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Results for “Analog-Digital Conversion”

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At least 37 records · Page 2Linked to original sources
PubMed1979

Comparison of interwave latencies of brain stem auditory evoked responses in narcoleptics, primary insomniacs and normal controls.

A study of brain stem auditory evoked responses (BAER) was carried out in 10 narcoleptics, 10 primary insomniacs and 10 normal controls to determine if a neurophysiologic abnormality could be detected in these primary sleep disorders. The mean interpeak conduction times of Wave I-III, III-V and Iv were compared between the following groups: normal controls awake and in monitored sleep; narcoleptics awake and in monitored sleep, normal controls awake and narcoleptics awake; normal controls awake and insomniacs awake; narcoleptics awake and insomniacs awake; narcoleptics with cataplexy (n = 6) awake and narcoleptics without cataplexy (n = 4) awake. No significant differences were found which suggests that these sleep disorders represent dysfunctions which do not involve brain stem structures subserving the BAER.

Adult↗
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↗
PubMed1979

Computer-monitored radionuclide tracking of three-dimensional mandibular movements. Part I: theoretical approach.

A new technique for the three-dimensional recording of a person's mandibular movement is described. A small and harmless radioactive source is fixed on the patient's skin at the point of interest or sealed in a tooth cavity. Using the proper collimation, the motion of the point source is recorded via a gamma camera and minicomputer. Long-term storage on a magnetic device offers playback, slow motion facilities, and data analysis through the use of sophisticated computer languages. Simultaneous recordings using two cameras, or postsynchronization of two different views of an experiment, enable the three-dimensional restitution of mandibular movements. Superimposition of a grid of radioactive spots spaced at measured intervals during the recording permits a straightforward calibration of the patient's motion. Multiple sources in a single experiment may be recorded to describe the displacement of several points of interest. This method, derived from nuclear medicine techniques, offers a powerful tool of general interest for the tracking of dynamic events in many fields of dentistry such as temporomandibular joint dysfunction and prosthetic restorative techniques. Further considerations on our experimental settings and results will be published in part II.

Analog-Digital Conversion↗
PubMed1977

Camera-computer systems for rapid dynamic imaging studies.

The extraction of valuable diagnostic information from rapid, dynamic studies performed on a gamma camera requires that the data be recorded for latter analysis. If these data are to be available rapidly and if quantitative analysis is to be performed, it is imperative that a computer be used in conjuction with the gamma camera. This review describes the more important features of a nuclear medicine computer system both from the point of view of hardware and software. The various aspects that cause some limitations to be imposed on the capability of the system in order to carry out fast, dynamic studies are described and some possible solutions are suggested.

Analog-Digital Conversion↗
PubMed1978

The measurement of distortion: mathematical considerations.

The proposed method for accurately determining the coordinates of given points in a three-dimensional space, along with the mathematical rigid body displacements to move these points into some predefined reference position, builds a complete model of the positional relationships of these points. On this basis additional information can easily be extracted, e.g., the distance between any two given points or the angle in degrees between any two given points or the angle in degrees between any three given points. An important advantage of the procedure is that the normally tedious calculations involved with distortions have been computerized, thus eliminating the tedium of repeated calculations. The possibility of calculation error is also reduced. Perhaps the greatest advantage to the investigator arises from the fact that once the procedural routine has been established and the computer programs written, the entire procedure can be done by technical personnel and does not necessarily require a large time committment from the principal researcher. Also, because of the normally small amount of time needed to read the coordinates and compute the inherent distortions, a set of computed distortions which appear unreasonable may be checked by repeating the entire set of coordinate readings and distortion calculations in a relatively short time.

Analog-Digital Conversion↗
PubMed1978

Quantification of vestibular nystagmus by an interactive computer program.

An interactive program for the analysis of nystagmus is presented, and some results obtained by processing postrotational responses are reported. The program is provided with a special subroutine which gives a quantification of the rhythm and regularity of the response through the histograms of the ratios between the duration of successive intersaccadic intervals and between the amplitudes of successive fast components. The consideration of these histograms has been proved to be highly significant in discriminating between normal and pathological responses.

Analog-Digital Conversion↗
PubMed1977

Sampling rates required for digital recording of intracellular and extracellular cardiac potentials.

Electrocardiograms and cardiac electrograms now frequently are measured for both clinical and experimental purposes by direct digital sampling, with no recording of the signal in analog form. This study examined the question of what sampling rates were required to measure accurately the continuous waveforms from the digital samples. Body surface waveforms and intracellular and extracellular waveforms measured directly from cardiac tissues were evaluated. Cardiac measurements included waveforms from the atrium, ventricle, atrioventricular transmission system and individual Purkinje strands. Sampling rates as high as 15,000 samples/sec were required to record accurately extracellular waveforms of the ventricular conduction system. Decreasing sampling rates were required as the recording site shifted through the ventricle to the body surface, where sampling rates as high as 1500 samples/sec were necessary.

Action Potentials↗
PubMed1979

Pulmonary vascular impedance analysis of adaptation to chronically elevated blood flow in the awake dog.

Pulsatile pulmonary hemodynamics were analyzed in a chronic awake canine high flow model. Standard mean flow and pulsatile flow hemodynamics were measured and alterations in the proximal pulmonary vascular physical properties were quantified by the characteristic impedance (Zo). Pulmonary vascular resistance (PVR), which assesses arteriolar-capillary recruitment of perfusing radius and measures a more distal pulmonary vascular response to changing flows, also was calculated. Twelve control dogs were studied and had mean Qpa (pulmonary blood flow) = 2.02 +/- 0.15 liters/min, Zo = 193 +/- 20 dyne sec cm-5 and PVR = 416 +/- 32 dyne sec cm-5. Ten dogs were studied awake 20 weeks after creation of bilateral arteriovenous fistulae. Five of these shunted dogs, designated group A, developed Qpa = 3-4 liters/min (mean = 3.80 +/- 0.09, P less than 0.001 different from control group); the other five dogs (group B) developed Qpa = 4-8 liters/min (mean = 5.87 +/- 0.16, P less than 0.001). In group A, Zo = 143 +/- 8 (P less than 0.05) and PVR = 249 +/- 6 (P less than 0.10). In group B, Zo = 90 +/- 5 (P less than 0.005) and PVR = 126 +/- 14 (P less than 0.01). The total input power (potential and kinetic) was 125% above the controls for group A (P less than 0.001) and 264% for group B (P less than 0.001), but the mean energy components increased significantly more than did the pulsatile components. These data demonstrate a lower impedance to pulsatile flow during chronically elevated total flow which effects a reduction in both the work load of the right ventricle and the transmission of energy to the precapillary bed. Analysis of the alterations in characteristic impedance suggests a distinct proximal pulmonary vascular mechanism of decreased vessel stiffness (decreased elastic moduli) for adaptation to chronically elevated flow loads which is in addition to the two geometric alterations of proximal arterial dilation and distal vascular channel recruitment.

Analog-Digital Conversion↗
PubMedDate not supplied

Low-frequency harmonic acceleration as a test of labyrinthine function: basic methods and illustrative cases.

These preliminary findings reveal that low-frequency harmonic acceleration can be used to detect unilateral peripheral deficits that agree with caloric findings. However, the responses to sinusoidal acceleration are less variable than the caloric responses and allow one to more closely evaluate changes in pathology with time. Therefore, it appears that harmonic acceleration provides additional information that is useful in confirming other test results and that a complete otoneurologic evaluation should include this type of rotational testing.

Adult↗
PubMed1975

[Computer analysis of ventricular pressure recordings: evaluation of myocardial contractility on the dog heart in situ].

The contractile indices Vmax (maximum shortening velocity of the contractile element) and ARPD (power averaged rate of power density generation) which have been shown to be unaffected by alterations in preload and afterload were computed from isovolumic left ventricular pressure data of dogs. The two indices were tested for their ability to detect changes in contractility induced by a positive inotropic drug (Isoprenalin). Whereas a good correlation was found between ARPD and Vmax (coefficient of correlation 0,895) the index ARPD was more sensitive to augmentation of myocardial contractility; also because it is simpler to obtain computationally and more appropriate for the intact heart from a theoretical point of view. ARPD should be useful especially for quantification of acute changes in myocardial contractility.

Analog-Digital Conversion↗
PubMed1975

[Computerized axial tomography of the skull - diagnostic possibilities and clinical results (author's transl)].

Computerized axial tomography is a new method of tissue examination with x-rays whereby a picture can be produced which is a representation of a slice of the skull. This is done by irradiating the skull from 180 or 225 incremental angles and measuring the absorption at each of these angles. Then with the aid of a computer a tomogram is produced which can be displayed on a screen. These tomograms are representations of a cross-section of the skull composed of 160 X 160 points showing the various intracranial structures with great detail. The present study demonstrates the diagnostic possibilities of the high definition matrix with reference to brain disorders in a large sample of patients for the first time. Some tumours are shown as areas of decreased absorption compared with normal brain tissue. Others, however, have been found to have higher absorption values. With glioblastomas very contrasting pictures are produced with coexistng areas of decreased, increased and similar values to brain tissue. The most important finding is the visualization of brain oedema which appears as a low density area. A grading system of brain oedemas is proposed. The brain oedema associated with tumours has been found to propagate mainly in the white matter producing finger-like shapes. Out of 209 intracranial tumours 203 were recognized in the plain scan, a further five after contrast enhancement. In patients who have suffered from a stroke the differentiation between haemorrhage and infarction is made simple due to the contrasting appearance between the two types of lesion. Location, size and propagation direction of a haematoma as well as rupture of a haemorrhage into the ventricular system can be defined exactly. With brain infarction the hypoxically damaged tissue is well delineated and readily attributable to a given vascular area. In head injuries, for the first time it is possible to differentiate brain contusion with oedema from intracerebral haematoma. Coup and contre-coup are demonstrated. All types of acute intracranial haematomas may be diagnosed easily. With chronic subdural haematomas the new method fails if the contents of the haematoma shows the same absorption values as brain tissue. Late sequelae of head trauma such as contusion defects and necrosis of tissue after oedema can be seen in the tomogram. With infantile hydrocephalus, subdural effusions and malformations of the brain, computerized axial tomography offers a complete diagnosis so that other invasive, neuroradiological investigations may be avoided. Orbital tumors are picked out with great clarity. The high definition matrix allows the demonstration of the optic nerve, the lense and the suspension of the eyeball. Without doubt in the coming years computerized axial tomography will play a dominant role in the diagnosis of brain disorders.

Absorption↗
PubMed1978

Computerization of three-channel thrombelastograph.

A small-size and low-cost microcomputer using an Intel 8080 micro-processer is employed to provide real-time data collection and reduction of a three-channel electronic-readout thrombelastograph (TEG). Computed values of significant clotting parameters are obtained instantly allowing for rapid analysis and monitoring of many patients. Computer hardware was designed to optimize signal sampling rates, processing time and storage.

Analog-Digital Conversion↗
PubMed1977

[Automatic analysis of gastrographies by means of optical digital equipment (author's transl)].

The present paper is concerned with problems of automatic analysis of radiograms, specially cinegastrographies. This study is connected with the utilisation of an interactive system including optical digitizer with its units of control and visualization. This system can explore the radiologic film in its current size of 30 X 40 cm. The particular interest of this application is extracting several parameters characterizing the size and the shape of the stomach. A middle axis can be extracted by computing, from this one a spatio-temporal diagram can be obtained. From this methodology of representation, several states of gastric motility could be characterized.

Analog-Digital Conversion↗