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At least 1,333 records · Page 74Linked to original sources
PubMed1978

An artifact produced by boiling adenyl cyclase reaction mixtures prior to the cyclic AMP-radioimmunoassay.

An artifact of procedure has been detected in the adaptation of the cAMP-radioimmunoassay to the analysis of adenyl cyclase activity. When reaction mixtures containing ATP and MgCl2 were boiled to terminate the enzyme assay, a cAMP-like decrease in antigen-binding was found. This decrease was dependent upon the presence of ATP, was linear to at least 5 min of boiling time, and could be destroyed with the addition of commercial phosphodiesterase. As significant levels of the nonenzymatically formed product resulted only when samples were boiled, alternative methods of terminating cyclase reactions are suggested.

Adenosine Triphosphate↗
PubMed1993

2,3,4-Tri-O-acetyl-1,6-anhydro-beta-D-mannopyranose, an artifact produced during carbohydrate analysis. A total synthesis of 2,3,5-tri-O-acetyl-1,6-anhydro-beta-D-mannofuranose.

This study confirms that 2,3,4-tri-O-acetyl-1,6-anhydro-beta-D-mannopyranose is an artifact produced during carbohydrate analysis. A new synthesis of 2,3,5-tri-O-acetyl-1,6-anhydro-beta-D-mannofuranose is also described, and a novel dimer, 1,6':6,1'-dianhydro-2,3:2',3'-di-O-isopropylidene-5,5'-di-O-(1-methox yethyl)-di - alpha-D-mannofuranose, has been isolated. The structure of the dimer is confirmed by X-ray analysis of a derivative, 1,6':6,1'-dianhydro-2,3:2',3'-di-O-isopropylidene-di-alpha-D-mannofur anose.

Artifacts↗
PubMed1993

Minor recorder imperfections can cause artifacts in the RR interval spectrum derived from Holter recordings.

Spectral analysis of the heartbeat (RR) interval is a powerful tool for noninvasively assessing the autonomic nervous system. In addition, it may prove to be valuable in stratifying patients at risk for cardiac death. The authors report on a case in which spectral analysis of the RR interval exhibited harmonically related peaks within the physiological range that defied physiological explanation. Analysis showed that these peaks resulted from a subtle abnormality of the Holter recorder that was not apparent in the observed electrocardiogram. Since this type of abnormality can be produced by either minor damage or a manufacturing error in any brand of Holter recorder, the RR interval spectrum derived form a Holter electrocardiogram should always be critically examined for this particular artifact.

Artifacts↗
PubMed1992

Taming cut-off induced artifacts in molecular dynamics studies of solvated polypeptides. The reaction field method.

In this paper we present a model system of a solvated polypeptide, which is a suitable reference platform for the systematic exploration of methods for taming artifacts introduced by an incorrect treatment of long-range Coulomb forces. The essential feature of the system composed of an alpha-helical peptide and 1021 water molecules is the strict neutrality of all charge groups. The dynamical properties of the peptide, i.e. unfolding or maintenance of the helix, already give first hints on the influence of boundary effects. A rigorous and deeper insight is gained, however, if analyzing the system by means of the generalized Kirkwood g-factor, which projects the net dipole moment of concentric spheres onto the respective dipole moment of the reference charge group. The g-factor is a global measure for, and a sensitive probe of, the orientational structure, which in its turn reflects even the smallest inconsistencies in the treatment of long-range forces. While the cut-off scheme failed the g-factor test, the "reaction field" method, the simplest cut-off correction scheme, enables a consistent description. In other words, with the aid of the reaction field, the correct orientational structure is restored. As a consequence, the helix stability is regained and we were able to calculate the dielectric constant epsilon approximately 55 to 60 for our system, which is slightly below the corresponding value epsilon SPC = 66 of the pure solvent.

Amino Acid Sequence↗
PubMed1992

The low affinity binding site for the cocaine analog, WIN 35,428 is an artifact of freezing caudate tissue.

Binding of the cocaine analog [3H] WIN 35,428 was investigated in rat and rabbit caudate. In membranes prepared from fresh tissue, [3H] WIN 35,428 binding was characterized by a single high affinity site with a Kd of 2.5 nM for the rabbit and 5.3 nM for the rat. In contrast, [3H] WIN 35,428 binding to membranes prepared from frozen tissue (stored at -70 degrees C) revealed two binding sites, a high affinity site similar to the one observed in membranes from fresh tissue and a low affinity site with a Kd of 39 nM for the rabbit and 65 nM for the rat. The low affinity WIN 35,428 binding site was observed only in membranes derived from frozen tissue, suggesting that it was an artifact produced by the freezing/thawing process.

Animals↗
PubMed1992

Ion channels. Preventing artifacts and reducing errors in single-channel analysis.

The power of single-channel analysis techniques has rapidly expanded during the past few years, giving investigators increased ability to identify models and estimate parameters while reducing error and artifacts. At present, however, there is no single best method, as even the most advanced techniques have various limitations which depend on the experimental data and models being examined. Consequently, for the examined models and experimental data, the most critical part of single-channel analysis is to estimate errors and evaluate the ability of the methods used to discriminate among possible gating mechanisms. The magnitudes of the errors and the ability to identify models and estimate parameters depend on the models being examined as well as the experimental conditions and data. Consequently, the evaluation of the errors associated with each method needs to be repeated when the experimental data and examined models change.

Artifacts↗
PubMed1994

Artifact-free application of drugs into the avian endolymphatic space.

A push-pull system is described that allows artifact-free application of drugs into very small volumes such as, e.g., the endolymphatic space of the inner ear. The system consists of two syringes, the pistons of which are fixed together and driven by an Oriel motordrive. The syringes are connected to the pipette holders and microcapillaries by PVC tubes. One capillary is used to expel a certain volume, whilst the other one aspirates the same volume. A balanced exchange of fluids within a given space without an overall change in volume is therefore possible.

Action Potentials↗
PubMed1993

Artifact reduction in magnetic stimulation.

A new biopotential amplifier is described in which the stimulus artifact from recordings of electrically or magnetically evoked biopotentials is minimized by a special active filter. The amplifier is tested in different experiments and the recordings are compared to standard EMG recordings.

Action Potentials↗
PubMedDate not supplied

Microbial cell-wall contaminants in peptides: a potential source of physiological artifacts.

Microbial cell-wall products (MCWP) such as endotoxins are easily introduced into peptides produced under standard laboratory conditions. Because these products stimulate the induction of cytokines and other mediators, which, in turn, trigger a broad range of physiological responses. MCWP in peptide preparations are potential sources of artifacts. This brief tutorial outlines the physical/chemical nature of MCWP, some of their sources, their physiological effects, and a simple method to control for them in some peptide preparations.

Artifacts↗
PubMed1992

Artifact formation during gas chromatographic-mass spectrometric analysis of a methylsulfinyl-containing metabolite.

During gas chromatographic-mass spectrometric analysis using a heated injector, 1-methylthio-4-methylsulfinyltetrachlorobenzene degraded to form tetrachlorothioanisole. Similar reductive defunctionalizations have been reported during in vivo metabolisms. Caution should be used to distinguish metabolites from artifacts which may be formed during the analysis of methylsulfoxides.

Artifacts↗
PubMed1992

Motion artifact suppression: a review of post-processing techniques.

Patient motion during data acquisition in magnetic resonance imaging causes artifacts in the reconstructed image, which for two-dimensional Fourier transform imaging techniques appear as blurring and ghost repetitions of the moving structures. While the problem with intra-view effects has been effectively addressed using gradient moment nulling techniques, there is no corresponding technique for inter-view effects with equal effectiveness and general applicability. A number of techniques have been proposed for correcting the inter-view effects, and these may be divided into those that minimise the corruption of the data, and those that post-process the data to restore the image. The techniques in the former category are briefly reviewed, then those in the latter category are examined in detail. These are analysed in terms of motion model, model parameter estimation, and data correction.

Artifacts↗
PubMed1994

Simulation of susceptibility artifacts in 2D and 3D Fourier transform spin-echo and gradient-echo magnetic resonance imaging.

A method is presented for simulating susceptibility artifacts in 2D and 3D spin-echo and gradient-echo imaging of arbitrary susceptibility distributions. The method incorporates object induced field perturbations in the time domain (k-space) and is demonstrated for spherical nonuniformities in susceptibility. Both simulations and experimental results for multi-slice 2D and 3D imaging of phantoms and human subjects are provided.

Artifacts↗
PubMed1994

Chemical shift misregistration artifact: increased conspicuity following intravenous administration of gadopentetate dimeglumine.

We have observed increased conspicuity of chemical shift misregistration artifact (CSMA) associated with enhancing structures on MR images after the intravenous administration of gadopentetate dimeglumine compared with corresponding unenhanced images. In this study, we investigate the influence of gadopentetate dimeglumine administration on the conspicuity of CSMA in MR imaging of the kidneys. Nine gadopentetate-enhanced and unenhanced T1-weighted images of the kidneys were evaluated in a side-by-side fashion for the conspicuity of both the high and low signal intensity (SI) components of CSMA. A phantom study of saline in a bath of oil and increasing concentrations of gadopentetate dimeglumine in a bath of oil was performed. There was increased conspicuity of both the high and low SI components of CSMA in gadopentetate-enhanced images compared with unenhanced images in all study cases and in the phantom samples containing gadopentetate compared with the saline control. In conclusion, the administration of gadopentetate dimeglumine results in increased conspicuity of CSMA on MR images of the kidneys.

Aged↗
PubMedDate not supplied

Cerebrospinal fluid flow artifact. A possible pitfall on fast-spin-echo MR imaging of the spine simulating intradural pathology.

We have noted that fast-spin-echo T2-weighted images of the cervical and thoracic regions of the spine can produce low-signal artifacts in the spinal subarachnoid space which might be misinterpreted as tumor or abnormal vascular flow voids. These are possibly related to complex cerebrospinal fluid pulsatile flow and should be recognized as artifactual by the radiologist.

Arteriovenous Malformations↗
PubMedDate not supplied

Electrocardiographic artifact corrected with intravenous nitroglycerin.

A number of conditions can cause ST segment changes exclusive of myocardial ischemia, and nitroglycerin has been administered in such cases. We report a case of artifactual ST depression that was managed with intravenous nitroglycerin. In this case, the cause of the ECG artifact might have been the apical heartbeat.

Artifacts↗
PubMed1996

Methods and reagents. Eliminating banding artifacts from SDS-PAGE.

Methods and reagents is a unique monthly column that highlights current discussions in the newsgroup bionet.molbio.methds-reagnts, available on the Internet. This month's column discusses how to avoid some artifacts when running SDS-polyacrylamide gels, and some other tips for reducing the cost of lab supplies are given as well. For details on how to partake in the newsgroup, see the accompanying box.

Artifacts↗
PubMed2005

Major artifacts encountered in studying biological samples containing ferric protoporphyrin IX.

Heme (ferric protoporphyrin IX, FP) dissolves very rapidly into the lipid phase of membranes, and a large number of studies have focused attention on its possible toxic effect in whole cells or isolated membranes. However, because of its molecular structure and reactivity, different problems can be encountered during the course of studying biological samples containing FP. In this article, we discuss important interferences by FP and artifacts that can affect the experimental values. First, FP interferes with the Lowry's protein determination; therefore, membranes containing FP are overestimated in their protein content determined by this procedure. Second, freezing membranes at -20 degrees C artifactually increases the local concentration of FP, thereby enhancing FP-induced lipid peroxidation. Third, in the presence of thiol compounds such as N-acetyl cysteine, FP is degraded to products that interfere with the thiobarbituric acid assay, one of the most widely used methods to measure the extent of lipoperoxidation.

Acetylcysteine↗
PubMed2004

Optimization of an independent component analysis approach for artifact identification and removal in magnetoencephalographic signals.

OBJECTIVE: To propose a noise reduction procedure for magnetoencephalography (MEG) signals introducing an automatic detection system of artifactual components (ICs) separated by an independent component analysis (ICA) algorithm, and a control cycle on reconstructed cleaned data to recovery part of non-artifactual signals possibly lost by the blind mechanism. METHODS: The procedure consisted of three main steps: (1) ICA for blind source separation (BSS); (2) automatic detection method of artifactual components, based on statistical and spectral ICs characteristics; (3) control cycle on 'discrepancy,' i.e. on the difference between original data and those reconstructed using only ICs automatically retained. Simulated data were generated as representative mixtures of some common brain frequencies, a source of internal Gaussian noise, power line interference, and two real artifacts (electrocardiogram=ECG, electrooculogram=EOG), with the adjunction of a matrix of Gaussian external noise. Three real data samples were chosen as representative of spontaneous noisy MEG data. RESULTS: In simulated data the proposed set of markers selected three components corresponding to ECG, EOG and the Gaussian internal noise; in real-data examples, the automatic detection system showed a satisfactory performance in detecting artifactual ICs. 'Discrepancy' control cycle was redundant in simulated data, as expected, but it was a significant amelioration in two of the three real-data cases. CONCLUSIONS: The proposed automatic detection approach represents a suitable strengthening and simplification of pre-processing data analyses. The proposed 'discrepancy' evaluation, after automatic pruning, seems to be a suitable way to render negligible the risk of loose non-artifactual activity when applying BSS methods to real data. SIGNIFICANCE: The present noise reduction procedure, including ICA separation phase, automatic artifactual ICs selection and 'discrepancy' control cycle, showed good performances both on simulated and real MEG data. Moreover, application to real signals suggests the procedure to be able to separate different cerebral activity sources, even if characterized by very similar frequency contents.

Algorithms↗