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PubMed1986

Pacemaker malfunction: fact or artifact?

In summary, the present examples illustrate how pacemaker malfunction can be simulated by the sources of artifact produced or detected by the monitoring equipment. This form of pseudopacemaker malfunction remains a common cause of mistaken diagnosis of pacemaker malfunction. A thorough understanding of the examples outlined above should help distinguish true pacemaker malfunction from pseudopacemaker malfunction produced by artifact.

Amplifiers, Electronic↗
PubMed1987

Rotational artifact in phase imaging of cardiac scans: potential pitfalls in diagnosis.

In the past few years, we have occasionally observed linear bands in the phase images of gated cardiac blood-pool scans along the interventricular septum region among patients with normal septal motions. Our retrospective study investigated the cause of out-of-phase bands of 12 patients. We documented through review of cines, computer analysis of gated cardiac blood-pool scintigraphy data, and correlation with echocardiograms that this phenomenon was artifact introduced by rotational movements of the heart. It is important for nuclear physicians to recognize this rotational artifact on the phase analysis image in order to avoid the erroneous misdiagnosis of wall motion abnormalities of the septum.

Adult↗
PubMed1986

Lightning artifact in the EEG.

Lightning is highly prevalent in South Florida. The artifact caused by lightning in EEG recordings is of variable duration and seen as abrupt deflection of pens, sometimes followed by sustained pen drift and slow recovery mimicking amplifier overload as caused by rapid unplugging and plugging of the equipment power cable from the wall outlet. Since this artifact was associated to hospital light flickering and was recorded independent of machine location and orientation, we believe it is secondary to extreme brief Mains voltage fluctuations, probably due to horizontal lightning electric field effects rather than radio or electromagnetic interference generated by lightning.

Electroencephalography↗
PubMedDate not supplied

Posterior lobe of the pituitary: identification by lack of chemical shift artifact in MR imaging.

The posterior aspect of the normal sellar content usually displays high intensity signal on T1-weighted images. The shape, size, and location of this high intensity seem to be compatible with the posterior lobe of the pituitary gland. But fatty tissues such as intrasellar fat pad or fatty marrow of the dorsum sellae or both must be excluded as other possible sources of this high intensity signal. Two sellar phantoms were prepared. Both included high intensity posterior parts, one due to high concentration of a paramagnetic ion and the other due to fat. Magnetic resonance imaging of these phantoms showed that the fatty component was accompanied by distinct chemical shift artifacts in a predictable way. The absence of chemical shift artifact in the sellar content of normal volunteers excluded the fatty tissue as representing the high intensity posterior part. The high intensity posterior part of the normal sellar content appears to represent the posterior lobe of the pituitary gland.

Adipose Tissue↗
PubMed1980

A search for protein cores in chromosomes: is the scaffold an artifact?

A protein chromosome scaffold structure has been proposed that acts as a structural framework for attachment of chromosomal DNA. There are several troubling aspects of this concept: (1) such structures have not been seen in many previous thin-section and whole-mount electron microscopy studies of metaphase chromosomes, while they are readily seen in leptotene and zygotene chromosomes; (2) such a structure poses problems for sister chromatid exchanges; and (3) the published photographs show a marked variation in the amount of scaffold in different whole-mount preparations. An alternative explanation is that the scaffold in whole-mount preparations represents incomplete dispersion of the high concentration of chromatin in the center of chromosomes, and when the histones are removed and the DNA dispersed, the remaining nonhistone proteins (NHPs) aggregate to form a chromosome-shaped structure. Two studies were done to determine if the scaffold is real or an artifact: (1) Chinese hamster mitotic cells and isolated chromosomes were examined using two protein stains -EDTA-regressive staining and phosphotungstic acid (PTA) stain. The EDTA-regressive stain showed ribonucleoprotein particles at the periphery of the chromosomes but nothing at the center of the chromosomes. The PTA stain showed the kinetochore plates but no central structures; and (2) isolated chromosomes were partially dispersed to decrease the high concentration of chromatin in the center of the chromosome, then treated with 4 M ammonium acetate or 2 M NaCl to dehistonize them and disperse the DNA. Under these circumstances, no chromosome scaffold was seen. We conclude that the scaffold structure is an artifact resulting from incomplete dispersion of central chromatin and aggregation of NHPs in dehistonized chromosomes.

Animals↗
PubMed1982

Diesel particle and organic emissions: engine simulation, sampling, and artifacts.

Several working hypotheses can be drawn relative to measuring diesel exhaust particles and organics. They are: 1. Passenger car dynamometer simulation and driving cycles are adequate for determining mass emission rates. The choice of a simulation condition appears to make little difference. Evidence for trucks is fragmentary, but high load freeway driving produces especially high particle emissions. 2. Sampling of particles and organics can be done in a variety of ways. Since most sampling systems yield similar results, the choice is not critical. If measuring mutagenic agents is the issue, then the distribution between gas and particle phase is also not critical. 3. Artifactual generation of mutating agents in sampling seems to be relatively unimportant. Filter media studies are negative, with respect to artifacts. Although there is evidence of artifact formation from NO2 concentrations above 5 ppm, this condition is not generally present under normal sampling conditions. Consequently, in the context of laboratory studies of diesel emissions, it appears difficult to choose conditions that will produce totally invalid samples. Differences in particle emission factors from various vehicle types are substantial, however, and these influences on air quality are important.

Air Pollutants↗
PubMed1984

The modality shift effect in schizophrenia: fact or artifact?

We investigated whether the disproportionate slowing of schizophrenic patients on cross-modal relative to ipsimodal sequences in a reaction time task ("modality shift effect") could be attributed to a psychometric artifact, as implied by Chapman and Chapman. Fifteen schizophrenic patients (Research Diagnostic Criteria) and 50 normal controls with no current or past history of psychiatric disorder were tested. Subjects made an identical finger-lift response to brief duration light and sound stimuli of different intensities presented in quasi-random order. The major finding was that psychometric artifact could not account for the disproportionate slowing of the reaction time of schizophrenic patients since the reliabilities and variances of the cross-modal and ipsimodal conditions did not differ in normal controls. Furthermore, the modality shift effect was highly significant for reaction times to both sound and light and for all intensities. Findings were the same when the schizophrenic patients were compared to a matched subgroup of slow-responding normal controls.

Cues↗
PubMed1983

The rejection of noncellular artifacts in Papanicolaou-stained slide specimens by an automated high-resolution system. Identification of important cytometric features.

The important cytodiagnostic features that permit discrimination of typical cell types by high-resolution image analysis and pattern recognition techniques have been previously studied in detail. An automated system for the diagnosis of Papanicolaou-stained specimens must also deal, however, with the "real world" of extraneous noncellular artifacts and debris found on every slide. Features that are ideal for the separation of typical normal and abnormal cells may not be adequate by themselves to reject these objects. A new set of discriminatory features must be found. In order to identify those features, a large set of images acquired using the TICAS high-resolution television rapid-scanning system was analyzed and studied. These images, from a variety of slide types, included normal cells, abnormal cells and noncellular artifacts identified by low-resolution preprocessing logic as suspicious enough to warrant high-resolution study. The results indicate that the more important features for such discrimination are not those traditionally important in distinguishing abnormal from normal cells but include color relations, shape measures, boundary properties and texture features.

Cell Separation↗
PubMed1982

Creatine kinase isoenzymes in neonate plasma by cellulose acetate electrophoresis: albumin and adenylate kinase artifacts.

Patterns of creatine kinase (CK, EC 2.7.3.2) isoenzymes were studied in apparently healthy one- to 10-day-old neonates, by use of a sensitive fluorescent staining method with Sclavo CK-F/6001 reagent. Mean activities of CK3 (MM, 105 U/L), CK2 (MB, 6.8 U/L), CK1 (BB, 11 U/L), adenylate kinase (EC 2.7.4.3) anodal to CK3, and a fluorescent albumin artifact were found. Pooled plasma from neonates is recommended as a control because it defines the albumin artifact and approximates the activity of CK2 that must be observed after proper staining before a diagnosis of myocardial infarction can be made.

Adenylate Kinase↗
PubMed1982

Measuring the average evoked response to light flashes: the contribution of eye-blink artifact to augmenting-reducing.

There have been numerous reports relating individual differences in stimulus intensity control to psychopathology and personality. Most of these studies record the averaged evoked response (AER) to light flashes of different brightness and assess the relationship between response amplitude and stimulus intensity. The present investigation used procedures commonly employed in these studies to examine the effects of eye blinks on the AER. Twenty normal subjects were tested twice over a 1-week interval while the AER and electroocculographic (EOG) response generated by a blink were recorded. The averaged EOG was digitally subtracted from the AER to yield a blink-corrected AER. Various comparisons of amplitude measures derived from corrected and uncorrected AERs and the averaged EOG revealed that blinking contributed a pronounced artifact that tended to reduce the magnitude of AER amplitude, especially to the more intense stimuli. These findings raise questions about the validity of interpretations drawn from studies of AER augmenting-reducing, very few of which control for eye-blink artifact. The linearity of the amplitude-intensity relationship for each subject was also assessed. This analysis revealed that the data points were poorly described by a straight line and therefore that the use of linear slope to characterize the amplitude-intensity relationship is unwarranted.

Blinking↗
PubMedDate not supplied

Pinhole cameras: artifacts modifications, and recording of pinhole images of screen-film systems.

This paper will discuss three points concerning the x-ray pinhole camera: a) pinhole artifacts, which may erroneously be interpreted as off focus radiation, will be described along with a simple method of eliminating these artifacts, b) modifications to a commercially available pinhole camera which simplifies its use and allows for the proper leveling of the pinhole mounting plate will be presented, and c) the use of screen-film cassettes to reduce the required technique for recording the pinhole image will be discussed along with data indicating the expected error with this technique relative to dental film recording.

Radiography↗
PubMed1981

Prescreening of cervical smears using two-parameter flow cytometry. Cytologic identification of artifacts.

Individual properties of gynecologic specimens can produce artifacts in flow cytometric (FMC) measurements, possibly leading to false interpretations. An identification of such artifacts was undertaken by parallel FCM and microscopic investigations. One hundred fifty unselected cervical smears were measured by FCM using the fluorochromes 4'-6-diamidino-2-phenylindole (DAPI) for DNA and sulforhodamine (SR 101) for protein. Microscopic specimens were stained by the Papanicolaou technique, and a detailed cytogram was prepared from each smear. FCM discrimination of fluorochrome-stained superficial and intermediate cells was very difficult. On the other hand, a correlation could be established between the fraction of cells from the deeper epithelial layers in the microscopic cytogram and the mean protein content in the FCM histogram. Furthermore, the role of microorganism could be elucidated. Some microorganisms may produce a reduction of the protein content by cytolytic changes. Other microorganisms adhere to the cell surface, resulting in a misleading increase of the DNA fluorescence. Implications for the problem of false alarms are discussed.

Bacteria↗
PubMed1980

Theoretical studies of image artifacts and counting losses for different photon fluence rates and pulse-height distributions in single-crystal NaI(T1) scintillation cameras.

Using computer simulations, we have developed a theoretical model to explain the correlation between counting losses and image artifacts in single-crystal NaI(T1) scintillation cameras. The theory, valid for scintillation cameras of the Anger type, is based on the physical properties of the NaI(T1) crystal. Based on a statistical model using random numbers, pulse trains of the light pulses from scintillations were simulated. Pulse-height distributions for different event rates were calculated, with various Compton distributions. Images of point sources and line sources were generated. Counting losses and image artifacts were dependent on the shape of the pulse-height distribution. The calculated counting losses decreased with larger Compton distributions, due to increasing numbers of pileup events in the energy window; this also caused severe image distortion. The improvement of the spatial resolution with pileup rejection was demonstrated. The theoretical results are in good agreement with experimental results obtained previously. It is concluded that, in modern cameras, the decay time of the scintillation determines the amount of pileup, and the resolving time of the electronics governs the count rates. The results indicate that in some modern cameras the limits of the count-rate capacity in Anger cameras may be reached.

Elementary Particles↗
PubMed1980

[Atrial dissociation simulated by respiratory artifacts. Case report].

A case of likewise atrial dissociation in a twelve years old patient affected by mucovisclosis with severe respiratory failure is described. The classic criteria of the atrial dissociation were met in the ECG, in which, beside the sinus P waves, low P-like waves, whose rate was 69/m', were present: they did not conduct to the ventricles and were independent from the sinus rhythm. Such waves always coincided with the beginning of the inspiration, and disappeared during the apnoea. So they were not believed as being the results of electrical forces of the heart, but artifacts produced by respiratory movements. The diagnostic criteria of the atrial dissociation are discussed on the basis of these observations. the exclusion of artifacts, especially the respiratory ones, and the demonstration, obtained through the intracavitary ECG, that the waves are really produced by the heart, are necessary to diagnoses the arrhythmia. By the application of these diagnostic criteria only one of the cases found in the Literature has been accepted as demonstrative of atrial dissociation due to complete intraatrial block in man.

Child↗
PubMed1994

Potential diagnostic pitfalls caused by blood film artifacts in prolymphocytic leukaemia. Observations in two cases.

The diagnosis of lymphoproliferative disorders is based on a combined evaluation of the clinical, immunological and morphological findings. Cytological details may vary with the quality of the smear. We report two cases of prolymphocytic leukaemia in which cytoplasmic hairs or protrusions were observed when the films were not dried quickly. In one case the artifacts led to an initial erroneous interpretation of hairy cell leukaemia 'variant'. The cytoplasmic outline was smooth in both cases when the smears were immediately fan-dried. The findings underscore the necessity of high standards of excellence, even for the simple technique of blood film preparation, in order to avoid undesirable artifacts which may result in diagnostic misinterpretation.

Aged↗
PubMed1976

Artifacts produced during acid-catalyzed methanolysis of sterol esters.

Sterol esters were transesterified within 1 hr using either acid or base catalysts. Acid-catalyzed methanolysis of sterol esters with HCl, H2SO4, or BF3 leads to the formation of two artifacts derived from the sterol portion of the molecule; they were identified as dehydrated and methoxylated derivatives of sterols. These two artifacts were not produced using a base-catalyzed methanolysis with NaOCH3.

Chemical Phenomena↗
PubMed1999

Mass spectrometric analysis of Klebsiella pneumoniae ssp. pneumoniae rough strain R20 (O1-: K20-) lipopolysaccharide preparations: identification of novel core oligosaccharide components and three 3-deoxy-D-manno-oct-2-ulopyranosonic artifacts.

In an attempt to find the best approach for the mass spectrometric analysis of the whole range of lipopolysaccharide (LPS) structures from Klebsiella pneumoniae ssp. pneumoniae rough strain R20 (O1-:K20-), various methods of LPS preparation were applied and the products were analyzed using a range of mass spectrometric techniques. The most productive approach proved to be the removal of lipid A by mild acid hydrolysis and the study of the core oligosaccharide structures using nanoelectrospray time-of-flight mass spectrometry (TOF-MS) in combination with collision-induced dissociation tandem mass spectrometry. This procedure is very sensitive, but results in the generation of a reducing 3-deoxy-D-manno-oct-2-ulopyranosonic acid residue (Kdo) that is susceptible to the formation of artifacts, which give rise to pseudomolecular ions 18, 46, and 88 Da below the pseudomolecular ion for the unmodified species. Alternatively, matrix-assisted laser desorption/ionization TOF-MS combined with post-source decay can be used to study the de-O-acylated LPS preparation and especially to identify those residues bearing phosphate groups and the residues involved in the linkage between the core and lipid A. In addition to the five LPS core structures defined using NMR spectroscopy by Süsskind et al., several extra related LPS structure were identified. Larger LPS species were observed, which surprisingly do not represent species containing longer versions of the novel Klebsiella heptoglycan, but instead are species having the defined core and heptoglycan extended with up to three extra hexuronic acid and one or two extra hexose residues.

Acylation↗
PubMed2000

Identification of an artifact in the mass spectrometry of proteins derivatized with iodoacetamide.

Derivatization of cysteinyl residues is often used to prevent the formation of disulfide bonds during protein isolation and analysis. The most commonly used reagents are iodoacetic acid and iodoacetamide, which increase the molecular mass of the protein by 58 or 57 Da, respectively, for each derivatized cysteine. A possible side reaction is derivatization of methionine. In our analysis of derivatized human lens alphaA-crystallins, we found an apparent molecular mass 48 Da lower than the mass expected for alphaA-crystallin with the cysteines carboxyamidomethylated. Analysis of a tryptic digest of this protein showed that both cysteines and one methionine had been derivatized. Peaks indicating a molecular mass 48 Da less than expected for the protein with only cysteines derivatized were attributed to fragmentation of the derivatized methionine through collision-induced dissociation in the electrospray ionization source. An awareness of this artifact is important to investigators searching for proteins and their modified forms in complex mixtures.

Aged↗