Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “COMPUTERS, DIGITAL”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 631 records · Page 35Linked to original sources
PubMed1977

A new display technique for computer-processed digital scans.

This article presents a new approach for presenting scintigraphic images. The technique combines the conventional plotting the contour lines and the highlighting, by means of hatching, of the concavities (or convexities) of the 'surface' representative of radioactive distribution. The search for the surface features is achieved generally by the method of normal curvatures. An example with a phantom demonstrates the utility of this representation method.

Computers↗
PubMed1986

Reconstruction of electrocardiogram using ionic current models for heart muscles.

A digital computer model is presented for the simulation of the electrocardiogram during ventricular activation and repolarization (QRS-T waves). The part of the ventricular septum and the left ventricular free wall of the heart are represented by a two dimensional array of 730 homogeneous functional units. Ionic currents models are used to determine the spatial distribution of the electrical activities of these units at each instant of time during simulated cardiac cycle. In order to reconstruct the electrocardiogram, the model is expanded three-dimensionally with equipotential assumption along the third axis and then the surface potentials are calculated using solid angle method. Our digital computer model can be used to improve the understanding of the relationship between body surface potentials and intracellular electrical events.

Computer Simulation↗
PubMed2001

Enhanced cardiac thermal dilution measurement of cardiac output, volumes, regurgitation, valve effective diameters, ventricular power and efficiency -- Feasibility analysis using digital simulation.

Cardiac output is measured by the thermal dilution method which uses a quadruple lumen catheter, with a thermistor on the tip, through the right atrium, right ventricle and into the pulmonary artery. Cold saline is injected into the right atrium and the resulting pulmonary artery temperature profile is integrated. The same procedure performed with three thermistors and three pressure sensors located on the catheter to measure temperature and pressure in the atrium, ventricle and artery respectively will produce a set of temperature and pressure curves with shapes determined by injectate temperature, injectate volume, heart rate, systolic time interval, body temperature, cardiac output, volumes, flow rates and valve openings. A digital computer program has been developed to optimize the fit of a lumped parameter model to the thermodilution curves in order to determine heart rate, systolic time as a fraction of cardiac cycle, right atrial systolic and diastolic volumes, ventricular systolic and diastolic volumes, cardiac output, inflow valve forward and reverse flow rates and effective diameters, outflow valve forward and reverse flow rates and effective diameters, ventricular power and efficiency. The program has been tested over a range of operating conditions including noise in the temperature and pressure signals, randomly varying heart rate and cardiac cycle. All of the data for the tests were produced by a digital computer simulation of a pulsatile artificial heart. The results of these tests indicate that the enhanced thermal dilution analysis method is feasible.

Cardiac Output↗
PubMed1977

The measurement of distortion: theoretical considerations.

When very find measurements are recorded for the purpose of establishing distortion values, from the standpoint of accuracy, specific procedures must be developed. In the procedural system defined here, a potential major source of error is indicated and the means of overcoming this error established. From the standpoint of modern electronic technology, the use of an analogue-to-digital interface with a digital computer is considered extremely advantageous and allows the utilization of technical help to carry out the preliminary measurements. Under these circumstances, major error sources, such as reader error and calculation error, are eliminated. Further, multiple readings on each point can be made without significant sacrifice of time. This latter statement can help define the reading accuracy on each point and allows an immediate further set of readings on any point that has a large variation in the initially established set of readings. The applicability of this approach to any system in which an accurate set of readings is required to define distortion or some other parameter is limited only by the imagination of the investigator. Measuring points can be established at any desired location, and the number required is a function of the mathematical analysis being attempted. The use of a digital computer to compute the final values allows an immediate remeasurement of the initial values if necessary, since the computer response time is of the order of seconds for the calculations carried out. This is very important if changes in the experimental setup are likely to occur with time. In general, a computerized scheme such as is proposed here allows the investigator to concentrate on the experiment rather than the calculation of results. Also, the use of technical help to carry out delicate measuring procedures can allow the investigator more time to analyze the final results.

Analog-Digital Conversion↗
PubMed1988

[Value of computer-assisted, digital long-term ECG analysis in clinical routine practice].

At present the Holter method (HM) is a frequently used investigational procedure in the clinical routine. It was the aim of a prospective study to evaluate the HM from the user's point of view. Therefore a questionnaire was attached to each analysis report including two main questions, which should be answered by the referring physician: Does the analysis result fulfill the consumer's needs? What consequences are drawn due to the HM results? Among 675 questionnaires returned to the laboratory 75% of the referring physicians felt satisfied by the HM result. Disappointments were predominantly related to too infrequently occurring episodes, which did not appear during one 24-hour recording period. Evaluation of therapy (89%), recording prior to antiarrhythmic therapy (84%) and quantification of well-known arrhythmias were the most successful indications of HM. The tremendous daily variability of infrequent symptoms or arrhythmias were the main causes for unsatisfactory results. A successful HM led predominantly to therapeutic consequences (begin, continuation, change or withdrawal of anti-arrhythmic drugs). In 25% HM was not followed by further therapeutic or diagnostic consequences, so that the indication for the HM should be reevaluated! Diagnostic consequences included repeated HM, ECG-Telephone-Transmission consequences heart catheterisation or electrophysiological procedures. In summary the Holter method satisfies the physician's demands if the expectations do not exceed the limitations of the method.

Adolescent↗
PubMedDate not supplied

Varied morphology of spontaneous single muscle fiber discharges.

Fibrillation potentials and positive sharp waves have rather stereotypical morphologies generally conforming to a triphasic initially positive and biphasic initially positive waveform, respectively. Careful attention during the needle electromyographic examination of muscle tissue with unstable resting membrane potentials, however, frequently reveals spontaneous potentials with appearances conforming to not only those described above but also waveforms with morphologies that can best be characterized as a blend of both a fibrillation potential and positive sharp wave. These "hybrid" or composite waveforms are hypothesized to arise from an electrical summation of two single muscle fibers repetitively discharging in a time-locked manner. Five individuals with lower motor neuron disorders displaying spontaneous discharges at rest during the needle electromyographic were examined. The spontaneous discharges were categorized according to their morphology. Stereotypical positive and negative onset fibrillation potentials and positive sharp waves from these patients were digitized. Computer simulations summating the digitized waveforms were successful in reproducing all of the observed "hybrid" waveforms documented in the patients. The supposition of two single muscle fibers discharging within a temporal domain conducive to electrical summation is an extension of the concept that electrical summation of muscle fibers comprising a motor unit summate to generate an electrical representation of that motor unit.

Adult↗
PubMed1988

Mathematical analysis of computed carpal models.

The computed carpal models from digital computed tomography (CT) data obtained in this study compare favorably to natural anatomy. A new application of algebraic analysis of this data provides mathematical markers from which to calculate the position and orientation of each carpal bone. When the origin of the spatial coordinates of a carpal bone is transferred to the centroid of the bone, the data can be treated as three-dimensional pattern vectors describing its surface. It is then possible to calculate vectors that are the principal axes of the geometry. These axes provided references that were used to calculate position and orientation of the carpal bones in three wrist specimens. Comparisons of volumes, surface areas, and sizes and proportions of five computed images of each carpal bone from two of these wrists demonstrate the reliability of the technique. The analysis of CT scans of ceramics with known boundaries allows an estimation of its accuracy. The technique is well suited to the future study of normal wrist kinematics and pathological conditions.

Carpal Bones↗
PubMed2002

Temperature controller for thermal ionization mass spectrometry.

We describe the use of a simple voltage stabilizer that controls the filament temperature (T(f)) in the ion source of a thermal ionization mass spectrometer. The filament voltage (V(f)) is measured by means of a separate pair of wires connected inside of the ion source in parallel to the wires supplying power. It has been demonstrated that V(f) is directly proportional to T(f) in a wide range of filament temperature. The T(f) value is solely controlled by the reference voltage (V(r)) that can be manually selected from a voltage divider or by means of a computer. Digital signals from the computer in the form of a series of pulses are transmitted opto-electronically and subsequently converted to analog signals. The temperature controller described here was successfully applied for analysis of potassium concentration by the isotope dilution method.

Journal Article↗
PubMed1983

Pulmonary mechanics in conscious Fischer 344 rats: multiple evaluations using nonsurgical techniques.

An adaptation of the method reported by Amdur and Mead (1958, Amer. J. Physiol. 192, 364-368) was used to evaluate pulmonary mechanics in conscious rats, utilizing a flow plethysmograph and intraesophageal catheter to determine compliance, resistance, respiratory flow, thoracic pressure, tidal volume, frequency, and minute volume. The procedure did not require surgery, and repeat evaluations were made in conscious rats. Real time calculations of pulmonary parameters were accomplished with an analog computer interfaced with a digital computer for display and data storage. Multiple evaluations (1, 3, 6, 13, 18, 24, 30, and 36 weeks) in 40 rats are reported. The utility of the system in establishing a base line against which pulmonary impairment, related to the effects of known pulmonary toxicants, e.g., ANTU and NO2, could be measured, was evaluated.

Aging↗
PubMed1999

Finding paths in a labyrinth based on reaction-diffusion media.

During the past few decades, many proposals were made on how to take an effective solution for finding a path in a labyrinth, one of the most well known problems of high computational complexity inherent in information processing by biomolecular and biological entities. In particular, attempts were made to use a technique attractive enough for solving this problem based on wave processes in reaction-diffusion media. Trigger waves in reaction diffusion systems spread simultaneously through all paths of the labyrinth in a highly parallel mode. Regretfully, the velocity of these waves is extremely low which gave no way for the practical implementation of this technique until now. An effective 'hardware' system was designed which was capable of finding a path in a labyrinth using fast phase waves. Three principal points were assumed as a basis for this design, i.e. (1) hybrid architecture that combined an information processing reaction-diffusion medium which performs operations of high computational complexity with a digital computer carrying out supplementary image processing operations; (2) light-sensitive information processing media of Belousov-Zhabotinsky type that enables the simulation of the labyrinth and spreading wave evolution by their images stored in the medium and reduces the problem to the image processing operations; (3) fast light-induced phase wave processes that spreads through the labyrinth in several seconds instead of hours which is typical for trigger waves inherent in reaction-diffusion media. These fundamentals along with the additional procedure of testing for labyrinth fragment connectness provided us with the opportunity to solve labyrinth problems.

Computer Simulation↗
PubMed2000

Comparison of landmark identification in traditional versus computer-aided digital cephalometry.

The aim of this study was to assess landmark identification on digital images in comparison with those obtained from original radiographs. Ten cephalometric radiographs were selected randomly. Seven orthodontic residents identified 19 cephalometric landmarks on both the original radiographs and the digital images. To assess the concordance between landmarks identified on the original radiographs and on their digital counterparts, the x, y coordinates for each landmark in the 2 modalities were transformed with the identical references. The placement differences for 19 landmarks between 2 methods were calculated and their components in horizontal and vertical directions were analyzed respectively. Multivariate analysis of variance showed that the "cephalometric radiograph" and "landmark" variation had greater influence than that from "method" (landmark identification on digital / original radiograph). It was also noted that the differences of landmark identification between original radiographs and their digital counterparts were statistically significant. The landmarks with significant differences of horizontal component on the x-axis were Me, Gn, ANS, PNS, LIA. The differences were generally under 1 mm with the exception of Or, Me, PNS, LIA. The landmarks with significant differences of vertical component on the y-axis were Po, Or, Gn. The inter-observer error for each landmark in digital images was generally larger than that in the original radiographs. However, statistically significant differences of inter-observer errors between 2 modalities were only found for 4 of the 19 landmarks. These 4 landmarks, Po, Ar, ANS, and UM, should be scrutinized more carefully during potential applications of digital cephalometry.

Analysis of Variance↗
PubMedDate not supplied

The origins of informatics.

This article summarizes the origins of informatics, which is based on the science, engineering, and technology of computer hardware, software, and communications. In just four decades, from the 1950s to the 1990s, computer technology has progressed from slow, first-generation vacuum tubes, through the invention of the transistor and its incorporation into microprocessor chips, and ultimately, to fast, fourth-generation very-large-scale-integrated silicon chips. Programming has undergone a parallel transformation, from cumbersome, first-generation, machine languages to efficient, fourth-generation application-oriented languages. Communication has evolved from simple copper wires to complex fiberoptic cables in computer-linked networks. The digital computer has profound implications for the development and practice of clinical medicine.

Computer Communication Networks↗