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At least 1,099 records · Page 61Linked to original sources
PubMed1997

Aneurysm clips made of titanium: magnetic characteristics and artifacts in MR.

PURPOSE: To evaluate the magnetic characteristics, artifact formation, and implant safety of titanium aneurysm clips for use in MR imaging. METHODS: Aneurysm clips made of titanium alloy TiAl6V4 were tested in a magnetometer to determine their magnetic susceptibility and in a 1.5-T MR imager using both a geometric phantom and an animal model. A commercially available alpha-Phynox clip served as the reference standard. RESULTS: We found minimal magnetization and a significant reduction in image artifacts with the titanium clip as compared with the Phynox clip. CONCLUSION: The titanium clips improve image quality, biocompatibility, and patient safety in medical MR applications.

Aneurysm↗
PubMed1997

Nonuniformity intrinsic flood artifact caused by point-source syringe needle.

UNLABELLED: The purpose of this study was to investigate the cause of a nonuniformity artifact seen on an intrinsic flood. METHODS: Intrinsic floods were acquired on three different cameras using a point source in a 1-cc syringe, with and without a needle attached. Floods were obtained with the syringe placed perpendicular and parallel to the camera face. RESULTS: A nonuniformity artifact was evident if a syringe with a needle was placed perpendicular to the crystal face. CONCLUSION: If a syringe is used as a point source during the acquisition of an intrinsic quality control flood, the needle should not be placed perpendicular to the camera face.

Artifacts↗
PubMed1998

Importance of correct interpretation of postmortem artifacts in medicolegal autopsies.

PURPOSE: To study whether various injuries labelled as antemortem are in fact postmortem artifacts. STUDY SUBJECTS: 780 postmortems conducted in mortuary of S.M.C. Karachi from 1-1-95 to 20-9-95. MAIN FINDINGS: Out of 780 autopsies, 229 showed postmortem artifacts which included decomposition in 78, animal and insects producing changes in 45, injuries due to rough handling in 40, breaking of rigor mortis and shifting of postmortem lividity during transportation in 37, iatrogenic fracture of skull during opening in 15, fractured ribs during resuscitation after death in 8 and exhumation producing fractures of bones in 6 bodies.

Artifacts↗
PubMed1998

An efficient method for correcting the edge artifact due to smoothing.

Spatial smoothing is a common pre-processing step in the analysis of functional brain imaging data. It can increase sensitivity to signals of specific shapes and sizes (Rosenfeld and Kak [1982]: Digital Picture Processing, vol. 2. Orlando, Fla.: Academic; Worsley et al. [1996]: Hum Brain Mapping 4:74-90). Also, some amount of spatial smoothness is required if methods from the theory of Gaussian random fields are to be used (Holmes [1994]: Statistical Issues in Functional Brain Mapping. PhD thesis, University of Glasgow). Smoothing is most often implemented as a convolution of the imaging data with a smoothing kernel, and convolution is most efficiently performed using the Convolution Theorem and the Fast Fourier Transform (Cooley and Tukey [1965]: Math Comput 19:297-301; Priestly [1981]: Spectral Analysis and Time Series. San Diego: Academic; Press et al. [1992]: Numerical Recipes in C: The Art of Scientific Computing, 2nd ed. Cambridge: Cambridge University Press). An undesirable side effect of smoothing is an artifact along the edges of the brain, where brain voxels become smoothed with non-brain voxels. This results in a dark rim which might be mistaken for hypoactivity. In this short methodological paper, we present a method for correcting functional brain images for the edge artifact due to smoothing, while retaining the use of the Convolution Theorem and the Fast Fourier Transform for efficient calculation of convolutions.

Artifacts↗
PubMed1981

Somatic growth failure in infants related to artifact and error.

Growth failure in infants may be diagnosed erroneously because of artifact, error, or both. Assuming that all full-term infants have the same gestational age creates an artifact that is confounded further by errors in measurement of birth length. Crown-heel lengths of 77 while full-term newborns born at the University of Kansas Medical Center, Kansas City, were plotted on standard National Center for Health Statistics postnatal growth chart percentiles appropriate for sex, both with and without regard for gestational age. By the end of the first postnatal year, significantly fewer downward shifts in the growth curves occurred when fetal age was considered in the location of birth percentiles, according to tables by Miller and Merritt. To avoid confusion in interpretation of downward shifts in infants' growth patterns, we recommend that accurate crown-heel lengths be obtained at birth and plotted according to gestational age whenever possible.

Body Height↗
PubMed1988

Gas chromatographic/mass spectrometric identification of chlorinated and oxygenated cyclohexene artifacts formed during the analysis of chlorinated water samples.

Chlorinated and oxygenated cyclohexene derivatives detected in methylene chloride extracts of chlorinated drinking water were demonstrated to be artifacts produced during sample preparation. Commercial methylene chloride contains cyclohexene as a preservative, and this reacted during the extraction/concentration process to produce microgram amounts of chlorocyclohexene, 2-chlorocyclohexanol, trans-1,2-dichlorocyclohexane, cyclohexenone and cyclohexenol. Quantitative analysis indicated that over 90% of the initial cyclohexene was consumed during the process. Dechlorination of drinking water with sodium arsenite significantly reduced but did not eliminate cyclohexene artifact formation.

Chlorine↗
PubMed1976

Potential artifact in measurement of left ventricular filling pressure with flow-directed catheters.

Artifactual pulmonary wedge pressure measurements were encountered during bedside use of Swan-Ganz catheters. These values were higher than pulmonary artery end diastolic pressure and devoid of typical phasic contours. Utilizing fluoroscopy these artifacts were reproduced by advancing the catheter tip 2-4 cm beyond the site of initial wedging and reinflating the balloon. Spurious increases of pulmonary wedge pressure of up to 15 mm Hg were thus obtained. In vitro catheter testing demonstrated overlapping of the catheter tip by the deformed balloon when it was fully inflated in a channel too small to accomodate it. These measurement artifacts are thus attributed to distal migration of the catheter tip into relatively small pulmonary artery branches and to subsequent occlusion of the catheter lumen by the balloon when it is reinflated. This can readily be avoided by routinely inflating the balloon with the minimum volume of air sufficient to yield a pulmonary wedge pressure tracing.

Blood Pressure↗
PubMed1978

Artifact production with micromanometers used to record intracardiac pressure and sound.

In horses experimental right and left heart catheterization using a catheter with two microtransducers 9 cm apart, usually in a transvalval position produced pressure and sound artifacts that confounded the diagnosis. Most were probably due to malpositioning resulting in movement through a valve during recording or impingement on the valve cusps or the chordae tendineae or lodgement in the apex of the heart. The recognition of these artifacts is particularly important in studies of large animals in which catheter siting cannot be monitored by radiography.

Animals↗
PubMed1988

Interval-coded texture features for artifact rejection in automated cervical cytology.

In order to improve the separation between abnormal cells and noncellular artifacts in the CERVIFIP automated cervical cytology prescreening system, 22 different object texture features were investigated. The features were all statistical parameters of the pixel density histograms or one-dimensional filtered values of central and border regions of the object images. The features were calculated for 231 images (100 cells and 131 artifacts) detected as Suspect Cells by the current CERVIFIP and were then tested in hierarchical and linear discriminant classifiers. After selecting the two best features for use in a hierarchical classifier, 83% correct classification was achieved. One of these features was specifically designed to remove poorly focused objects. With maximum likelihood discrimination using all 22 features, an overall correct classification rate of 90% was obtained.

Cell Division↗
PubMed2005

Discerning alumina ball wear from confounding metal transfer artifact.

On dismounting a ceramic femoral ball from its metal trunnion, there is usually a range of gray metallic bands transferred to the trunnion bore inside the ball. This creates an artifact that may compromise detection by weight of the exceedingly low wear rates of ceramic balls. The objective of this study was to compare the weight trending of the metal trunnions and their ceramic balls during conditioning studies. Our hypothesis was that a pretest conditioning protocol would eliminate or greatly reduce the metal transfer artifact. The balls and tapers were placed on a hip simulator under 300-600 load cycles but with no articulation. The balls were then dismounted from the trunnions, and both were cleaned and weighed. This was repeated 6-23 times. We developed a novel hydraulic method for dismounting balls from trunnions that proved to be safe and efficient. There was significant weight loss in the trunnions after the ball removal, but there was no corresponding weight gain in the alumina balls. The weight effect of the metal transfer appeared to have been removed from the balls with our standard cleaning procedures. Therefore, wear rates for alumina balls may be gravimetrically determined without compensating for the metal transfer from trunnion to ball.

Aluminum Oxide↗
PubMed2001

The relationship between dissociative tendencies and schizotypy: an artifact of childhood trauma?

Previous research has suggested a relationship between dissociative tendencies and schizotypy. This study sought to extend the previous work in two fundamental respects. First, explicit cognizance was taken of the multidimensionality of both dissociative tendencies and schizotypy. Second, the study examined the possibility that the observed correlation between dissociative tendencies and schizotypy is an artifact of the association between each of these personality domains and a history of childhood trauma. Australian adults (N = 116) were administered the Dissociative Experiences Scale, the Schizotypal Personality Questionnaire-Brief, and the Childhood Trauma Questionnaire. Hierarchical regression analysis revealed that both pathological and nonpathological dissociative tendencies were predicted by the dimensions of schizotypy, even after the contribution of childhood trauma had been removed. It is concluded that the relationship between dissociative tendencies and schizotypy is not an artifact of childhood abuse, but the clinical significance of this relationship remains to be established.

Adolescent↗
PubMed1981

Slice-thickness artifacts in gray-scale ultrasound.

We have become increasingly aware of the presence of a type of image artifact normally appearing in anechoic areas (eg, cyst, bladder, gallbladder) and giving the appearance of "sludge" or "debris." These artifactual echoes may be caused by the fact that the finite width of the transducer beam pattern produces a finite thickness of the patient scan plane. All echoes produced in this "thick" scan plane are misinterpreted as being due to structures in the normally assumed "thin" scan plane. We have tested and verified this hypothesis by simulating soft tissue interfaces with 400 grit silicon carbide sandpaper in a water tank. A set of clues are proposed to enable the rapid identification of these artifacts.

Diagnostic Errors↗
PubMed1985

Chemical-shift artifact correction scheme using echo-time encoding technique.

An investigation has been undertaken to study the effects of chemical shift on NMR image obtained by the projection reconstruction technique. Mathematical simulation studies indicate that chemical shift causes blurring in NMR images regardless of the image reconstruction technique. A systematic study of such artifacts is presented and possible correction schemes are proposed. Exemplary results with and without correction of the chemical-shift artifact and pulse schemes employed for projection reconstruction are presented. The present chemical-shift correction scheme is basically the same as a spectroscopic imaging technique such as the existing 4-D NMR imaging method except that the encoding steps required can be reduced substantially in the case of modest spectroscopic resolution.

Magnetic Resonance Spectroscopy↗
PubMed1999

Carbamylation of cysteine: a potential artifact in peptide mapping of hemoglobins in the presence of urea.

Peptide mapping is a useful technique for identifying posttranslational modifications. However, sometimes artifacts can be introduced during the mapping procedure which can be misleading in identifying the origin and nature of the modifications. During peptide mapping of unalkylated hemoglobins with Staphylococcus aureus V8 proteinase, we found a significant level of carbamylated cysteines. Carbamylation was not detected if recombinant human hemoglobin (rHb1.1) was alkylated prior to digestion. Our experiments indicated that this modification was an artifact of the digestion procedure in which the slightly acidic conditions promoted the reaction of cysteine sulfhydryls with residual cyanate derived from urea. Carbamylmercaptans were found to be stable under acidic conditions but were unstable in base. The extent of cysteine carbamylation can be moderated by the use of scavengers.

Alkylation↗
PubMed2002

A two-dimensional artifact from asynchronous decoupling.

Many heteronuclear NMR experiments employ decoupling to collapse the heteronuclear multiplet, using decoupling schemes with a periodic phase modulation like WALTZ, MLEV, or GARP. Because of the periodic nature of these schemes, cycling sidebands are generated, whose intensity can be strongly reduced by decoupling asynchronously. We show that the most common implementation of asynchronous decoupling on modern spectrometers is such that the cycling sidebands are subjected to a periodic modulation. For multidimensional experiments, this results in ridges that can seriously compromise the quality of the spectrum. Based on our model, the artifact in a 2D [(1)H]-(15)N NOE equilibrium experiment is simulated and it is shown that the artifact can be prevented by using synchronous decoupling.

Journal Article↗
PubMed1986

Artifacts in the assessment of metabolic gas exchange.

In mechanically ventilated patients metabolic gas exchange recordings are frequently influenced by routine patient therapy. In this study the influence of such artifacts is investigated and a method for automatic detection and suppression proposed. This method reduced the influence of artifacts on diurnal oxygen and carbon dioxide exchange from up to 10% to a maximum of 1%.

Adolescent↗
PubMed1981

Bacterial mesosomes: method dependent artifacts.

The occurrence of mesosomes was investigated during septum formation of vegetative and sporulating cells of Bacillus cereus. It has been demonstrated that bacterial mesosomes which are considered by numerous microbiologists as an integrated constituent of Gram positive bacteria, are in reality artifacts arising during the preparation for electron microscopy. The conventional fixation methods allowed enough time for the cytoplasmic membrane to react to the changed conditions and to form the typical pocket-like membrane invaginations. With cryofixation followed by freeze-substitution it was shown in ultrathin sections that mesosomes do not occur. The extremely rapid freezing and the substitution of the ice by an organic solvent containing the fixative prevented the formation of membraneous artifacts.

Bacillus cereus↗
PubMed1975

Dark neurons: a significant artifact: the influence of the maturational state of neurons on the occurrence of the phenomenon.

In cerebella of young rats, killed by decapitation, dark Purkinje cells were readily observed in animals from 16 days of age onward. In younger animals (from 0-12 days of age) these dark neurons were never observed. The author agrees with Cammermeyer and others that dark neurons are an avoidable artifact. The findings presented suggest, however, that the possibility of the occurrence of this type of artifact depends on the maturational state of the neurons concerned.

Age Factors↗