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PubMed1980

Visual discrimination deficits of reading-disabled children: sex artifact?

Several theorists have suggested that deficits in visual discrimination play an etiological role in the development of reading deficits in children who are diagnosed as learning-disabled. Supporting this theory, a number of studies have shown that disabled readers make more errors on visual discrimination tasks than do good readers. The present study, however, suggests that those findings may have been due to a sex-difference artifact. Thirty-six 8- and 9-year-old good readers and reading-disabled children of both sexes responded to 40 matching items under untimed conditions. Males made more errors than females, but overall, reading-disabled children made no more errors than good readers. These findings, along with a reanalysis of previous studies, suggest that because reading disabilities are more common in males, evidence construed as supporting a visual discrimination hypothesis may have been an artifact of a sex difference in studies in which sex was not controlled.

Child↗

PubMed1993

Ocular artifacts in recording EEGs and event-related potentials. II: Source dipoles and source components.

The source dipoles for blinks point radially whereas the source dipoles for saccades point tangentially, in the direction of the eye movement. This indicates that blink potentials are not generated by eye movements but by the eyelid sliding down over the positively charged cornea. Dipole source dipole analysis shows that the "rider artifact" at the onset of upward and lateral saccades is caused by the eyelid as it lags a little behind the eyes at the beginning of the movement. Dipole source analysis allows both the EEG and the EOG to be modeled simultaneously and EOG generators to be distinguished from nearby EEG generators. Ocular source components can be calculated from a principal component analysis of EEG and EOG recordings during blinks and saccades. The effectiveness of propagation factors, source dipoles and source components in removing ocular artifacts from EEG samples was assessed. The most effective correction procedure uses source components.

Adolescent↗

PubMed1989

Imaging artifacts in mechanically driven ultrasound catheters.

Mechanically driven catheter tip echo systems presently operate with a flexible shaft. Rotation power from a proximally mounted motor is transferred via this shaft to the rotating echo tip element. In practice, the tip does not identically 'follow' the rotation of the motor due to low torsional rigidity of the shaft, which creates artifacts in the displayed cross-sectional image. In order to visualize curved arteries such as the coronary arteries, a compromise is necessary between the required low flexural rigidity and a high torsional rigidity. In this report the image artifacts of mechanically driven systems are presented that are related to catheter tip motion. The properties of a spiral drive-shaft and a solid drive-shaft have been compared for rotational speed of 1000 and 3000 revolutions per minute (rpm), and for straight as well as strongly curved catheters. By way of example, the periodic angle error varies from 25 degrees top-top in a straight catheter to 80 degrees top-top when the catheter is curved with R = 20 mm, using a spiral drive-shaft at 1000 rpm.

Angioplasty, Balloon↗

PubMed1985

Algorithm for the correction of artifacts.

The sources of vitreous fluorophotometry artifacts are described. An algorithm to define this "spread function" is presented. The use of improved instrumentation and compensation for this artifact by data processing of the "correction" algorithm can improve the results of vitreous fluorophotometry. This algorithm was carried out in 40 eyes and was found to have an error of 0.7 mg/ml at 3 mm from the choroid-retina.

Choroid↗

PubMedDate not supplied

Evaluation of ferromagnetism and magnetic resonance imaging artifacts of the Strecker tantalum vascular stent.

A woven tantalum vascular stent (Strecker stent) was tested for ferromagnetism at 4.7 T and underwent magnetic resonance imaging (MRI) in vitro and in vivo at 1.5 T to evaluate the production of magnetic susceptibility artifacts. No ferromagnetism was detected. Spin-echo, phase reconstruction, and gradient echo images revealed a low level of susceptibility artifacts both in vitro and in vivo. Our findings demonstrate the feasibility of using MRI to evaluate blood vessels noninvasively following tantalum stent placement.

Animals↗

PubMed1998

Motion artifacts reduction in DWI using navigator echoes: a robust and simple correction scheme.

NMR signal phase variation caused by macroscopic motion of an object during application of the diffusion gradient is a well-known effect in diffusion-weighted imaging (DWI) using the standard pulsed gradient spin-echo sequence (PGSE). This phase error causes severe ghost artifacts in the output image when phase encoding techniques, such as two dimensional Fourier transform (2DFT) imaging, are used. One possible way to eliminate the motion effects is the navigator echo technique. The method is based on estimating the phase error from the navigator echo and using it for the correction of the image echo. The phase errors (zero and first order) for the phase correction of the image echo are usually evaluated from the navigator echo after Fourier transform (FT) in the readout direction, correcting for both translation and rotation. We present here a simple algorithm which enables evaluation and correction in the time domain of phase errors induced by motion. This approach has the advantage of improved correction of motional artifacts and minimized sensitivity to noise and inaccurate setting up of the experiment.

Algorithms↗

PubMed1998

A lung ultrasound sign allowing bedside distinction between pulmonary edema and COPD: the comet-tail artifact.

OBJECTIVE: Acute cardiogenic pulmonary edema and exacerbation of chronic obstructive pulmonary disease (COPD) can have a similar clinical presentation, and X-ray examination does not always solve the problem of differential diagnosis. The potential of lung ultrasound to distinguish these two disorders was assessed. DESIGN: Prospective clinical study. SETTING: The medical ICU of a university-affiliated teaching hospital. PATIENTS: We investigated 66 consecutive dyspneic patients: 40 with pulmonary edema and 26 with COPD. In addition, 80 patients without clinical and radiologic respiratory disorders were studied. MEASUREMENTS: The sign studied was the comet-tail artifact arising from the lung wall interface, multiple and bilaterally disseminated to the anterolateral chest wall. RESULTS: The feasibility was 100%. The length of the examination was always under 1 min. The described pattern was present in all 40 patients with pulmonary edema. It was absent in 24 of 26 cases of COPD as well as in 79 of 80 patients without respiratory disorders. The sign studied had a sensitivity of 100% and a specificity of 92% in the diagnosis of pulmonary edema when compared with COPD. CONCLUSIONS: With a described pattern present in 100% of the cases of pulmonary edema and absent in 92% of the cases of COPD and in 98.75% of the normal lungs, ultrasound detection of the comet-tail artifact arising from the lung-wall interface may help distinguish pulmonary edema from COPD.

Adolescent↗

PubMed2002

Effect of subcutaneous butylscopolamine administration in the reduction of peristaltic artifacts in 1.5-T MR fast abdominal examinations.

In abdominal MR imaging, ghost artifacts from noncyclic bowel movements can reduce the quality of the images. Although pharmacologic suppression of motion is effective, no study has being conducted to analyze the influence of drug motion suppression on fast breath-hold 1.5-T examinations of the upper abdomen. A prospective, randomized, double-blind trial was conducted in 50 patients. Patients were randomly distributed into two groups: The control group received only an oral solution, whereas the other group received the oral solution plus a subcutaneous injection of 20 mg of butylscopolamine 10 min before the MR examination. Breath-hold T1-weighted gradient-recalled-echo (GRE) MR images were obtained in a 1.5-T superconductive unit. Quantitative image analysis was performed with region-of-interest (ROI) measurements of the signal intensity of the liver and in background air anterior and lateral to the patient. A qualitative analysis of the subjective quality of the T1-weighted images was also done, and the adverse reactions were registered. The groups were homogeneous regarding age, gender, and weight distribution. No significant differences in the signal intensity of the liver and in the incoherent noise measurements were found between the two groups. Gastrointestinal noise showed significant differences between groups, with lower values for the butylscopolamine group compared with the control group. There was also a statistically significant difference in the image quality between groups, and optimal studies were only found in the butylscopolamine group, where most patients had a good-quality evaluation. Regarding adverse events, there were non-significant differences between groups. In conclusion, administration of an antiperistaltic agent to reduce the movements of the gastrointestinal tract diminishes the motion artifacts generated on MR imaging of the abdomen, even at high field strength and with fast imaging sequences. Images of the upper abdomen obtained after pharmacologic suppression of the gastrointestinal movement are of significantly superior quality.

Abdomen↗

PubMed1984

Avoidance of artifacts on computerized tomograms by selection of appropriate surgical clips.

Surgical clips (metallic or plastic) are frequently used for hemostasis and tumor marking. This study evaluated the radiographic and computerized tomographic appearance of different clips and their relative interference with computerized tomographic scans. Metallic clips (stainless steel, tantalum, and titanium) can all be seen on plain radiographs. Tantalum clips caused extensive distortion on computerized tomographic scans which would interfere with scan interpretation. Both stainless steel and titanium clips resulted in much less artifact and interference on computerized tomographic scans. Recent studies have suggested that there may be some risk of torsion of stainless steel clips in nuclear magnetic resonance scanners resulting in tissue damage. Absorbable plastic clips cannot be seen on plain film but are visualized on computerized tomographic scans and do not appear to cause scan artifact. Overall, we recommend the use of either titanium hemostatic clips when tumor marking on plain film is required or plastic clips when tumor marking is less important.

Evaluation Studies as Topic↗

PubMed1984

Artifacts associated with 2-mercaptoethanol upon high resolution two-dimensional electrophoresis.

The presence of 2-mercaptoethanol in the protein denaturing solution used to prepare samples for high resolution two-dimensional electrophoresis can result in artifacts when the two-dimensional patterns are detected by silver staining. These are (i) spots of discrete isoelectric point and electrophoretic mobility, (ii) horizontal bands of the same electrophoretic mobility as the spots (corresponding predominantly to molecular weights of 54,000 and 68,000), and (iii) vertical streaks of variable length and intensity. Although the nature and source of artifacts have not been positively identified the evidence suggests that they are probably not inherent in the 2-mercaptoethanol itself but rather released by the latter from some component common to both the first- and second-dimension constituents of the electrophoretic system.

Electrophoresis, Polyacrylamide Gel↗

PubMed1986

Detection of dextransucrase and levansucrase on polyacrylamide gels by the periodic acid-Schiff stain: staining artifacts and their prevention.

One use of the periodic acid-Schiff (PAS) stain is to detect dextransucrase and levansucrase activities on polyacrylamide gels by staining their polysaccharide products, dextran and levan. When gels with heavy dextran or levan bands were PAS stained, proteins other than dextransucrase and levansucrase also were stained, and a high background developed during storage. The staining of proteins other than dextransucrase and levansucrase is caused by the diffusion of the periodate-oxidized carbohydrate before and after staining. This diffusion could be greatly slowed, and the staining artifact decreased, by following the PAS stain by a crosslinking treatment of the carbohydrate-dye complex. Protein staining artifacts could be prevented by using chymotrypsin to remove the protein from the gel at the stage after polysaccharide synthesis but before the PAS stain.

Chymotrypsin↗

PubMed1989

Artifacts following gold staining of Western-blotted membranes.

Protein samples were separated by sodium dodecyl-sulfate-polyacrylamide gel electrophoresis, electrophoretically transferred to nitrocellulose membranes, and stained with colloidal gold. Three artifact bands appeared demonstrating apparent molecular weights of 58,000, 63,000, and 65,000. The appearance of these bands was due to oxidized dithiothreitol used to denature the proteins prior to electrophoresis. The appearance of the artifact bands could be avoided by the addition of excess iodoacetamide to the denatured protein sample and by limiting staining time to 1.5 h at 13 V/cm.

Blotting, Western↗

PubMed1990

Binding of substrates to cytochrome P450 enzymes: mathematical artifacts in the application of difference spectrophotometry.

Investigation of the difference absorption spectrum has been a common method for studying many aspects of hemoproteins such as cytochrome P450. The difference spectrophotometric technique, as applied in studies on binding of substrates to cytochrome P450, has resulted in certain mathematical artifacts which have been mistaken for real changes in binding equilibria. The purpose of this paper is to point out these artifacts.

Binding Sites↗

PubMed1978

Identification of a potential artifact in the use of electron microscope autoradiography to localize saturated phospholipids in cells.

The suitability of electron microscope autoradiography for sutdying the uptake and intracellular localization of lipid vesicles (liposomes) containing radiolabeled saturated phospholipids has been examined. Data are presented showing that preparation of specimens for electron microscope autoradiography by conventional methods is accompanied by significant translocation and intercellular redistribution of radiolabeled saturated lipids, causing spurious labeling patterns. Intercellular redistribution of radiolabeled lipid was demonstrated by mixing glutaraldehyde-fixed mous L1210 cells that had been incubated with sonicated lipid vesicles containing [H] dipalmitoyl phosphatidylcholine with an indicator cell population (fixed avian erythrocytes) which had not been exposed to vesicles and showing that after electron microscope processing radiolabeled grains were present in both cell types. The same redistribution artifact also probably affects the intracellular localization of radiolabeled lipids. This artifact is discussed in relation to previous work in which autoradiographic methods have been used for ultrastructural localization saturated phospholipids in cells and tissues.

Animals↗

PubMed1978

A spectral method for removing eye movement artifacts from the EEG.

A frequency-domain technique for compensating for eye artifacts in mid-line scalp EEG when power spectra are to be calculated is reported. It has been tested in 12 subjects during voluntary and random eye movements. The method which involves calculating the ratio of EEG and EOG spectra adequately controls for low-frequency components in the EEG due to eye artifacts and allows recovery of the dominant peaks in the scalp EEG spectrum.

Electroencephalography↗

PubMed1979

Automated detection of EEG artifacts during sleep: preprocessing for all-night spectral analysis.

This paper describes a simple artifact detection algorithm which can be used when large amounts of EEG data are to be automatically processed via spectral analysis techniques in a general purpose digital computer, and visual inspection of each EEG epoch becomes an impossible task. The technique is based on a chi-square (chi(2)) goodness-of-fit test to a Gaussian distribution (CSQ), and it was applied to EEG epochs each 30 sec long. This test proved to be very sensitive to non-stationarities in the EEG amplitude distribution for a particular epoch, and it produced a large value for the chi(2) coefficient when an artifact was present. EEG epochs that gave rise to chi(2) coefficients of value larger than a heuristically determined minimum were discarded from further analysis. The above technique enabled efficient data reduction and reliable automatic off-line processing of 50 nights of sleep EEG via spectral techniques.

Action Potentials↗

PubMed1980

Respiration-linked 'limbic spindles': vibration artifact recorded from nasopharyngeal and intracerebral electrodes.

Respiration-linked 20-40 c/sec spindles were recorded simultaneously from nasopharyngeal, sphenoidal and limbic depth electrodes in 10 patients under evaluation for temporal lobectomy. In addition, a piezo-electrode at the tip of one nasopharyngeal electrode recorded vibration from the nasopharynx in 3 patients. Results demonstrated that respiration-linked 20-40 c/sec spindles recorded from nasopharyngeal and sphenoidal electrodes are vibration artifact. In addition, similar vibration artifact also occurred in the limbic depth, indicating that at least some respiration-linked intracerebrally recorded limbic spindles also are not of neuronal origin.

Electroencephalography↗

PubMed1987

Surgical suction damage: a common tissue artifact.

The vacuum effect of a surgical suction tip can induce significant artifactual alterations in the connective tissue of specimens removed for diagnostic or therapeutic purposes. The alterations described in this article consist of a surgical suction artifact characterized by the formation of numerous, pleomorphic vacuoles that, on casual microscopic examination, resemble the morphology of traumatized adipose tissue. This artifact occurs when a vacuum draws air into connective tissue and mobilizes connective tissue mucins (acid mucopolysaccharides) that localize within the vacuoles that are formed.

Connective Tissue↗