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At least 649 records · Page 36Linked to original sources
PubMed1984

Precision of digitized M-mode echocardiograms for clinical practice.

Computer digitization of M-Mode echocardiograms has proved a valuable research tool in the study of left ventricular function. It can be applied in clinical practice if the reproducibility of the technique is known so that imprecision can be minimised. Five normal echocardiograms of average clinical quality were selected and four cycles from each echocardiogram were digitized on two occasions by four different digitizers using an 'Apple II' computer. The study design allowed the sources of imprecision to be identified by analysis of variance. Assessment of the clinically most useful digitized measurement, peak rate of change of diastolic left ventricular dimension (dD/dt), was imprecise with a large within-subject variance and a 95% confidence interval of +/- 6.5 cm s-1; too wide for clinical use. The replication component accounted for 90% of this variance, with cycle to cycle and between-digitizer variance components being much less important. This large replication component will be reduced simply by repeating digitization; for dD/dt repeating digitization four times would theoretically reduce the confidence interval to a useful value of +/- 3.6 cm s-1. The 95% confidence interval for a single digitised measurement of diastolic left ventricular minor dimension was +/- 0.32 cm, for diastolic posterior wall thickness +/- 0.23 cm, and for the isovolumic relaxation time (A2-MVO) +/- 27 ms. Replication was again the largest component of variance so that the biggest improvement in precision will come from simply repeating digitization. Digitization on a cheap microcomputer system can provide clinically useful information provided reproducibility and sources of imprecision are known with clinical, as opposed to research, echocardiograms and conditions.

Adult↗
PubMed1979

Spatial firing patterns of auditory neuron network modelling by computer simulation.

This communication examines, in digital computer simulated network, input signals and response patterns established at excitatory neurons' level i.e. the membrane potential of neuron soma. It is restricted to spatial patterns of the auditory neuron networks and time factor for nervous conduction and transmission is neglected compared with long maintained membrane potentials of neuron somas. The model analyzes the change in the spatial patterns of the membrane potential in the two dimensional networks of the auditory system. In order to evaluate the contribution of the various parameters, it is started that the simplest model has only one parameter, lateral inhibition. The other parameters are then added, one at a time, to successive models. The lateral inhibition is a necessary condition in the auditory nervous system if any sharpening of the response areas in the single neurons is to occur. A necessary condition for the validity of the model is that is should be applicable to the other senses such as vision and chemical patterns, taste. The threshold feature of auditory neurons aids in producing a sharpening in the neuron of the auditory relay nuclei. It does this clipping the spatial response patterns in one dimensional arrays of excitatory neurons. Recurrent inhibition seems a necessary condition in the sensory nervous system that any kinds of input signals are to be preserved over a wide range of stimulus intensity. In other words, this network has a wide dynamic range against any kinds of input signals. A simple self-recurrent negative feedback does not contribute to the sharpening, but more complex socalled averaged type does. A neuron network is capable of responding stably to stimuli with a wide range of intensity and with any kind of spatial patterns if there is a simple negative feedback mechanism. When there is no negative feedback, input signals soon disappear or saturate in the neuron network. Therefore, recurrent inhibition is the most important mechanism. Spontaneous activity appears to aid in the sharpening by providing a kind of contrast, that is by reducting the amount of activity in neurons adjacent to the excitatory area. Moreover, the effect of spontaneous activity in the model seems to make repples around the excitatory area and suggests that an introduction of activity at any stage of the networks, from whatever source for example reticulum formation and thalamus, might appreciably alter the response patterns at subsequent neuron network. This suggests that the mechanism of the consciousness that might be controlled by the thalamus and or reticular formation. These two dimensional neuron networks may be expanded to three dimensional neuron networks. The former might simulate the auditory nervous system while the latter might simulate the visual system.

Animals↗
PubMed1977

Rapid and accurate determination of the median lethal dose (LD50) and its error with a small computer.

A program for a small digital computer was developed to calculate the median lethal dose (LD50) and its errors. The algorithm employed in the program was based on a method described by Bliss. Modifications introduced by Finney are also discussed. The results indicate a high degree of accuracy compared with calculations performed by Bliss. The accuracy and speed of calculation exceeded those possible with simplified and graphic methods. The data and results for four toxic compounds are presented.

Animals↗
PubMed1982

Efficient use of a digital oscilloscope-computer combination in the physiology laboratory.

This communication outlines a system that has been implemented to interface a digital oscilloscope with a general purpose digital computer. The computer chosen was the Digital Equipment Corporation PDP 11/34, the oscilloscope chosen was the Nicolet Explorer III. To illustrate the capabilities of this combination, two examples of data analysis from our cardiovascular research laboratory were included. The combination of the two devices yields a more powerful research tool, which allows data manipulation beyond the capabilities of the oscilloscope.

Animals↗
PubMed1985

Cardiac applications of digital subtraction angiography.

Recent developments in digital computer technology have enabled direct digital acquisition of radiographic images at spatial and temporal resolutions similar to that of cineradiography. Initially intended as a means of performing peripheral angiography, digital subtraction angiography has been increasingly applied to cardiac catheterization procedures. Advantages of cardiac digital subtraction angiography include the capabilities to: immediately replay, magnify and enhance angiographic studies during coronary artery interventions, perform left ventriculography with peripheral contrast injections and direct left ventriculography with substantially reduced contrast doses, perform bypass graft visualization using aortic root contrast injection, assess relative regional coronary blood flow and facilitate the quantification of ventriculographic and coronary stenosis parameters. Clinical comparisons of standard cineradiographic and digital angiographic studies have demonstrated very similar results.

Angiocardiography↗
PubMed1980

A computer system for the analysis and synthesis of field potentials.

It is shown how field potentials due to neuronal membrane processes can be computed by means of a digital computer system. The essence of the method consists in evaluating a discrete expression for the field potential as a function of membrane potentials. This expression is considered as a three-dimensional convolution. In the computer system this convolution is performed by multiplication in the spatial Fourier domain. Introduction of a density function provides the possibility of evaluating in an easy way the field potential of a population of neurons. To demonstrate the applicability of the system, field potentials of different membrane potential configurations in the brain have been computed.

Animals↗
PubMed1975

[Method for the continuous measurement of the phase relation between heart beat and respiration (author's transl)].

A simple method for the continuous analysis of the phase relation between heart beat and respiration is described. By means of an analog computer the timing of the R wave of the ECG within the respiratory cycle is graphically displayed. In contrast to other investigations, the onset of the inspiration is used as starting signal. The results obtained with the analog computer were completed by a digital computer program, which allowed in addition to calculate histograms of the events. In order to evaluate our method we used an analog model of two coupled oscillators. Responses obtained at different coupling characteristics were compared with measurements in four subjects. The results indicate a mutual interaction between heart action and respiration as cause of the coupling of these two systems.

Computers↗
PubMed1999

Quantification of cellular properties from external fields and resulting induced velocity: magnetic susceptibility.

An experimental technique is discussed in which the magnetic susceptibility of immunomagnetically labeled cells can be determined on a cell-by-cell basis. This technique is based on determining the magnetically induced velocity that an immunomagnetically labeled cell has in a well-defined magnetic energy gradient. This velocity is determined through the use of video recordings of microscopic images of cells moving in the magnetic energy gradient. These video images are then computer digitized and processed using a computer algorithm, cell tracking velocimetry, which allows larger numbers (>10(3)) of cells to be analyzed.

Cells, Cultured↗
PubMed1977

Some quantitative results on Golgi impregnated axons in rat visual cortex using a computer assisted video digitizer.

Axonal fiber distributions of pyramidal cells in the visual cortex of the albino rat have been investigated using the rapid Golgi method and modern data collecting techniques. Three dimensional coordinate information was extracted from Golgi-impregnated axonal networks using a computer-assisted video digitizer. Computer programs used this data to generate various statistical distributions. In particular, angular distributions of the initial collateral segments and their endpoints were examined and found to reveal anisotropies. Inspection of the spatial distributions of the endpoints indicated a clustering at two distinct levels with respect to the pyramidal cell from which they originate. Dynamic graphic displays of the three dimensional data have been obtained and presented in the form of computer tracings of various orthogonal projections.

Animals↗
PubMed1996

Analysis of nickel-titanium versus stainless steel instrumentation by means of direct digital imaging.

This study compared step-back preparations in curved canals using nickel-titanium (Ni-Ti) K-files and stainless steel K-files. Forty canals in mesial roots of mandibular molars were embedded in casting resin and cross-sectioned at three levels: 1 to 2 mm from the apical foramen, middle of the curve, and coronal. Direct digital computer images were recorded before and after instrumentation. Superimposition of the images combined with digital subtraction computer software allowed direct measurement of area instrumented, distance of transportation, and shape analysis. The computer software calculated absolute center of gravity for each image analyzed to get a full 360-degree interpretation of the canal transport. Time of instrumentation was recorded. Results showed Ni-Ti files to cause significantly less transportation and remain more centered at the apical level (p < 0.05). Area removed by Ni-Ti and stainless steel files was not significantly different (p < 0.05). Time of instrumentation was not significantly different for Ni-Ti and stainless steel instruments (p < 0.05). Cross-sectional shape of the instrumented canal was not significantly different (p < 0.05).

Dental Alloys↗
PubMed1997

Analysis of Ni-Ti versus stainless steel instrumentation in resin simulated canals.

This study compared step-back preparations in curved canals of resin blocks using nickel-titanium K-files and stainless steel K-files. Forty canals in resin blocks were cross-sectioned at 3 levels: 1 to 2 mm from the apical foramen, middle of the curve, and coronal. Direct digital computer images were recorded before and after instrumentation. Superimposition of the images combined with digital subtraction computer software allowed direct measurement of area instrumented, distance of transportation, and shape analysis. Time for instrumentation was recorded. Results showed Ni-Ti files to cause significantly less transportation and remain more centered at the apical level (p < 0.05). Area removed by instrumentation was significantly greater for stainless steel files at the middle level (p < 0.05). Cross-sectional shape of the instrumented canal was not significantly different (p < 0.05). It took significantly longer to prepare a canal with Ni-Ti K-files in resin blocks compared to stainless steel (p < 0.05). Resin simulated canals showed similar results compared to canals in extracted roots using an identical methodology.

Analysis of Variance↗