Showing papers on "Artifact (error) published in 1990"

Method of and apparatus for multi-vector pacing artifact detection

Abstract: A technique for improving detection of the pacing artifact in patients having artificially paced myocardial contractions. The improved detection is accomplished by sensing all three commonly monitored EKG leads. Each lead is differentially amplified and rectified to produce a signal of absolute value. The resulting three signals are algebraically summed and differentiated. Because the pacing artifact consists of higher frequency components than the naturally occurring QRS complex, it can easily be detected by its much larger first derivative. Reliable detection of the artificial pacing artifact is extremely important in monitoring and programming implantable pacers. It is necessary to accurately determine whether a pacing pulse has been delivered and precisely measure the time of its occurrence.

Design and testing of artifact-suppressed adaptive histogram equalization: a contrast-enhancement technique for display of digital chest radiographs.

Abstract: One of the goals of our research in the field of digital radiography has been to develop contrast-enhancement algorithms for eventual use in the display of chest images on video devices with the aim of preserving the diagnostic information presently available with film, some of which would normally

Multichannel adaptive enhancement of the electrogastrogram

Abstract: The electrogastric signal can be measured cutaneously on the abdomen. This is harmless to patients and volunteers. However, the poor quality of the cutaneous measurements necessitates signal enhancements. Hence, an adaptive multichannel signal enhancing system is proposed. The mu -vector least-mean-square algorithm is applied to adjust the weights of the adaptive filters in the system. A detailed description and a performance analysis of the system is given. The proposed system allows the respiratory artifact, the electrode-skin noise, some motion artifacts, and the electrocardiography to be efficiently reduced whole the characteristics of the relevant signal are less affected. >

Color Doppler artifact in anechoic regions.

Abstract: For color Doppler imaging, several types of signal processing are employed in order to produce acceptable images of blood flow in blood vessels while suppressing color in moving solid tissue. The processing can produce an artifact in which color may arise from noise or from tissue motion and fill anechoic regions preferentially. This artifact may complicate the differentiation of areas with blood flow from anechoic regions without flow. By using four different color Doppler ultrasound units to image a tissue-equivalent phantom containing anechoic cylinders, artifactual color resulted when gain was raised sufficiently. This color was concentrated in anechoic regions of a gray-scale image that did not contain flow. In two instruments, this artifact was only observed when the transducer was vibrated, simulating tissue motion. In these instruments, the identification of low-frequency, high-amplitude Doppler signals is used to locate moving solid tissue and so suppress color in these regions. In the other two instruments, the presence of echoes within the image suppressed the assignment of color. With both types of processing, color may appear artifactually in echo-free regions without flow, such as fluid collections. Presence or absence of flow should be confirmed by Doppler spectral analysis. An understanding of the origin and appearance of artifactual color can prevent its occurrence from detracting from the usefulness of color Doppler imaging.

Artifact Size and Lateral Displacement under Tillage: Comments on the Odell and Cowan Experiment

Abstract: Odell and Cowan's (1987) experimental study largely confirms and extends results obtained by Lewarch and O'Brien (1981) on the effects of tillage on artifact distributions in the plow zone. In contrast to earlier studies, however, theyfind no relation between artifact size and lateral-displacement distance. The lack of relation between these two variables may be a consequence of defects in experimental design and analysis and should be considered suspect until better controlled data are available.

Motion Artifact In Pulse Oximetry

Abstract: Data suggests that the source of “motion artifact” with transmission pulse oximetry is blood volume changes in the extremity being measured rather than changes in relative motion between the sensor and the subject during subject activity. Comparison between a finger clamp sensor, disposable taped on sensor and individual sensor elements glued on the fingertip showed no statistically significant difference in motion artifact. Standard movements of the hand and arm did, however, show differences in artifact when the movement was vertical compared to the same movement in the horizontal plane. compared for different maneuvers and different sensors using the Student’s t-test and analysis of variance.

The ALOPEX Process: Application To Real-time Reduction Of Motion Artifact

Abstract: A neural network algorithm is presented which provides real-time reduction of motion artifact from blood pressure pulse signals. When provided with one pulse signal and a multiplicity of noise inputs, the algorithm seeks the global minimum of the error surface, by adjusting a single weight for each noise input. The global minimum represents the best combination of common mode gain adjustment, ensemble averaging, and noise rejection. The algorithm is based both on the ALOPEX process, and a parallel adaptive technique devised for real-time cancellation of common mode artifact from the blood pressure pulse.

Use Of Evolutionary Programming In The Design Of Neural Networks For Artifact Detection

Abstract: This paper applies evolutionary programming to the design of neural networks for artifact detection in pulsatile arterial pressure waveforms. Evolutionary programming is an efficient search scheme which avpids the tendency of back propagation to get detained in local minima. Use of this technique reduced the complexity of a neural artifact detector[3] from 21 hidden nodes to two with very little penalty in classification error.

Is pseudomonilethrix an artifact

Abstract: The scanning electron microscope (SEM) has proved to be a very useful tool in the study of morphologic hair shaft abnormalities, in particular because of its depth of field and resolution compared with other optical instruments.' The observation of a regular fusiform nodular formation is characteristic of monilethrix. This hair dysplasia presents fusiform nodes alternating with amedular narrow zones with a smaller diameter than normal hair. Those narrow sites are the points at which the hair fractures. Currently it is known that this alteration starts in the follicular keratinization area with structural changes of the cortex and cuticula. Longitudinal grooves are often present on the internodes. The inheritance of monilethrix is usually autosomal and dominant and this abnormality appears in early childhood, mostly in the occipital area and neck nape. Keratotic follicular plugs with short brittle and beaded hairs in the affected areas are also characteristic. Eractures appear easily at a few millimeters from the skin surface, and alopecia can be severe. In monjiethrix the cross section of the hair shaft remains almost circular at any level, Pseudomonilethrix has been described by Bentley-Phillips et al.-̂ -̂ in four families of Dutch, German, British, and Indian origin as an autosomal condition. This abnormality bears a resemblance to classical monilethrix, but it is morFic. 1. Images of pseudomonilethrix induced in normal hair by applying a moderate pressure of crossed bairs between two glass slides.

Nuclear magnetic resonance multi-echo imaging method and apparatus

Abstract: A nuclear magnetic resonance multi-echo imaging method and an apparatus therefor in which gradient field pulses having predetermined products of intensity and time are applied on both sides of an inversion pulse in at least two of three directions which are orthogonal to each other to dephase components of a magnetization vector which leads to an artifact signal and an error signal, whereby only a normal echo signal can be sampled to form a correct image.

Method for detecting artifact signal components

Abstract: A method for detecting artifact signal components comprises the steps of detecting an image signal made up of a series of image signal components representing a radiation image from a recording medium on which the radiation image has been recorded. Specific image signal components, which have values smaller than a predetermined threshold value, are detected from the image signal. Investigation is made to find how many neighboring picture elements the specific image signal components correspond to. In cases where the number of the neighboring picture elements is smaller than a predetermined number, it is determined that the specific image signal components are artifact signal components.

Potential misinterpretation of cervical spondylosis with cord compression caused by metallic artifacts in magnetic resonance imaging of the postoperative spine.

Abstract: Tiny metallic particles produced by the contact of untempered surgical instruments with a diamond drill produce magnetic susceptibility artifacts that can both limit the diagnostic quality of postoperative magnetic resonance imaging of the cervical spine and cause diagnostic error. A case of cervical pseudospondylosis with apparent cord compression due to such an artifact is presented. The source of these metallic particles is considered, and the nature of the susceptibility artifact is discussed.

An algorithm for the suppression of translational motion artifacts in MRI.

Abstract: The quality of Magnetic Resonance imaging systems has improved to the point that the motion is the most important limitation in many examinations. Gross movements of the patient cause a ghost artifact in the image which can interfere with the diagnosis. In this paper a new method is presented to suppress the translational motion artifact caused by gross movements. The method uses postprocessing on a standard two-dimensional Fourier transform image. It is shown that translational motion causes an additional phase factor in the detected signal and that this phase error can be removed using an iterative algorithm of generalised projections. The method has been tested using computer simulations and successfully removed most of the artifact, even in the presence of noise.

Ghost artifact on gradient-echo imaging: a potential pitfall in hepatic imaging.

Abstract: Standard evaluation of the liver with MR uses spin-echo imaging with Tiand T2-weighted pulse sequences [1]. A short inversion-time inversion recovery (STIR) sequence has been used as an adjunct to standard pulse sequences because it provides certain advantages, including fat suppression, additive effects of Ti and T2 relaxation on tissue brightening, and a high signal-difference-to-noise ratio in the detection of liver metastases [2, 3]. All of these sequences require a long acquisition time and thus are compromised by motion and respiratory artifacts. The recent use of gradient-echo imaging to scan the liver allows acquisition of data within a single breath-hold [4]. In using this technique to examine patients with various types of hepatic disease, we noticed a disturbing artifact that mimicked a space-occupying lesion. Appreciation of this artifact is important in interpreting scans acquired with a gradient-echo pulse sequence.

Automated Identification Of Artifact-free Diastolic Heart Sounds

Abstract: Detection of sounds associated with turbulent blood flow in partial occluded arteries is the basic assumption underlying an ongoing project to noninvasively diagnose coronary artery disease To improve detection, background noise in recorded heart sounds is minimized by isolating the diastolic segment through the use of a carefully placed “analysis time window“ Additionally, heart sound recordings containing excessive artifact are eliminated through a data editing procedure Previously, data editing and windowing was accomplished in a manual procedure utilizing an interactive graphics display An automated procedure for window placement and data editing is described which performs at least as well as manual methods I” A reliable and inexpensive procedure for

Digital processing of equine exercise electrocardiograms.

Abstract: We have developed and used a system for recording and analyzing the electrocardiogram (ECG) of the horse during exercise. The system consists of a commercial ECG transmitter telemetering a Z lead (base-apex) ECG from an exercising horse. The received data are then remodulated at an audio frequency and stored on a audio cassette recorder. Exercise protocols of up to 10 minutes are digitized using a Macintosh II computer. For rhythm analysis, a computer program to identify the various waves of the ECG uses a modification and refinement of the integrated-squared-derivative (ISD) technique. This technique consists of frequency selective digital filtering and differentiation followed by integration of the squared derivative. The waves of the ECG are identified using adaptive thresholding of the ISD and the derivative of the ECG. Thus far, we have been able to successfully identify the Q, R, and the end of T in ECGs severely contaminated by exercise artifact. The system can place the absolute time of occurrence of the Q, R, and end of T in a text file for export to other analysis programs such as spreadsheets and statistics packages.

Geometric effects in tomographic reconstruction

Abstract: In x-ray and ion-beam computerized tomography, there are a number of reconstruction effects, manifested as artifacts, that can be attributed to the geometry of the experimental setup and of the object being scanned. In this work, we will examine four geometric effects that are common to first-and third-generation (parallel beam, 180 degree) computerized tomography (CT) scanners and suggest solutions for each problem. The geometric effects focused on in this paper are: X-pattern'' artifacts (believed to be caused by several errors), edge-generated ringing artifacts (due to improper choice of the reconstruction filter and cutoff frequency), circular-ring artifacts (caused by employing uncalibrated detectors), and tuning-fork artifacts (generated by an incorrectly specified center-of-rotation). Examples of four effects are presented. The X-pattern and edge-generated ringing artifacts are presented with actual experimental data introducing the artifact. given the source of the artifact, we present simulated data designed to replicate the artifact. Finally, we suggest ways to reduce or completely remove these artifacts. The circular-ring and tuning-fork artifacts are introduced with actual experimental data as well, while digital signal processing solutions are employed to remove the artifacts from the data. 15 refs., 12 figs.

Reducing EMG Artifact In EEG Recording With Standard Median Filter And FIR-median Hybrid Filter

Abstract: When we detect spikes and seizures in EEG recording from epileptic patients with scalp electrodes, the recordings often are partially or totally obscured by EMG artifact from scalp muscles. This makes the visual interpretation extremely difficult. Gotman and Lawrence used the linear digital filter to reduce the EMG artifact in EEG recording. In this paper, the nonlinear filtering techniques, Standard Median filter and FIR-Median Hybrid filter are used to reduce the EMG artifact in EEG recordings. This type of filter reduces EMG artifacts without affecting sharp edges of cerebral activity. It does not introduce false rhythmic activity and executes much faster than digital filter.

Echo and artifact: the similarities and differences between print codes and oral codes and their implications for the teaching of composition

Abstract: How we, as Compeigition insttiudtors, and students of writing, view the relationship between oral and written language and the effect of thut Relationship oh the acquisition, productioh, and proGessihg of language will affect the approach we take to writinq and the teaching of writing. It is, theiefOrd, important that we explore how speech and writing influence one another in order to derive a theoretical framework that is apt to guide our practice in a positive way. Chapters One and Two of this thesis examine the characteristics of speech and writing in an attempt to understand how they are acquired, produced, and processed. Chapter Three explores language transfer theory and two main theoretical perspectives on the effect that speech has on the acquisition of writing skills, Finally, Chapter four discusses some of the pedagogical implications of the theory that holds that though speech and writing are related in some important ways, they are essentially two unique sets of