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At least 253 records · Page 14Linked to original sources
PubMed1993

An electrical artifact associated with the ERG-jet gold foil electrode.

PURPOSE: To examine a photoelectric artifact associated with the ERG-jet corneal contact lens electrode (Universe SA, La Chaux-de-Fons, Switzerland). METHODS: An artifact associated with the ERG-jet, gold foil corneal contact lens electrode was reproduced in vitro and in vivo using 50 msec light flashes. In vitro responses were examined using light flashes that varied in intensity, duration, and wavelength. Ionic strength of the bathing solution and temperature dependence were also examined. In vivo responses were compared to similarly recorded signals using the Burian-Allen bipolar electrode. RESULTS: The artifact is not apparent with microsecond light flashes, as with the Grass PS22 Photo-stimulator connected to a Ganzfeld. Longer light flashes and increasing light intensities, however, elicit graded responses that may resemble the late PIII component of the ERG in profile and in magnitude. The artifact varies with temperature, ionic concentration of the bathing medium, and wavelength of stimulating light. The artifact also varies in magnitude and polarity from one disposable electrode to the next. Light flashes of shorter wavelengths elicit greater responses than light flashes of equal radiant energy but of longer wavelengths. CONCLUSIONS: The artifact derives from electrode polarization occurring at the interface between the gold foil and its ionic medium. Caution is required when using light stimuli longer than 2-3 msec with this and similar types of intrinsically polarizable metal electrodes.

Artifacts↗
PubMed1993

Thermal artifacts and inter-gynecologist variation of laser cone biopsies of the cervix.

OBJECTIVE: To evaluate the extent of thermal artifacts and the inter-gynecologist variation in CO2 laser cone biopsies for cervical intraepithelial neoplasia (CIN) using high power density. METHODS: All 1180 histologic sections from 93 CO2 laser cone biopsies performed by nine gynecologists were evaluated by morphometry. Power density of 19,700 W/cm2 and spot size of 0.43 mm were used. The lengths of different epithelia, the distance from CIN to the excision margins, the thermal artifacts, and the extension of denudation were analyzed. Mean values and standard deviations were analyzed for all indices. The inter-gynecologist variation was analyzed using one-way analysis of variance, Tukey-Kramer Honestly Significant Difference test, and chi 2 contingency table analysis regarding cones classified as "good" or "not good". RESULTS: The mean length of analyzed surface per cone was 134 mm. In 3% of the sections, the sum of artifacts at the external excision margin exceeded the average "minimum free distance" from CIN to the margin (2.88 mm). At the endocervical excision margin, the free distance was exceeded in 17% of the sections. Eighteen percent of the cones had CIN at the excision margins, with no significant differences between gynecologists (P = .83). Differences existed between gynecologists regarding free minimum distance and minor thermal artifacts at the external margin, but when clinically relevant groups were applied, no significant differences were found (P > .05). CONCLUSION: We found that a high power density at CO2 laser cone biopsy resulted in specimens with minimal thermal artifacts compared to other authors who used low power density. No clinically relevant differences were found between the gynecologists regarding free margins or artifacts.

Adult↗
PubMed1991

Analysis of electro-oculographic artifact during vertical saccadic eye movements.

The analysis of vertical saccades by electrooculography (EOG) is limited by the presence of waveform artifacts that occur with both upward and downward saccades. The artifacts have been shown to increase the calculated velocities of upward saccades. For better evaluation of the nature of these artifacts, voluntary vertical saccades were recorded by EOG and magnetic search coil in five normal subjects and by EOG only in two patients who had previously undergone enucleation. All subjects demonstrated peaked EOG artifacts during vertical saccades. The amplitude of these artifacts was decreased but not completely eliminated by eyelid or eyeball fixation during the attempted saccade. Peak saccadic velocities were also decreased by eyelid fixation, but EOG measurements were generally less accurate than those obtained by search coil. There is evidence that these artifacts may be the result of a combination of eyelid electrical activity and resistance effects.

Electrooculography↗
PubMed1985

Comparison of dental xeroradiography and conventional film techniques for the frequency and significance of image artifacts.

The frequency of occurrence and the classification of image artifacts were determined during a large-scale clinical dental radiographic study in which two conventional film techniques and xeroradiography were used. The resultant 1,220 radiographic images were evaluated for the presence of image artifacts. A list of commonly occurring artifacts was compiled, and frequency tables were constructed. Xeroradiography showed more image artifacts and also a higher retake rate due to artifacts (17.4% for individual images and 4.3% when images were evaluated as part of a complete-mouth survey). Many of the artifacts observed for xeroradiography were related to incomplete operator training and unfamiliarity with specialized imaging techniques.

Adult↗
PubMed1976

Artifacts in portable electrocardiographic monitoring.

The development of portable ECG monitoring techniques has brought with it new insights into the electrical activity of the heart, and new problems in interpretation of artifacts. This article summarizes and classifies 15 different types of artifacts observed from dynamic electrocardiography. The artifacts appear partly as pseudo-arrhythmias mimicking supraventricular, ventricular, junctional, and dissociative rhythms. There are also non-arrhythmic artifacts which can be misleading in the interpretation of Q-waves, S-T-segments, and T-waves. Eight of the 15 artifacts have potentially serious consequences if not understood, and in 2 instances an artifact almost led to the unnecessary implantation of an artificial cardiac pacemaker.

Arrhythmias, Cardiac↗
PubMed1991

Automatic reduction of stimulus polarization artifact for accurate evaluation of ventricular evoked responses.

The ventricular evoked response, the cardiac depolarization generated in response to a pacing stimulus, is potentially useful as a sensor for rate responsive pacing and automatic threshold tracking. It is necessary to minimize the polarization artifact that results from pacing in order to sense cardiac depolarizations from the same electrodes that pace the heart. To accomplish this, a triphasic stimulus waveform consisting of precharge, stimulus, and postcharge was used. An algorithm was developed that introduced pacing stimuli during the refractory period of sensed beats, when cardiac depolarization could not occur by definition and polarization artifact could be evaluated. Precharge duration was varied until the amplitude of the polarization artifact was small compared to the evoked response. In 18 patients with temporary electrode catheters, polarization artifact was reduced from 6.8 +/- 3.4 mV to 1.9 +/- 1.1 mV after balancing (P less than 0.005). Initial precharge duration was 3200 mu sec and the mean final precharge duration was 3551 +/- 516 mu sec. In 14 patients with permanent bipolar pacing leads, polarization artifact was reduced from 3.2 +/- 3.5 mV to 0.7 +/- 0.6 mV (P less than 0.025). Final precharge duration averaged 3440 +/- 310 mu sec. Under a wide variety of pacing conditions, this algorithm simply and quickly reduces polarization artifact to a minimum to allow accurate analysis of evoked responses.

Algorithms↗
PubMedDate not supplied

Exposure artifacts in raster scanned equalization radiography.

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.

Humans↗
PubMed1983

Artifacts produced by moving grids.

Anti-scatter grids reduce the amount of secondary radiation contributing to the image and improve the signal-to-noise ratio. However, they may also lead to the creation of linear artifacts representing the shadows of the radiopaque septa. Grid motion perpendicular to the septa during the exposure can cause blurring of the artifacts; however, the wider septa of recently proposed grids increase the difficulty of suppressing the artifacts entirely. Physical characteristics which affect perceptibility of grid-line artifacts and the conditions needed for their elimination are analyzed. Sufficient grid movement can eliminate overlap artifacts, while synchronization of linear grid motion with exposure time can suppress artifacts for relatively small grid movements.

Technology, Radiologic↗
PubMed2001

Blink artifact elimination in electroencephalographic records based on discrete cosine transform domain modeling.

A method for eliminating blink artifacts that contaminate electroencephalographic (EEG) records is introduced. The proposed method enables a direct estimation of blink artifacts without the use of the simultaneously recorded electroculargraphic (EOG) signal. The estimation of blink artifacts in the EEG was achieved by modeling in the discrete cosine transform (DCT) domain. The DCT coefficients of the blink artifact were sufficiently represented by a system transfer function with a low model order of 4. Two cases were investigated: one was blink artifact elimination for the background EEG and the other was for the somatosensory evoked potentials. The effectiveness of the proposed method was demonstrated in an experimental study based on actual EEG data of 11 healthy subjects. The simplicity and effectiveness of the proposed method suggest that blink artifact elimination using DCT domain modeling can possibly be applied in various areas of neuroscience for improving EEG quality.

Adolescent↗
PubMed2000

Axis I and Axis II disorders in alcoholics and drug addicts: fact or artifact?

OBJECTIVE: It has been argued that Axis I and Axis II disorders diagnosed in substance users refer to substance-induced conditions rather than to independent psychiatric conditions; this argument will be referred to as the substance-related artifact hypothesis. Furthermore, Axis II symptoms co-occurring with Axis I disorders have been attributed to the contamination of personality assessment by mood and/or anxiety state effects (the trait-state artifact hypothesis). The present study is the first to prospectively examine the validity of these two hypothesized "artifacts" in substance users. METHOD: In 276 individuals (57.6% female) applying for substance use treatment, current substance use disorders, mood/anxiety disorders and Axis II disorders were diagnosed using semistructured interviews both at baseline and at 1-year follow-up. The substance-related artifact hypothesis is tested by examining the covariation between recovery from substance use disorders on the one hand and recovery from and/or improvement of mood/anxiety and Axis II disorders on the other hand. The trait-state artifact hypothesis is tested by examining the covariation between recovery from mood/anxiety disorders on the one hand and recovery from and/or improvement of Axis II disorders on the other hand. RESULTS: Recovery from substance use disorders covaried with recovery from and improvement of mood/anxiety disorders, but not with recovery from or improvement of Axis II pathology. Furthermore, recovery from mood/anxiety disorders covaried with recovery from and improvement of personality disorders, in particular Cluster C disorders. CONCLUSIONS: Results from this study suggest that mood/anxiety disorders, but not personality disorders, diagnosed among people with substance use disorder may partly reflect substance-related artifacts. Furthermore, this study provides evidence for the contention that semistructured interview assessment of Axis II, at least without inquiry on an item-by-item basis, is susceptible to contamination by mood/anxiety state effects.

Adult↗
PubMed1989

MR imaging artifacts of the axial internal anatomy of the cervical spinal cord.

Transverse scans of the spinal cord routinely demonstrate signal variations related to the internal anatomy of the cord that do not accurately conform to histologic cross sections. This study evaluates the MR appearance of the axial anatomy of the spinal cord and provides correlation to histologic sections as a means to understand this discordance so that disease can be recognized more readily. Short TR/TE spin-echo studies, cardiac-gated multiecho spin-echo studies, and gradient-refocused-echo studies of normal excised human spinal cords, a normal volunteer, and gelatin phantoms were obtained by using the same imaging parameters at 1.5 T. Imaging artifacts were further investigated by using both a 128 x 256 and 256 x 256 matrix with a varying phase-encoded axis. Histologic sections of the excised cords, which were stained for myelin, iron, and cell bodies (Nissl), were used for correlation to the images. We found that significant Fourier truncation and partial-volume imaging artifacts modulated the MR display of the cord. On short TR/TE images a ring of high signal at the periphery of the cord was due to a truncation artifact. The appearance of the central portions of the gray and white matter was affected variably by partial-volume averaging depending on the matrix size. White-matter tracts of the cord were always lower in signal than was the gray matter on all pulse sequences. This finding was not due to iron deposition or CSF motion artifacts. We suspect that this probably was related to dense, longitudinal organization of spinal tracts and resultant anisotropy of water molecule motion similar to that seen in the pyramidal tracts, tendons, and ligaments. We recommend the use of a 128 x 256 matrix with two averages (four excitations) when obtaining axial scans of the spinal cord in living subjects. Although truncation artifacts diminish image quality, the quality is superior to that of images obtained with a 256 x 256 matrix, in which longer scanning times result in motion artifacts and reduced signal to noise.

Humans↗
PubMed1984

Comparison of the efficiency of various criteria for artifact rejection in the recording of auditory brain-stem responses (ABR).

Artifact rejection using various criteria has not yet been investigated comparatively in the determination of auditory brain-stem responses (ABR). The aim of this paper is to test the efficiency of three different criteria of artifact rejection: the 'level' criterion, the 'amplitude histogram' criterion, and the 'power' criterion, and to compare their practical applicability. With regard to the identification of the single waves of ABR (percentage frequency of their appearance) and their amplitudes without and with artifact rejection, it can be shown that the frequency of appearance increases severalfold when one of the artifact rejection criteria is used. The difference between amplitude means with artifact rejection (all three criteria) and those without artifact rejection is significant on the 5% level for waves I, II, and III and on the 1% level for wave V. When the three criteria are compared with regard to the amplitude means of the individual waves, it can be shown that the best results are obtained, when the 'level' criterion is used, then follows the 'power' criterion and third is the criterion of 'amplitude histogram'. The differences, however, are not significant. With reference to the 'level' criterion used, our investigation proved that the more complicated 'amplitude histogram' and 'power' criteria are not more efficient.

Adult↗
PubMed1998

Blister artifact formation due to organic solvent effects on Spurr's epoxy resin semithin sections.

Wrinkles and air bubble artifacts may occur when preparing slides of semithin sections (0.5 microm) from blocks embedded in different resins. More than aesthetically annoying, wrinkles and air bubble artifacts may prohibit study of small structures. Present observations suggest that organic solvent based mounting media may interact with the resin of the section. This sometimes causes wrinkles and air bubble artifacts in the sections that degrade the quality of light microscope images. We compared the quality of semithin sections of several tissues in different resins using various types of mounting media. We observed that sections from Spurr's resin have many more artifacts. In particular, small, 2-10 microm round or oblong blister-like artifacts often plague our Spurr's resin sections. We demonstrate that Spurr's resin sections react with toluene and xylene in organic solvent based mounting media forming blisters, while sections from Araldite and L. R. White do not. We suggest combinations of embedding and mounting media for successful preparation of semithin sections for light microscopy without wrinkles, blisters, or air bubble artifacts.

Animals↗
PubMed1989

[Artifacts in ultrasonic diagnosis].

Due to facts of the wave theory, to properties of ultrasound-systems and to peculiarities of the examined organs and tissues artifacts may influence the image-formation in diagnostic sonography. In diagnostic ultrasound five types of artifacts are common: --Displaying of nonstructural echo signals (reverberation and reflection) --Removal of real structural echo signals from the display (tissue-attenuation and acoustic shadowing) --Displacement of echo signals on the display (refraction and beamwidth-artifact) --Distortion of echo signals (shape distortion-artifact, bands, gray-scale-contouring and blobby dots) --Distortion of the organ dynamics on the display (reverberation or "ring-around" and "herbie") The understanding of the mechanisms behind their production allows recognition of artifacts and avoids misinterpretations and incorrect diagnoses. Moreover, it helps to prevent the production of artifacts, e.g. by proper gain-control-setting, adjusted focussing, etc.; it also may, if properly evaluated, reveal further information which can be used for diagnostic purposes (e.g. nature and geometry of interfaces, content of cysts, etc.).

Animals↗
PubMed1989

[Computed tomography of the kidney with diuretics--a method for avoiding artifacts due to nonionic contrast media].

We devised a method for avoiding beam-hardening artifacts, which interfere with enhanced CT images of kidney due to nonionic contrast medium. The radiographic effect and the frequency of beam-hardening artifacts on enhanced CT of kidney were studied by prospective comparison among three groups: a group of 20 patients examined with furosemide (f-d. CT), a group of 20 patients examined without diuretics (non-d. CT) and a group of 20 patients examined after water intake (w-d. CT). In all patients of f-d. CT group, the renal parenchyma from the cortex to the papilla was almost evenly enhanced, free from artifacts. The density of the renal papilla and pelvis in non-d. CT and w-d. CT groups was significantly higher than that in f-d. CT group, and artifacts were also observed in 14 (70%) of non-d. CT group and 12 (60%) of w.d. CT group, respectively. Satisfactory CT of kidney free from artifacts was obtained by f-d. CT, providing easy evaluation of renal pelvic or peripelvic lesions. In conclusion, this technique can be used in those pathologic cases of renal pelvis or peripelvic region, that are not clear on routine CT because of artifacts.

Adult↗
PubMedDate not supplied

Analytical controls in drug metabolic studies. II. Artifact formation during chloroform extraction of drugs and metabolites with amine substituents.

Chemical artifacts are readily produced during chloroform extractions of drugs and metabolites with amine substituents by the reaction of chloroform contaminants, phosgene and ethyl chloroformate, to form carbamoyl chlorides and carbamates. Chloroform obtained from three different suppliers was examined with regard to the effects of preservatives and exposure to air on the quantity and nature of these contaminants. Extractions with chloroform obtained from a supplier's sealed bottle and containing ethanol preservative produced the least amount of artifact. With previously opened bottles (prior exposure to air, open), the amount of artifact formation rose substantially. Chloroform without preservative or with a nonpolar hydrocarbon preservative likewise produced large amounts of artifacts during extraction. Attempts to purify chloroform showed that distillation was ineffective for the removal of phosgene or ethyl chloroformate, whereas their effective removal was accomplished by solvent elution through a column of activated alumina or upon standing over calcium hydroxide powder. Possible artifact formation must be considered in drug-metabolism studies and appropriate controls included for the detection and elimination of chemical artifacts.

Amines↗
PubMed1998

In situ temperature measurements with thermocouple probes during laser interstitial thermotherapy (LITT): quantification and correction of a measurement artifact.

BACKGROUND AND OBJECTIVE: The purpose of this work was to quantify the magnitude of an artifact induced by stainless steel thermocouple probes in temperature measurements made in situ during experimental laser interstitial thermo-therapy (LITT). A procedure for correction of this observational error is outlined. STUDY DESIGN/MATERIALS AND METHODS: A CW Nd:YAG laser system emitting 20W for 25-30 s delivered through a fiber-optic probe was used to create localized heating. The temperature field around the fiber-optic probe during laser irradiation was measured every 0.3 s in air, water, 0.4% intralipid solution, and fatty cadaver pig tissue, with a field of up to fifteen needle thermocouple probes. RESULTS: Direct absorption of Nd:YAG laser radiation by the thermocouple probes induced an overestimation of the temperature, ranging from 1.8 degrees C to 118.6 degrees C in air, 2.2 degrees C to 9.9 degrees C in water, 0.7 C to 4.7 C in intralipid and 0.3 C to 17.9 C in porcine tissue after irradiation at 20W for 30 s and depending on the thermocouple location. The artifact in porcine tissue was removed by applying exponential and linear fits to the measured temperature curves. CONCLUSION: Light absorption by thermocouple probes can induce a significant artifact in the measurement of laser-induced temperature increases. When the time constant of the thermocouple effect is much smaller than the thermal relaxation time of the surrounding tissue, the artifact can be accurately quantified. During LITT experiments where temperature differences of a few degrees are significant, the thermocouple artifact must be removed in order to be able accurately to predict the treatment outcome.

Animals↗
PubMed2000

Reduced aliasing artifacts using variable-density k-space sampling trajectories.

A variable-density k-space sampling method is proposed to reduce aliasing artifacts in MR images. Because most of the energy of an image is concentrated around the k-space center, aliasing artifacts will contain mostly low-frequency components if the k-space is uniformly undersampled. On the other hand, because the outer k-space region contains little energy, undersampling that region will not contribute severe aliasing artifacts. Therefore, a variable-density trajectory may sufficiently sample the central k-space region to reduce low-frequency aliasing artifacts and may undersample the outer k-space region to reduce scan time and to increase resolution. In this paper, the variable-density sampling method was implemented for both spiral imaging and two-dimensional Fourier transform (2DFT) imaging. Simulations, phantom images and in vivo cardiac images show that this method can significantly reduce the total energy of aliasing artifacts. In general, this method can be applied to all types of k-space sampling trajectories.

Algorithms↗