Showing papers on "Artifact (error) published in 1979"

Heartbeat detection and artifact discrimination method and apparatus

Abstract: Apparatus for discriminating between heartbeat and artifact information contained in an ECG signal includes a pair of difference amplifiers, level-detecting circuitry and a coincidence detector. ECG waveforms are obtained from a number of heartbeat-sensing transducers attached to a person. The waveforms are individually applied to a pair of difference amplifiers to produce difference signals containing heartbeat information. The difference signals are applied to level-detecting circuits and compared to predetermined voltage levels to identify particular peaks indicative of a heartbeat. The result of the level-detecting circuits are compared for time coincidence to produce an output pulse indicative of a heartbeat.

Respiration monitoring method and apparatus including cardio-vascular artifact detection

Abstract: A respiration monitor for measuring the variations of the thorax impedance of a patient due to respiration is described The monitor includes circuitry for suppressing the indication of unwanted signals caused by cardio-vascular activity of the patient The circuitry receives trigger signals immediately following the QRS complex of the patient's ECG waveform If a certain negative-going slope is detected in the thorax impedance waveform following the QRS complex, it is counted as a cardio-vascular artifact and not respiration activity After a predetermined number of cardio-vascular artifact are detected and counted, the respiration monitor is disabled so that this cardio-vascular activity will not reset an apnea counter

Expectancy Effects of Labels: Fact or Artifact?:

Abstract: Sociological deviance theory (Becker, 1963) has been a significant, but frequently unrecognized, influence on recent discussions in special education. Deviance theory suggests that labels cause changes in the expectancies of significant persons in the social system. The label and associated expectancies are believed to be the basis for a deviant status which in turn is communicated to the person, incorporated in the belief system of the person, and then reflected both in the behavior of the labeled person and the behaviors of others in the social system toward that person. In short, labels create self fulfilling prophecies (Erikson, 1962) and maladaptive or deviant behavior is allegedly caused by negative labels.

Incoherent image addition and subtraction: a technique.

Abstract: A technique of incoherent image addition and subtraction is described. The basic advantage of this technique is its use of white light processing, in which case the unavoidable artifact noise in the coherent optical processor may be removed. Although the incoherent processing technique that we have proposed is effective only in a 1-D operation, it also works for 2-D image addition and subtraction.

Filtering of Muscle Artifact from the Electroencephalogram

Abstract: When recorded by surface electrodes, the electroencephalogram (EEG) may contain unwanted signals due to depolarization of scalp muscles and various electrochemical effects at the surface-metal junction. The former artifacts, in particular, are difficult to remove by linear filtering. This design study indicates that a state-of-the-art non-linear filter which includes a matched-filter detector with likelihood-ratio decision logic can give significant performance improvement over a third-order linear low-pass filter typical of existing equipment. The same approach can be applied to related electrophysiological filtering problems.

Ultrasonic pseudolesions of the liver.

Abstract: Several common and/or misleading hepatic sonographic pseudolesions which may closely simulate pathological conditions are presented. All were caused by anatomical variants or scanning artifacts. Care should be taken to avoid mistaking such findings for true liver disease.

Pacemaker monitoring recorder

Abstract: A recorder for monitoring the operation of a cardiac pacemaker and the response of the patient to the pacemaker includes a recorder module which receives a composite signal including an ECG signal, a pacemaker spike having a frequency spectrum that lies substantially at frequencies greater than the frequency band required to pass the ECG signal, and further includes artifact noise within the frequency spectrum of the pacemaker spike. The recorder module distinguishes the pacemaker spike from the artifact noise and upon recognizing the pacemaker spike, the recorder module produces a distinctive synthesized signal whose frequency spectrum lies substantially within the frequency band required to pass the ECG signal so that the synthesized signal will pass through the pre-emphasis filter that is used to reject artifact noise and will then be recorded.

Response : Brain Stimulation Reinforcement: Implications of an Electrode Artifact

Abstract: employed as described (3). 6. A similar result has been reported in rabbit superior cervical ganglion by H. Kobayashi and B. Libet, [J. Physiol. (London) 208, 353 (1970)]. In our experiments, membrane resistance was measured by using hyperpolarizing current pulses (-100 pA, 30 to 60 msec). Changes in input resistance as small as 10 percent were detectable. 7. D. Geduldig and D. Junge, J. Physiol. (London) 199, 347 (1968); M. Klein and E. R. Kandel, Proc. Natl. Acad. Sci. U.S.A. 75, 3512 (1978). 8. M. P. Blaustein, J. Pharmacol. Exp. Ther. 196, 80 (1976). 9. S. Minota and K. Koketsu, Jpn. J. Physiol. 27, 353 (1977). 10. K. Dunlap and G. D. Fishbach, Soc. Neurosci. Abstr. 4, 443 (1978). 11. C. Van Breemen, B. R. Farinas, R. Casteels, P. Gerba, F. Wuytack, R. Deth, Philos. Trans. R. Soc. London Ser. B 265, 57 (1973). 12. P. G. Kostyuk and D. A. Krishtal, J. Physiol. (London) 270, 569 (1978). 13. A. S. Marrazzi, J. Pharmacol. Exp. Ther. 65, 395 (1939); E. Bulbring, J. Physiol. (London) 103, 55 (1944). 14. D. D. Christ and S. Nishi, J. Physiol. (London) 213, 107 (1971); N. Dun and S. Nishi, ibid. 239, 155 (1974). 15. We thank P. J. Yarowsky for helpful discussions and L. Worth for assistance in preparing the manuscript. Supported by NIH gant NS-05820 and a Scottish Rite schizophrenia fellowship to J.P.H. who was on leave from the Department of Physiology and Biophysics, University of Miami School of Medicine when this research was perforned.

Ciassification of Artifacts in X-Ray Cr Images Due to Nonlinear Shadows

Abstract: Polychromaticity and noise artifacts in computed x-ray tomography can be traced to a nonlinear dependence of projection data and its variance upon an ideal consistent set of projection data. We describe both types of artifacts and present mathematical models. A comparison is made between artifacts in the image i(r) of CT values and artifacts in the distribution ?2(r) of the noise variance. Three classification schemes for these nonlinear artifacts are presented: the physical origin of the artifacts (I), the geometrical appearance of the artifact (II), and the degree of consistency of the nonlinear shadow (III).

Information And Artifact In Second-Order Statistics From Computed Tomography (CT) Images

Abstract: In conventional computed tomography images, only the average CT number, which is a first-order statistical parameter, is used to characterize the tissues by giving an estimate of tissue density. Second-order statistical parameters such as the signal variance and cross-correlation function have also been used to obtain additional information to discriminate between certain tissues and lesions. However, the contribution of quantum noise to the signal variance and cross-correlation function creates, for the conventional CT patient dose, a background signal often larger than the signal containing the information about tissue structure. The misleading information, called "artifacts," in second-order image statistics caused by quantum noise is studied. The distribution of the contribution of quantum noise to second-order statistical parameters is object-dependent, space dependent, and "nonlocal." The term "nonlocal" refers to the wide-ranging effects of nonlinear artifacts on the distribution of second-order statistical parameters. We present an analysis and examples of some of the artifacts encountered and also comment on how these artifacts affect the potential of these parameters for clinical use, such as tissue characterization.

Estrogens and increased endometrial cancer: fact or artifact?

Abstract: The first case-control studies that dem onstrated a strong association between replacement estrogens and endometrial cancer were published in December 1975.1,2Further data supporting the as sociation appeared in June 1976.@ More recently, Jick et al4 published the results of a study based on the experience of Group Health Cooperative of Puget Sound (GHC), a health maintenance or ganization that provides virtually com plete prepaid medical coverage for out patient care, drugs, and hospital services. Carefully documented computerized rec ords of prescriptions ifiled and of hos pital diagnoses have been maintained at GHC since July 1975. From these rec ords, together with interviews with pa tients who had endometrial cancer and with appropriate controls, it was possible to estimate the risks of developing endo metrial cancer for current users and non users of replacement estrogens over a 24-month period from July 1975 to June 1977. The annual incidence rate among current estrogen users (with intact uteri) was one to three percent. For non-users, it was consistently about 0.1 percent. The vast majority of the cases of endometrial cancer among estrogen users occurred in women who had taken the drug for at least five years. Further evaluation of the data showed that there was a dramatic drop in estrogen use at GHC following the initial reports of an association be tween this drug and endometrial cancer in 19751,2 Six months later there was an equally dramatic drop in the incidence of endometrial cancer. These data suggest that the changes induced by long-term estrogen exposure in the development of endometrial cancer are stopped or re versed shortly after the drug is discon tinued. The fall in incidence at GHC came after several years of rising incidence there4 and is part of a substantial decline that occurred in the United States from 1975 to 1977, especially in the West.4 Indeed, the fall in incidence of endo metrial cancer was estimated to be over 40 percent between 1975 and 1977 in the western United States—an area that pre viously had had the highest rate of both estrogen use and endometrial cancer in the country.4 An alternate explanation to that mentioned above is that discon tinuation of estrogen postpones the time of diagnosis. Continued monitoring of this population, as well as nationwide statistics, will determine which explana tion is correct.

An unusual ECG artifact--results of a faulty recorder.

Abstract: To the Editor.— Accurate interpretation of an ECG requires that it is free from distortion and artifact. However, with the increasing use of monitoring devices, ECG artifacts are on the increase and, in a recent survey, were found to be present in as many as 58% of all tracings.1Most of these were due to poor techniques and can be easily recognized by an experienced and attentive interpreter. Artifacts from malfunctioning equipment, although uncommon, are known to occur and may lead to serious diagnostic consequences.2I was recently confronted with an unusual ECG, which was subsequently found to be the result of an instrument-related defect. Report of a Case.— The patient was a 36-year-old man in whom shortness of breath and pleuritic retrosternal and right-sided chest pain developed. He was known to have a case of malignant pleural mesothelioma of the right side of the chest and had

Siderocapsa Major-- Fact or Artifact?

Abstract: • • • • LIST OF FIGURES AND TABLES •

Backward conditioning: An artifact of experimental design?

Abstract: Various interpretations of the nature of backward conditioning are briefly considered. After reviewing the three major interpretations of backward conditioning, another possible explanation is offered. It is suggested that backward conditioning may actually be long-trace forward conditioning, with the CS of one pair serving as the CS for the next UCS.