Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “artifacts”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 793 records · Page 44Linked to original sources
PubMed1985

Artifacts in the measurement of skin temperature under infant radiant warmers.

All skin temperature probes measure, to some extent, operative temperature as well as skin temperature, and thus artifactually measure a temperature different from true skin temperature. To assess the magnitude and direction of these artifacts in the measurement of surface temperature in radiant warmers designed for human infants, the artifactual deviation of measured surface temperatures from mean surface temperature was determined under a short-wavelength warmer and a long-wavelength radiant warmer, using a copper ball as an experimental model. The measurements were made using both a disk-shaped thermistor and a tubular thermistor. All measurements were made near the top of the hemisphere of the ball facing the heating element of the warmer. In all cases, the average artifact was negative. That is, even on the surface of the ball near the radiant heat source, the surface temperature probes recorded an artifactually low temperature. In the analogous clinical setting, a somewhat larger negative artifact would be expected.

Biomedical Engineering↗
PubMedDate not supplied

Ferromagnetism and magnetic resonance artifacts of platinum embolization microcoils.

We performed in vitro tests of ferromagnetism of platinum microcoils of two manufacturers. In addition, we performed in vitro magnetic resonance imaging (MRI) on these two devices to determine their levels of magnetic susceptibility artifact production. We found that both devices were nonferromagnetic and produced a very low level of artifact during MRI. In vivo MRI of a dog and 2 patients having previous placement of platinum microcoils was performed without coil migration or significant artifact production. Platinum microcoils are highly MR-compatible.

Adult↗
PubMed2000

Artifacts in CSI-measurements caused by the drift of the static magnetic field.

In chemical shift resolved spectroscopic imaging (CSI) temporal changes in the static magnetic field (drift) can lead to distortions of the phase encoding process. This can result in localization artifacts. The extent of the artifact depends on the size of the drift, the number of acquisitions, as well as on the combination of the size of the field of view and the number of phase encoding gradient steps. Furthermore, it is affected by the succession of the phase encoding gradients. Precautions are described which allow substantial minimization of the artifact.

Humans↗
PubMed1991

Artifacts in urinary tract ultrasonography.

Ultrasound is the only technique that uses artifacts in diagnosis. "Good through transmission" and a "refractive artifact" indicate fluid. Acoustic shadowing can be produced by different tissues leading to different types of shadows and specific diagnoses. Fat produces a decrease in the speed of sound as compared with soft tissue leading to the writing of structures behind fat distal to their actual position. Other artifacts are also described.

Female↗
PubMed1978

A sample and hold amplifier system for stimulus artifact suppression.

A sample and hold amplifier system has been described which is capable of eliminating stimulus artifacts from a variety of biological recordings which would otherwise be impossible to interpret during electrical stimulation. Factors contributing to the prolongation of stimulus artifact are discussed in relation to the design requirements of this system. The application of this artifact suppression circuit to monitoring EEG seizures during electrical stimulation is demonstrated.

Amplifiers, Electronic↗
PubMed1982

Analog delay line artifact rejector for evoked potential studies.

A true artifact rejector which utilizes a bucketbrigade delay line is described. The delay line enables scanning of all the data in the analysis period prior to its inclusion in the average. The device is small in size, independent of the averager, and the total cost of components is under $100. This artifact rejector is compatible with any averager. Artifact rejection can be according to excessive amplitude, as described in this version, or according to externally applied signals. In addition, by a minor change in the interference detector module, rejection could be according to other criteria, such as frequency contents. The utility of the device is demonstrated on records of auditory brain stem evoked potentials.

Analog-Digital Conversion↗
PubMed1983

Removal of eye movement and ECG artifacts from the non-cephalic reference EEG.

A method is described that automatically eliminates eye movement artifacts from EEG records and creates an extracranial reference electrode in one single process. The usefulness of this method is illustrated for both standard EEG recording as well as for CNV and P300 potentials. The artifact signals are measured with a special set of electrodes and are combined in order to subtract the artifacts from contaminated EEG records. The subtraction ratios are determined as those that minimize the variance in the result corrected EEG signal.

Contingent Negative Variation↗
PubMed1983

A new method for off-line removal of ocular artifact.

A new off-line procedure for dealing with ocular artifacts in ERP recording is described. The procedure (EMCP) uses EOG and EEG records for individual trials in an experimental session to estimate a propagation factor which describes the relationship between the EOG and EEG traces. The propagation factor is computed after stimulus-linked variability in both traces has been removed. Different propagation factors are computed for blinks and eye movements. Tests are presented which demonstrate the validity and reliability of the procedure. ERPs derived from trials corrected by EMCP are more similar to a 'true' ERP than are ERPs derived from either uncorrected or randomly corrected trials. The procedure also reduces the difference between ERPs which are based on trials with different degrees of EOG variance. Furthermore, variability at each time point, across trials, is reduced following correction. The propagation factor decreases from frontal to parietal electrodes, and is larger for saccades than blinks. It is more consistent within experimental sessions than between sessions. The major advantage of the procedure is that it permits retention of all trials in an ERP experiment, irrespective of ocular artifact. Thus, studies of populations characterized by a high degree of artifact, and those requiring eye movements as part of the experimental task, are made possible. Furthermore, there is no need to require subjects to restrict eye movement activity. In comparison to procedures suggested by others, EMCP also has the advantage that separate correction factors are computed for blinks and movements and that these factors are based on data from the experimental session itself rather than from a separate calibration session.

Blinking↗
PubMed1985

Artifacts in ambulatory cassette electroencephalograms.

Most artifacts in ambulatory electroencephalograms (AEEGs) are similar to those seen on conventional electroencephalograms (CEEGs) and can be identified as such. Some artifacts may simulate epileptiform or slow wave EEG activity and may occur asymmetrically or focally. We have described the use of a dual write-out method for identifying and detecting the source of artifacts in AEEGs. This technique has improved the quality of AEEGs and facilitated interpretation.

Adolescent↗
PubMedDate not supplied

False-positive artifacts of tracer strategies distort autonomic connectivity maps.

The widespread use of new axonal transport tracing techniques in the ANS has resulted in substantially revised and amended descriptions of ANS organization. The present review suggests, however, that at least some of the results on which proposed revisions of ANS anatomy have been based have incorporated artifacts and therefore should be cautiously interpreted. The peripheral nervous system and viscera are composed in part of connective and endothelial tissues that are porous or 'leaky' to solutes with appropriate chemical characteristics, including the major tracer compounds. As a result, several extra-axonal routes for redistribution of label from the application site into other tissues are present. These include (1) diffusion through tissue membranes to enter directly adjacent tissues and (2) leakage into extracellular fluids within the body cavity, vasculature, lymphatics, exocrine ducts, or organ lumens to migrate to more distant tissues. As a consequence of the extreme sensitivity of the methods used, such redistribution of even minute amounts of label can produce false positives. Review of autonomic neuroanatomy suggests additional mechanisms, including tracer uptake by fibers of passage, can produce artifactual staining. Based on these surveys of tissue composition, tracer characteristics and sources of artifact, experimental controls and criteria for identifying and avoiding labeling artifacts are described. Since no single procedure is foolproof for ANS experimentation, the routine application of multiple controls, particularly ones which restrict or prevent tracer diffusion, are needed.

Animals↗
PubMed1995

Brain-stem auditory evoked potential monitoring. Variations of stimulus artifact in brain death.

Brain-stem auditory evoked potentials (BAEPs) were recorded in 20 subjects with brain death (mean age, 33.2 +/- 15.1 years) and 20 healthy volunteers (mean age, 29.8 +/- 6.8 years). Brain death was due to head injury (n = 14), encephalitis (n = 3), brain-stem hemorrhage (n = 1), cerebellar hemorrhage (n = 1) or cerebral infarction (n = 1). The presence, latency and amplitude of the individual BAEP components and variations of the stimulus artifact were evaluated. The mean (+/- S.D.) amplitude of the stimulus artifact was 0.26 +/- 0.12 microV in the brain-dead subjects and 0.09 +/- 0.05 microV in the control group (P < 0.001, t test). The causes of the phenomenon of increasing stimulus artifacts in the evolution of brain death remain unclear.

Acoustic Stimulation↗
PubMedDate not supplied

The removal of the eye-movement artifact from the EEG by regression analysis in the frequency domain.

A new method to remove the eye-movement artifact from the electro-encephalogram (EEG) is described. It is based on complex regression analysis. Transfer of eye-movement activity to EEG can have frequency dependent amplitude and phase characteristics. The proposed method is suitable for handling such transfer because the regression formula is used in the frequency domain. The method is demonstrated with artificial signal-in-noise EOG (electro-oculogram) and EEG series. In the EEG noise an event related potential (ERP) is buried as a constant signal and in the EOG noise a changing EOG response (saccadic eye-movement) is simulated before adding the whole series to the EEG series. Also decreasing levels of transfer from EOG on EEG leads are simulated as the EOG artifact diminishes from the frontal to the occipital area. Because of the possible frequency dependent phase characteristics also a 24 msec time-shift of the EOG is simulated. The complex regression coefficient (P(jw)) of the EOG and EEG series is first calculated and then 'common' regression is removed from the EEG. To do this the estimated P(jw) is tested for significance with the F-statistic and significant EOG activity is subtracted in the frequency domain from the EEG on a single trial base. Then each EEG record is inversely transformed to the time domain. It was found that the complex P(jw)s as used in the subtraction formula, corrects very accurately the influence of the EOG artifact on EEG activity. Finally an application of the method in a real life situation is reported.

Electroencephalography↗
PubMed1989

Correlation artifacts in speed of sound estimation in scattering media.

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 are a 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.

Computer Simulation↗
PubMed1985

Morphological artifacts induced in intracellularly stained neurons by dehydration: circumvention using rapid dimethyl sulfoxide clearing.

In order to observe the fine details of intracellularly stained neurons in brain slices the slices must be cleared of opaque matter. This clearing process involves dehydration of the slice, which typically results in significant shrinkage of the cleared tissue. However, how this shrinkage affects neuronal morphology has not been demonstrated to date. In this paper we detail the artifacts induced in the morphology of stained neurons by this clearing process. During dehydration-induced shrinkage of the brain slices, neurons stained with the water-soluble dye, Lucifer yellow, demonstrated a dramatic decrease in size to less than two-thirds of their original dimensions. In contrast neurons stained with the horseradish peroxidase/diaminobenzidine reaction-product did not shrink with the slice; instead the dendrites bent and curled during dehydration with no loss in cell-soma size. We have managed to circumvent these artifacts by using as a clearing agent the solvent dimethyl sulfoxide, which is miscible in both aqueous and organic phases. This solvent will clear tissue slices without inducing the concomitant artifacts caused by tissue shrinkage occurring with the alcohol-dehydration process.

Animals↗
PubMed1986

Reducing motion artifacts in two-dimensional Fourier transform imaging.

The effects of motion in two-dimensional Fourier transform imaging (2DFT) are considered. Specific calculations describing the case of periodic motion are presented. The results predict the commonly seen artifact of image replication, sometimes referred to as ghosting. Expressions for both position and amplitude of these ghosts are derived. Simulated examples illustrate the image degradation for pulsatile flow and in plane motion. Several methods of reducing motion artifacts are then suggested. These include: randomization of views, averaging views, matching repeat times to the respiratory period, hybrid imaging, ROPE and COPE. The latter two methods reorder the data acquisition to destroy the coherence of the motion. They do not increase the data acquisition time and promise to be part of the standard approach to remove motion artifacts. The final step in actually recovering ideal resolution can be accomplished by using a model of the motion and a generalized transform inversion technique.

Fourier Analysis↗
PubMedDate not supplied

The motion artifact suppression technique (MAST) in magnetic resonance imaging: clinical results.

The Motion Artifact Suppression Technique (MAST) is a method which uses a series of gradient echos that are computed to cancel velocity, acceleration and pulsatility components of involuntary motion in MR imaging. A total of 916 patient studies were performed over a nine month period using MAST sequences with a TE 40, 60, 80, 100, 120, and 26/112. There was considerable improvement in long TR, long TE images. Cerebrospinal fluid flow artifacts were reduced. Body and spine images had reduced flow and respiratory artifacts. Spin rephasing in blood vessels caused increase intraluminal signal. This might be useful for cardiovascular imaging.

Blood Circulation↗
PubMed1990

Angiographic artifacts that simulate arterial pathology in acute trauma.

Films from 246 angiograms performed for acute trauma were reviewed for artifacts that mimic arterial pathology. The population studied was young (mean age 31.8 years), and preexisting arterial disease was uncommon. Thirty patients (12%) exhibited 35 artifactual abnormalities. Artifacts included stationary wave formation (15 patients), admixture in the leading edge of the contrast column (7 patients) or streaming from the inside aspect of an arterial curve (13 patients), Mach bands (8 patients), and abnormal densities caused by the mishandling of film (1 patient) or discharge of static electricity (1 patient). These artifacts have typical morphologic appearances and locations that allow differentiation from pathological processes that manifest as intraluminal filling defects or arterial wall irregularity.

Adolescent↗
PubMed1994

Pseudofractures of the mandible secondary to motion artifact.

The case of a patient with a false-positive fracture on the panoramic view of the mandible is presented. The patient motion produced a spurious image that perfectly mimicked a fracture without any evidence of motion. To better assess motion artifact, panoramic views of a "phantom" human skull were developed with movement during the exposure. These radiographs were analyzed with the assistance of a radiologist, and diagnostic features of motion artifact are discussed. Some radiographs were created by movement that mimicked fractures without the telltale signs of motion artifact. These "motion pseudofractures" are diagnosed clinically if the examiner knows that motion can mimic fractures, and all x-ray findings are carefully correlated with clinical findings. Diagnosis of a motion pseudofracture will avoid the additional expense and time of a specialty consultation.

Adult↗