Showing papers on "Artifact (error) published in 1982"

Correction of EOG artifacts in event-related potentials of the EEG: aspects of reliability and validity.

Abstract: Correction of EOG artifacts using a regression approach is evaluated in terms of reliability and validity. Transmission rates are estimated for eight EEG channels in 67 subjects. The trimmed group means of these rates are shown to provide reliable measures. Eye artifact correction based on these group means is superior to the conventional rejection in terms of reducing correlation between EOG and EEG.

Systems and methods for processing physiological signals

Abstract: Systems and methods are disclosd for detecting the recurrence of physiological functions. The disclosed systems and methods are especially adapted for detecting the recurrence of a patient's respiration from a signal representative of changes in the patient's thoracic volume, despite the presence of cardiovascular artifact in the signal. A cardiovascular artifact filter suppresses the artifacts in response to a signal, generated by a cardiotachometer, which varies as and is proportional to the fundamental frequency of each artifact.

Artifact detector for heartbeat rate measuring system

Abstract: A heartbeat rate measuring system for monitoring a patient's EKG signal and estimating heartbeat rate. The system includes an artifact detection apparatus for filtering the EKG signal to detect the occurrence of a heartbeat artifact, and for inhibiting the measuring heartbeat intervals whenever an artifact is detected. The system therefore estimates heartbeat rate based solely on measurements of time intervals between actual heartbeats.

Removal of streaking artifact in computed tomography.

Abstract: In transmission computed tomography, relative X-ray attenuation measurements are made at various angles around a patient's body. These input projection data are reconstructed to yield a cross-sectional view of internal structure. If the body section contains material that severely attenuates the X-ray beam (e.g., surgical clips, lead fragments), high-density streaks that obliterate internal structure will be produced in the process of image reconstruction. This loss of diagnostic information renders the scan useless. A technique has been developed that removes this imaging artifact. The approach views the affected projection data as misinformation. These data are assigned new values, and image reconstruction is performed without changing existing computer hardware or software. Projection data for a head section containing a lead fragment were obtained by Monte Carlo simulation. Three methods of obtaining replacement data were examined. A nearest-neighbor pattern recognition technique yielded excellent results.

Pacemaker Spike Alternans: An Artifact of Digital Signal Processing

Abstract: Marked variability in the amplitude or polarity of pacemaker artifacts may be a clue to generator malfunction or partial electrode fracture. We report a case where "pacemaker spike alternans" occurred factitiously as a result of a digital "roll-over" effect. The widespread introduction of digital electrocardiographs into clinical practice makes recognition of such artifacts important.

Artifact patterns in multiple scanning beam radiography

Abstract: A limitation of the use of multiple scanning beams for scatter reduction in radiography is the possible creation of artifactual aperture patterns which can be caused: (1) by a synchronization between the pattern scanning frequency and the radiation waveform ripple frequency, or (2) by the fractional overlap of the scanning beams during the final beam pass. An analysis of the stages of artifact formation and the implications for various scanning beam approaches is presented.

Retrocaval pseudolymphoma: clinical impact of the mirror artifact.

Abstract: Figure 1. A (above), longitudinal section through the inferior vena cava (IVC). Note the echo-free mirror image (M) behind the IVC. (l: liver; PV: portal vein; D: d iaphragm.) B (below), subcostal transverse section through the liver. (RPV: right portal vein; RHV: right hepatic vein.) nomenon, which can be explained by almost total sound reflection, becomes particularly apparent when intrahepatic lesions located close to the diaphragm are mirror-imaged above the diaphragm.2 We have encountered a retrocaval sonographic \"mirror artifact\" in a patient with Hodgkin's lymphoma. The physical principles and the specific anatomic structures that cause this finding are explained. Its incidence in sonographic studies of the

Algorithms For Limited-Angle Computed Tomography

Abstract: Limited-angle computed tomography was studied in a project to develop algorithms for a limited-angle scanner. Both the ART algorithm and an orthogonal function algorithm were investigated. The artifact produced by the different methods was very similar. A method is presented for producing model limited-angle artifact in phantom images. Filters are investigated for reducing the artifact, and it is shown that substantial improvement in subjective quality of images can be obtained. This method can be incorporated into limited-angle convolution back-projection algorithms.© (1982) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

[EEG night sleep recording: evaluation with automatic data analysis].

Abstract: Sleep investigations were made in a laboratory using both traditional polygraphic methods and a portable home recording system (Medilog-Recorder 4-24). The evaluation was done by an automatic analysis. For the division into the particular sleep stages (classification of Dement and Kleitman) at least the diversions of 2 EEG and 1 EOG-channel were found to be necessary. As a further parameter the measurement of the pulse frequency was used. After the determination of the frequency-spectrum by the Fast Fourier Transformation a power spectrum was made in order to register the changes of voltages (in periods of 30 seconds) with a sample rate of 128 and a frequency resolution of 0.5 Hz. To evaluate the EOG, a band pass filter was used and after the determination of a level of 15 microV only activities over this value were regarded. Furthermore an automatic artifact detection was fit into the program. The activities of the EEG, the EOG and the pulse frequency were compared with the normal values of the stages and, after that, the particular sleep phases were determined.

Pacemaker recycle from repolarization artifact.

Abstract: Pacemaker \"eccentricity\" can be defined as an unexpected variation from the presumed normal function not caused by pacemaker malfunction. A variety of pacemaker arrhythmias and ECG oddities have always existed.\"? With programmable pulse generators such \"eccentricity\" may exist at one setting and not at others, compounding the problems of reconstruction of the events and decision concerning normal or abnormal function. Lack of knowledge or understanding of the nature of such a pacemaker eccentricity may have unfortunate consequences such as unnecessary pulse generator replacement, as almost occurred in the patient described.