Showing papers on "Artifact (error) published in 1984"

Reducing Motion Artifacts and Interference in Biopotential Recording

Abstract: The application of engineering principles and techniques to biopotential recording has resulted in a continual improvement both in the type and the quality of recorded signals. Physical placement of electrodes has enabled improved discrimination of the biopotential of interest (such as the ECG) from unwanted biopotentials (such as the EMG). Understanding that the major motion artifact in ECG recording arises from the skin and not the electrode has resulted in techniques that reduce this artifact, such as skin abrasion and mechanical stabilization. However, skin abrasion makes the skin more subject to irritation, so mild gels are required. The development of the floating silver/silver chloride electrode has eliminated motion artifact and noise caused by the electrode. The development of the driven-right-leg circuit has greatly reduced interference due to power lines. Adaptive filters have reduced the difficult-to-eliminate interference due to spark-gap electrosurgical units.

Fractionated electrical activity and continuous electrical activity: fact or artifact?

Abstract: ENDOCAVITARY MAPPING during chronic ventricular tachycardia in patients with healed myocardial infarction and/or ventricular aneurysms has been used to locate the region from which ventricular tachycardia originates. During the process of mapping, bipolar electrograms with unusual configurations have been recorded from the chronically ischemic or healed infarcted regions, both with electrode catheters and with hand-held probes. Electrograms consisting of multiple \"high-frequency\" components with low amplitudes (< 1 mV) and long durations that may exceed 100 msec have been termed \"fractionated.\" Although fractionated electrograms have these qualitative descriptors, quantitative criteria to distinguish among various types of electrograms have not been established. Such quantification, however, is limited by the fact that electrogram amplitude and width can vary depending on the interelectrode distance, contact, and degree to which the signal is amplified. We have recently undertaken studies in normal subjects and in patients with infarction and ventricular tachycardia to develop such criteria using a 1 cm interelectrode distance and a fixed gain of I mV = 1 cm. With these methods normal electrograms had amplitudes greater than 3 mV, durations of 70 msec or less, and amplitude/duration ratios of 0.046 or more. Electrograms outside these values were termed \"abnormal.\" Multicomponent electrograms that fell beyond 1 SD from mean values of abnormal electrograms (amplitude 1.4 ± 0.9 mV, duration 93 + 40 msec, ratio 0.017 + 0.012) were termed \"fractionated.\" Although the pathophysiologic significance of the relationship between multicomponent \"abnor-

How to Detect Travel Market Segments: A Clustering Approach

Abstract: A cluster-analytic approach to benefit segmentation is described using an illustrative empirical example drawn from the Austrian domestic travel market. The results demonstrate that some benefits are incompatible with each other at the segment level, and that the "average" vacationer may be only a statistical artifact.

Chemical shift misregistration effect in magnetic resonance imaging.

Abstract: A low intensity artifact appearing at the junction of perirenal fat and renal parenchyma on MR images was recently described. A symmetrical high intensity artifact is also observable on the opposite side of the kidneys as well as at the junction of the right lobe of the liver and adjacent adipose tissue. Both artifacts can be explained as exhibitions of pixel misregistration due to the difference in chemical shifts of fatty and non-fatty organs. Identification of the chemical shift misregistration effect is important since the existence of this artifact may cause erroneous diagnosis of calcification and/or fluid collections.

Multiple measurement noise reducing system using artifact edge identification and selective signal processing

Abstract: Disclosed is a multiple measurement multiple energy x-ray imaging system in which a plurality of measurements are processed to provide a first image signal representing a desired parameter of an object and in which the plurality of measurements are processed to provide a second processed image signal having greater signal-to-noise ratio than the first processed image signal but in which extraneous arti­ facts may be introduced into the signal. The spatial location of the edges of the extraneous artifacts are determined. The first processed image signal and the second processed image signal are combined to provide an improved image signal except at the spatial locations of the extraneous artifacts where the first processed image signal is used for the image signal thereby eliminating the extraneous artifact from the displayed image.

The ghost artifact.

Abstract: A ghost artifact is produced when refraction of an ultrasound beam occurs in one part of a scanning plane. Image duplication or even triplication may result. This may lead to error of diagnosis and measurement. Ghost artifacts are commonly seen in transverse echograms of pelvic organs because the rectus muscle interposed between the transducer and the area of interest is acting as a lens and refracts the ultrasound beam. Three illustrative case reports are presented.

Nuclear magnetic resonance signal artifact removal

Abstract: In an NMR imaging system, two-pulse excitation sequences are used to acquire lines of NMR signal information. Artifact signal components may also be present during the times of NMR signal acquisition. In order to remove these artifacts from the center of the image, the artifact signals are alternately phase-encoded from line to line by alternating the phase of one of said excitation pulses from line to line. Fourier transformation is performed on the lines of information in at least the direction of alternate phasing of the artifact components, which relocates the artifacts to the edge of the resulting image.

Asymptotic Site-Index Curves, Fact or Artifact?

Abstract: In the absence of permanent sample plot data, site-index curves and equations showing the height/age relationship for a tree species growing on a given site have been derived using stem analysis an...

Method for removing the effects of baseline error components in NMR imaging applications

Abstract: A preferred embodiment of a method of removing the effects of nuclear magnetic resonance (NMR) signal baseline error artifacts in imaging applications is disclosed with reference to Fourier transform imaging techniques, of the type frequently referred to as spin warp In accordance with the method, the phase of the radio frequency (RF) excitation pulse is alternated in adjacent phase-encoding views by 180° Since the baseline error component is independent of this phase change, the effect of phase reversal of the RF excitation is to modulate the desired image up to the Nyquist frequency in the phase-encoding direction The artifact due to the baseline error component, however, is unchanged Views measured with -90° RF excitation are negated prior to reconstruction so that the image is returned to its correct position, while the baseline error artifact is modulated to the edge of the field of view Since the baseline artifact has limited bandwidth, it does not interfere with the desired image Because only one measurement is made at each phase-encoding gradient amplitude, the minimum scan time can be halved, the field of view can be doubled, or the resolution in the phase-encoding direction can be doubled

Rx for ECG monitoring artifact.

Abstract: The object of electrocardiographic (ECG) monitoring is the observation and assessment of the heart's electrical activity. Cardiac monitoring has become extremely commonplace in recent years in critical care and ambulatory settings. Electronic advancements have produced instrumentation with the potential of providing accurate information and reliable heart rate alarms. Computerized monitors enhance patient assessment by allowing uninterrupted electronic observation of heart rate and ectopic activity with comprehensive automatic reporting mechanisms. Despite these improvements in instrumentation, monitoring systems continue to be plagued by problems related to poor signals. Wandering baselines, small complexes, fuzzy tracings, and frequent electrode replacement make patient assessment difficult and induce false heart rate alarms. Improvement in electrode preparation techniques and a better understanding of the sources of artifact can enhance equipment performance, resulting in improved patient assessment, more effective utilization of nursing time, and reduced operating costs. This article discusses the physiologic and non-physiologic sources of ECG monitoring artifact and presents a method of electrode site preparation to reduce artifact.

The Rare Male Mating Advantage: An Artifact Caused by Marking Procedures?

Abstract: Many reports on rare male mating advantage have been published (reviews by Petit and Ehrman 1969; Ayala and Campbell 1974; Ehrman and Probber 1978; Ehrman and Parsons 1981; Spiess 1982). A rare male mating advantage can be defined as frequency-dependent male sexual fitness, with the rare type of male having the highest male sexual fitness. Quite often the mating advantage holds for both of two male types when rare. In that case the rare male mating advantage is said to be two-sided; when it holds only for one type when rare it is called onesided. It is not self-evident hat females must choose their mates in a frequencydependent manner for rare male mating advantage to occur. Even when an individual female does not change her receptivity in favor of the rare males, rare male mating advantage can be produced when females differ in their level of preference for a given type of male (O'Donald 1980). More recently Spiess (1982) discussed a model in which rare male mating advantage is produced by female avoidance of the cue of the male first o court, but it also has been suggested that the rare male mating advantage could be an artifact of experimental design (Markow 1980; Bryant et al. 1980; Kence 1981). Markow (1980) found differences in male mating success in Drosophila melanogaster depending on the place in the vial where the males were collected. This can cause a rare male mating advantage if the males are not sampled randomly with respect to place. Bryant et al. (1980) suggested that in many cases the rare male mating advantage is merely an artifact resulting from alternately marking the rare and common strains. Their results are based on a model of mating behavior proposed by Kence and Bryant (1978). Kence (1981) proposed further that, for the case in which marking is alternated and there is some effect of marking on mating behavior, a rare male mating advantage is the natural outcome, even without the application of a special model of mating behavior. Here I question some of the arguments applied in Kence (1981) and Bryant et al. (1980) and discuss the consequences for understanding the causes of rare male mating advantage. First I will show that the simple reasoning of Kence (1981) to account for the rare male mating advantage cannot be applied to the types of experiments that have usually been carried out. Second, evidence will be presented that marking Drosophila will have much less effect than suggested by Bryant et al. (1980). The marking procedure can introduce many problems. Whenever marking is necessary, it should be considered a standard procedure to alternate marking over the replicates to prevent bias. Kence (1981) suggested that even with this precaution there may still be some bias left. It is assumed that there is some effect of marking not shown in a preliminary test, e.g., because the test was applied to too

Exposure artifacts in raster scanned equalization radiography.

Abstract: The image artifacts characteristic of a scanning chest radiographic system are reviewed. The technique employs a pulsed beam of radiation swept in an overlapping raster pattern that can result in severe ripple and scan line artifacts with improper scanning parameters. A one-dimensional treatment of the scanner geometry shows that the artifacts can be eliminated when the beam width is an integral multiple of interpulse spacing. An extension to a two-dimensional analysis indicates that with the collimator geometries employed, artifact-free images are not possible with a fixed x-ray frequency but can be achieved when a variable frequency source is used. A treatment of the sensitivity for artifact formation shows that with proper choice of scanning parameters sizable errors in beam width can be tolerated without significant artifact formation.

Position locating apparatus and method

Abstract: A technique for plotting the provenience of an archaeological artifact with respect to a fixed reference point is disclosed herein. This technique utilizes an apparatus including a base assembly positionable at the fixed reference point, means movable to the location of the artifact from a given starting point, and means connected with the base assembly and the movable means and responsive to movement of the latter to the artifact location from its given starting point for indicating the position of the artifact location within a particular coordinate system, specifically a spherical coordinate system including coordinates phi , theta and rho .

X-ray tv signal processor

Abstract: PURPOSE:To obtain a subtraction image having a high diagnostic ability, with less motion artifact, by detecting the time point of the movement of a personnel to be inspected at an electronic circuit automatically if the personnel is moved after the injection of a contrast medium and replacing the image into a new mask image. CONSTITUTION:If the motion artifact exists, the signals A, B of the motion artifact are outputted in addition to the contrast medium C. The signals A, B are the pictures having a different code and an equal amount theoretically. Since the signal B shows the same density trend as the contrast medium, it is not discriminated from the signal shown by the contrast medium, but the signal A shows the opposite density trend as the contrast medium to discriminate the picture to be the motion artifact. The region of the signal A is measured to know the point of a time when the personnel to be inspected moves and to mask. The region to which the contrast medium flows is limited and its address is preset to a preset 28. The same address of the mask image memory 14 and the live image memory 16 is inputted to an address comparison circuit 26. Further, a switch 13 is switched to the live image memory 16 after the data write. Further, 50 is a circuit detecting the fluctuation of each picture before and after timewise movement and detecting the end of the movement of the motion artifact.

An Injection-Technique Artifact

Abstract: We describe a new artifact relating to improper injection technique: increased localization of radionuclide in an extremity undergoing injection, caused by compression of the extremity in attempts to restrain an individual. The artifact was later simulated by maintaining a tourniquet in place during injection. This is a technical artifact, which is easily preventable. Awareness of the artifact and its cause will prevent false interpretation of such an abnormal localization.

Motion Artifact In 2DFT MR Imaging

Abstract: Respiratory motion has been observed to produce artifacts in MR images of the abdomen and thorax. In order to experimentally characterize this artifact, a phantom was moved cyclically in the imaging field in order to investigate the effects of 1. amplitude of motion, 2. speed of motion, and 3. direction of motion. All images were obtained with a 0.30 Tesla magnet using a spin-echo sequence and two-dimensional Fourier transform, 2DFT, reconstruction. In 2DFT imaging a steady frequency encoding gradient is applied during MR signal acquisition which is preceded by a sequence of varying phase encoding gradients which are perpendicular to the frequency encoding direction. The artifact due to periodic motion consists of repeated copies of the edge of the object which are displaced from the original object in the phase-encoded direction. The distance between the actual object and the first echo is inversely proportional to the number of MR signal acquisitions per motion cycle. The clarity of both the artifact and the object is reduced as the amplitude of motion is increased. Simulations of motion patterns confirm experimental results. Respiratory gating has been applied in both abdominal and cardiac studies. These studies resulted in improved image clarity and elimination of repeated copies of organ edges in the reconstructed image.

Paracardiac pseudotumor: a kymographic artifact of computed radiography

Abstract: The computed chest radiograph (ScoutView, G.E.) has gained widespread acceptance as a means of precisely locating the desired CT scan levels. We describe how apparent lobulation of the cardiac border on that view relates to the kymographic effect of cardiac pulsations during the patient’s passage through the gantry. Failure to appreciate this artifact could lead to the erroneous conclusion that abnormal mediastinal masses are present, especially in cases of known or suspected mediastinal disease.