Showing papers on "Artifact (error) published in 1989"

EEG biofeedback method and system for training voluntary control of human EEG activity

Abstract: A biofeedback method and system for use to train a person to develop useful degrees of voluntary control of personal electroencephalogram (EEG) activity. A plurality of EEG potentials from a plurality of locations on the head are individually amplified and filtered in accordance with strict criteria intended for processing in accordance within time constraints limited by natural neurological reactivity. Each resultant signal is processed to provide objective data on brain energies as a function of frequency. Data are presented in real time to the trainee in the form of preselected auditory tones and/or vibro-tactile stimuli indicating with high fidelity the details of EEG activity at a multiplicity of cortical sites. Features of auditory feedback promote learning as well as identification and elimination of spurious artifact states. At periodic intervals, the auditory feedback is supplemented by sensory presentation of digital scores summarizing performances in a metric proportional to brain energy output in the feedback parameters. The scores may be presented as illuminated numerical displays, aurally or both. The system is preferably in an environment designed to control the arousal level of the trainee and the degree of distractibility so as to maximize the learning of voluntary self-control.

Artifact Suppression in Digital Chest Radiographs Enhanced With Adaptive Histogram Equalization

Abstract: Adaptive Histogram Equalization (AHE) has been applied to high resolution digital chest radiographs to provide contrast enhancement. The method provides good contrast in uniform areas of the image, e.g. the lung field, but in so doing both overenhances noise and produces an artifact at boundaries between high density and low density regions. The artifact, which appears as a band of very low contrast data spanning such a boundary, has the effect of suppressing structural information. Although it is known that the problem of overenhancing noise is controlled by the algorithm known as Contrast Limited Adaptive Histogram Equalization (CLAHE), the boundary artifact is not removed by this technique. This paper concentrates on the boundary artifact. We present a method for processing a chest radiograph by means of background subtraction prior to applying the CLAHE algorithm which reduces contrast at high/low density boundaries and thus permits contrast enhancement free of both noise and boundary artifacts.

Reduction of truncation caused artifacts

Abstract: Elimination of truncation artifacts in Magnetic Resonance Images is accomplished by analaytically optimizing controllable parameters; ie, filter characteristic and assymetry ratio when asymetrically sampling arid time domain filtering followed by complex conjugating the filtered data to reduce the Gibbs artifact

Renal duplication artifact in US imaging.

Abstract: To determine the appearance of artifactual renal duplication in ultrasound (US) imaging, the authors analyzed 22 examples of such duplication in 20 patients. The artifact appeared as a duplication of the collecting system in 18, as a suprarenal mass in three, and as upper-pole cortical thickening in one. It occurred in the left kidney in 15 patients, in the right kidney in three, and bilaterally in two. To determine the frequency of the artifact, 50 additional patients were scanned. It was identified in eight of these patients. Imaging characteristics and the results of in vitro modeling proved the artifact was due to sound beam refraction between the lower pole of the spleen or liver and adjacent fat. This artifact is much more common in the left kidney and occurs more frequently in obese patients. Knowledge of the appearance and cause of this artifact should help radiologists avoid diagnostic errors.

The correction of nonuniform signal intensity profiles in magnetic resonance imaging.

Abstract: The increasing use of digital image data in Radiology has opened the door to the routine use of numerical image-enhancement techniques. Of course, numerical image processing cannot put information into the image which is not already there. However, if some means can be found to separate diagnostic image information from noise or artifact, the diagnostic information can be extracted with post-processing. The diagnostic quality of an exam may be enhanced by such numerical manipulations, even though technically, the information content of the digitized image is reduced.

Correlation artifacts in speed of sound estimation in scattering media.

Abstract: A recently described method for speed of sound estimation in tissues in pulse-echo mode involves reception of echoes generated by an ultrasonic pulse by means of a linearly tracking transducer. When the peaks of echo amplitudes are used as markers of arrival time, stairstep-like artifacts appear in the echo arrival time vs. transducer position plots. We postulate that these artifacts area consequence of the speckle phenomenon commonly encountered in ultrasonic imaging. To test this hypothesis, we report computer simulations and water tank experiments which demonstrate similarities between the behavior of the stairsteps and the properties of ultrasonic speckle. Additionally, equations describing the precision of the speed of sound estimation in terms of the second order statistical properties of the stairstep artifact are derived.

Method of deriving a respiration signal and/or a cardiac artifact signal from a physiological signal

Abstract: A method of deriving a respiration signal and/or a cardiac artifact signal is obtained from a physiological signal, in particular an impedance pneumography signal, is disclosed. After detection of the heartbeat moment, the amplitude of the physiological signal at the heartbeat moment is stored. From the difference of the instantaneous amplitude of the physiological signal and the stored amplitude thereof as well as on the basis of a previous learning signal, a learning signal is calculated and stored, which is either read out starting each time with the particular heartbeat moment for deriving the cardiac artifact signal, or which is subtracted from the physiological signal at each heartbeat moment for deriving the respiration signal.

Trigeminal neurilemoma: appearance on magnetic resonance imaging.

Abstract: Neurilemomas can arise anywhere along the trigeminal nerve, and therefore can be either intra-axial or extra-axial. Small neurilemomas in Meckel's cavity may not be detectable with CT scanning because of bone artifact or normal enhancement of the cavernous sinus. We have reported two patients with trigeminal neurilemoma who were evaluated preoperatively with magnetic resonance imaging.

Artifact detection in sleep EEG recording

Abstract: An investigation was conducted with the aim of achieving a completely automatic detection of artifacts resulting from muscular activity and ocular movements superimposed on an electroencephalogram (EEG) signal. Muscular artifacts were detected by a pattern-recognition approach; different features were tested to achieve reliable and real-time results. Pattern classes were constructed based on selected features and using the K-means clustering algorithm. Fisher's linear discriminant, Mahalanobis distance, and the Q-NN rule were the methods tested within the task of supervised classification, using the pattern classes found in the clustering step. Ocular artifacts were detected by an algorithm which compares simultaneously recorded EOG (electrooculogram) and EEG signals. Whenever a significant correlation between them is found, an ocular artifact is detected. If one or both of those artifact types are detected, the actual segment is replaced by an EEG simulation using an AR (autoregressive) modeled system driven by Gaussian white noise at its input. >

A near-optimum filter for suppressing motion artifact in oscillometric signal

Abstract: A near-optimum motion artifact filter which permits oscillometric occlusion pressure determinations to be performed under conditions of moderate surgical limb manipulation is presented. The authors outline the development of the filter and compare its signal-to-noise ratio (SNR) performance to that achieved by patient-specific optimum digital filters. Experiments show that for the oscillometric signals studied, the patient-specific optimum filter can be replaced by a single analog filter with little degradation in motion artifact suppression. >

Speckle reduction in two easy steps

Abstract: A somewhat unorthodox technique for speckle reduction in medical ultrasound pulse-echo images is discussed. Two basic difficulties must be overcome. Recognition of the artifact is based upon an analysis of the instantaneous (temporal) frequency of the individual RF A-line. Correction of the speckle artifact at the local regions indicated by the recognition procedure is performed via techniques derived from the frequency-diversity approach. The hybrid temporal-Fourier processing algorithm has the merit of ultimate applicability on a real-time basis. >

Magnetic resonance needle

Abstract: An implement such as a biopsy needle (10) is formed of an alloy which has at least 35% and preferably about 49% nickel content. When the alloy is used to form a needle the high nickel content of the allow creates an artifact of a size to provide a sufficient needle image for localisation without obscuring the underlying anatomy.

A sampling artifact in the UGC evaluation of research performance

Abstract: The UGC evaluation of research performance in British universities contained a sampling artifact which potentially contributed to an overestimation of the performance of larger departments. The statistical principles underlying the artifact are elucidated, and the magnitude of the effect is investigated.

Dr. Leidy's soap lady: imaging the past.

Abstract: Conventional radiography with a 35-year-old, portable radiographic unit, a Polaroid processing system, and various speed intensity screens was used to survey an adipocere cadaver. Since the specimen could not be moved, positional strategies that might be used for an immobile emergency room trauma victim were employed to assess skeletal components, and organ and artifact locations.

Artifacts in magnetic resonance imaging of the head

Abstract: The results of 505 magnetic resonance (MR) imaging examinations of the head disclosed several different types of artifact. Various artifacts observed with two-dimensional Fourier transformation are described and illustrated. All images were obtained with a 0.5 Tesla superconducting MR imager. About 70% of all images contained artifacts. Phase encoding artifacts due to motion or flow were most frequently observed. Center, "zipper," truncation, radiofrequency, and ferromagnetic artifacts and contrast error on inversion recovery (IR) images were noted less frequently. Phase encoding artifacts and contrast errors on IR images totally degraded the images, and "zipper" artifacts were regional. Center artifacts resembled small infarctions, and ferromagnetic artifacts sometimes mimicked hematomas. It is important to recognize these artifacts and to devise methods to avoid their influence on the region of interest.

"Kirlian photography" film artifacts.

Abstract: A film artifact due to static discharges from the fingers is described. These are similar to Kirlian photographs, ostensibly representing the radiant spiritual aura.