On the other hand, 15 mM tetraethylammonium (TEA) did not inhibit the outward currents. The inhibitory effects of Ca(2+)-free extracellular solution, apamin and DIDS had voltage-dependency. These results indicated that dental pulp cells expressed a small-conductance Ca(2+)-activated K+ current (SK current) and a DIDS-sensitive Cl- current. The functional significance of these channels is discussed. (+info)
Computer-assisted mammographic imaging.
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Computer-assisted mammography imaging comprises computer-based analysis of digitized images resulting in prompts aiding mammographic interpretation and computerized stereotactic localization devices which improve location accuracy. The commercial prompting systems available are designed to draw attention to mammographic abnormalities detected by algorithms based on symptomatic practise in North America. High sensitivity rates are important commercially but result in increased false prompt rates, which are known to distract radiologists. A national shortage of breast radiologists in the UK necessitates evaluation of such systems in a population breast screening programme to determine effectiveness in increasing cancer detection and feasibility of implementation. (+info)
Ocular oscillations on eccentric gaze.
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Many normal individuals show ocular oscillations on eccentric gaze. This study was designed to investigate the effect of visual disengagement and visual feedback on the nature of these end point oscillations. Three test conditions were examined: target present, target absent and when the target position was determined by the subject's eye position via a variable feedback control system. Feedback gains (i.e. target velocity/eye velocity) ranged from 0, where the target position was decoupled from the subject's eye movements (i.e. the target is stationary on the screen), to +1.0 where the retinal image was stabilised (i.e. the target is driven by the subject's eye movements). Only subjects who exhibited sustained end-point oscillations with no latency were included in the study (n=6). Seven different oscillations including square-wave jerks were recorded in the abducting eye during eccentric gaze of a stationary target. The three most common oscillations were the jerk oscillations, with decelerating, linear or pendular slow phases. A number of additional previously unreported waveforms were also recorded. On removal of the target, the mean drift velocity of the slow phase was greatly reduced. The response to the introduction of a change in the visual feedback was specific to each subject, although in all cases, the end-point oscillations generally were of a lower velocity, and gaze was shifted by up to 8 deg in the direction of the slow phase within the first two seconds. The important role of slow eye movement control for maintaining gaze holding is discussed. (+info)