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PubMed1989

Correction of ocular artifacts in EEGs using an autoregressive model to describe the EEG; a pilot study.

The basic idea in eye movement (EM) artifact corrections is that the actual recording is the summation of brain potentials (true EEG) and artifact. Often a regression analysis is performed, using simultaneous EEG and EOG data, to find the parameters describing the relationship between artifact and EOG derivations (EOGs). Our method uses a maximum likelihood parameter estimation and considers data from preceding sample moments as well, since there may be a delay in the artifact transferring over the scalp. For the error term (true EEG) an autoregressive function is used. Results from estimations on data from one volunteer indicate that a delay need not be considered and that 3 autoregressive parameters are sufficient. For F3 4 EOGs give only somewhat better results than 2 EOGs. For C3 and C4 2 EOGs are sufficient. For practical reasons for each of these 3 EEG recordings, 2 EOGs were used to perform corrections. Corrections were performed using either the parameters estimated for EMs and blinks together, or the parameters estimated for EMs only (used for EMs), or the parameters estimated for blinks only (used for blinks). For EMs the differences between these corrections are very small. For blinks the differences are much larger. Parameters estimated for one trial may be used to correct other trials, recorded within a period of about 15 min preceding or following that trial.

Blinking↗

PubMed1990

A digital technique for stimulus artifact reduction.

A method of recovering compound muscle action potentials which are overwhelm by a stimulus artifact is presented. In the specific example reported, such action potentials were recorded from the hamster diaphragm using an apposing platinum electrode for both stimulation and recording. To recover the artifact-free action potential, a combination of digital data acquisition and simple signal processing was employed. The recording of a stimulus artifact from a sub-threshold stimulus was used to subtract the artifact component from subsequent recordings and thus faithfully reveal the action potentials. The technique should find application in other preparations.

Action Potentials↗

PubMed1990

Effect of scan format on refraction artifacts.

Refraction artifacts occur when the ultrasound beam is bent from its original direction as it passes through a boundary between tissues having different sound speeds. Refraction artifacts result in both the improper positioning and the improper brightness of echoes displayed in clinical sonograms. The effect of scan format on the sonographic appearance of several refraction artifacts due to a circular object possessing a sonic speed differing from its surrounding tissue was studied using a mathematical model and computer generated images. A quantitative index of artifact prominence was developed to compare the differences between the rectilinear and the sector scan formats. Theoretically predicted results were compared with actual sonograms of a specially designed phantom. Results included the finding that the retrolenticular afterglow was more prominent in the sector scan format, and that differences were most prominent when the refracting object was close to the transducer.

Animals↗

PubMedDate not supplied

Multiple spin-echo MR imaging of the body: image contrast and motion-induced artifact.

For a given TR and TE, image quality changes when the number of spin echoes obtained is varied. To investigate the importance of this in clinical imaging, a total of 4 patients and 9 volunteers had MRI examinations of the abdomen (n = 7) and/or pelvis (n = 8) which included at least 2 sequences with identical TR (2000 or 2500 ms), TE (80 ms) and other parameters, but with a different series of refocusing pulses. Sequences included single-echo (S), asymmetric and symmetric double-echo (AD and SD) and quadruple-echo (Q) techniques. Image contrast and severity of motion-induced artifact was measured via blind examination by 3 independent MRI radiologists and calculation of signal-difference, signal-difference-to-noise ratios and intensity of motion-induced "ghost artifact." The order of decreasing signal differences was S, SD, AD and Q, and all of three liver lesions were better seen with S than with SD techniques. These observations are consistent with signal loss from cumulative inaccuracies from multiple 180 degrees RF pulses. The order of increasing intensity of ghost artifact was Q, SD, AD and S, consistent with the beneficial motion artifact-reducing effects of even-echo rephasing. Knowledge of these effects of multi-echo imaging allows one to make informed decisions about imaging protocols rather than to simply obtain multiple echoes "because they are free."

Abdomen↗

PubMed1990

CSF flow artifact reduction using cardiac cycle ordered phase-encoding method.

The flow effects appear as a change of phase as well as signal intensity in NMR imaging. Since the flow of blood and CSF (cerebrospinal fluid) is pulsatile due to the heart pumping, their velocities are not constant during NMR imaging. This type of velocity fluctuation such as the blood or CSF flow induces irregular flow-dependent phase shifts, which have been one of the main causes of flow artifacts in NMR imaging. In order to reduce the flow artifacts, especially the CSF flow artifacts, a new cardiac cycle ordered phase encoding method is proposed and has been studied. This proposed technique utilizes the cardiac cycle as a precursor for the phase encoding gradients similar to the ROPE (respiratory ordered phase encoding) technique which has been used for respiratory motion artifact reduction. The basic concept and its applications are discussed together with the experimental results obtained with human volunteers using the KAIS 2.0 2.0 T whole-body NMR imaging system.

Brain↗

PubMed2005

Preschoolers favor the creator's label when reasoning about an artifact's function.

The creator of an artifact, by virtue of having made the object, has privileged knowledge about its intended function. Do children recognize that the label an artifact's creator uses can convey this privileged information? 3- and 4-year-olds were presented with an object that looked like a member of one familiar artifact category, but which the speaker referred to with the label of a different familiar category (e.g. a key-like object was called a "spoon"). Children who heard the speaker refer to the object as something she made were more likely to assign its function on the basis of the anomalous label she used than those who heard it referred to as something the speaker found. Thus, even very young children expect a unique connection between the label the creator of an artifact uses and the function she intends it to have.

Attitude↗

PubMed2006

Reasoning about artifacts at 24 months: the developing teleo-functional stance.

From the age of 2.5, children use social information to rapidly form enduring function-based artifact categories. The present study asked whether even younger children likewise constrain their use of objects according to teleo-functional beliefs that artifacts are "for" particular purposes, or whether they use objects as means to any desired end. Twenty-four-month-old toddlers learned about two novel tools that were physically equivalent but perceptually distinct; one tool was assigned implicit function information through a short demonstration. At test, toddlers returned to the demonstrated tool when asked to repeat the task, but, unlike older children, also used it for another task. Results imply that at 24 months, toddlers expect artifacts to have functions and proficiently use a model's intentional use to inform tool choices, suggesting cognition that differs from that of tool-using monkeys. However, their artifact representations are not yet specified enough to support exclusive patterns of tool use.

Child, Preschool↗

PubMed2006

Artifacts in the GC-MS profiling of underivatized methamphetamine hydrochloride.

When underivatized methamphetamine hydrochloride (MA.HCl) in methanol is subjected to the instant gas chromatographic-mass spectrometric (GC-MS) profiling with old inlet liners at temperatures above 200 degrees C, appreciable amounts of N,N-dimethylamphetamine (DMA) and amphetamine (AP) are produced. The presence of these two artifacts is attributed to the N-demethylation and N-methylation reactions of MA as well as methyl group exchange with methanol. These artifacts are only produced in old injection port liners and at elevated temperatures. The formation of artifacts is proportional to concentration of MA.HCl. It is suggested that special cautions and measures be undertaken to prevent artifacts.

Journal Article↗

PubMed2005

Missing first points and phase artifact mutually entangled in FT NMR data--noniterative solution.

Even moderate distortion at the beginning of the NMR signal contributes significantly to the baseline in the reciprocal domain, when the FID-type experiment is considered. If constant phase artifact is also involved, the net problem cannot be resolved accurately, according to its constituents considered in separation. This issue is particularly severe for powder patterns in solids, featuring complex broadband spectra, which substantially mask the baseline behavior. The complete correction procedure should intrinsically deal with both artifacts, due to the mutual dependency. The aim of this work is to indicate the possibility for the exact treatment of baseline and constant phase artifacts together, providing precise measure whether the correction is successful. We have found the analytical, noniterative solution for this coupled problem in the closed form. In this paper, we introduce the correction efficiency concept in order to have the measure for the correction reliability of the resulting spectrum. Relevant efficiency parameter eta is the subject for quantitative analysis resulting in certain constraints for the measurement. We have determined exemplar trends for this parameter as a function of experimental variables such as signal-to-noise ratio and missing points number. The method is model-free and drawn from the origin of the baseline artifact; therefore has potential to work for a broad range of applications.

Journal Article↗

PubMed2002

Focal volume optics and experimental artifacts in confocal fluorescence correlation spectroscopy.

Fluorescence correlation spectroscopy (FCS) can provide a wealth of information about biological and chemical systems on a broad range of time scales (<1 micros to >1 s). Numerical modeling of the FCS observation volume combined with measurements has revealed, however, that the standard assumption of a three-dimensional Gaussian FCS observation volume is not a valid approximation under many common measurement conditions. As a result, the FCS autocorrelation will contain significant, systematic artifacts that are most severe with confocal optics when using a large detector aperture and aperture-limited illumination. These optical artifacts manifest themselves in the fluorescence correlation as an apparent additional exponential component or diffusing species with significant (>30%) amplitude that can imply extraneous kinetics, shift the measured diffusion time by as much as approximately 80%, and cause the axial ratio to diverge. Artifacts can be minimized or virtually eliminated by using a small confocal detector aperture, underfilled objective back-aperture, or two-photon excitation. However, using a detector aperture that is smaller or larger than the optimal value (approximately 4.5 optical units) greatly reduces both the count rate per molecule and the signal-to-noise ratio. Thus, there is a tradeoff between optimizing signal-to-noise and reducing experimental artifacts in one-photon FCS.

Biophysical Phenomena↗

PubMed2001

Developmental changes within the core of artifact concepts.

Three experiments addressed the relative importance of original function and current function in artifact categorization. Subjects were asked to judge whether an artifact that was made for one purpose (e.g. making tea) and was currently being used for another purpose (e.g. watering flowers) was a teapot or a watering can. Experiment 1 replicated the finding by Hall (1995) (unpublished manuscript) that adults rely on the original function of an artifact over a current function in their kind judgments. Experiments 2 and 3 revealed that whereas the kind judgments of 6-year-olds, like those of adults, patterned with the original function, those of 4-year-olds did not. Four-year-olds were influenced by the order in which the functions were mentioned in the story. Further, in their justifications 6-year-olds and adults referred to the origin of the objects, whereas 4-year-olds virtually never did. We conclude that 6-year-olds have begun to organize their understanding of artifacts around the notion of original function, and that 4-year-olds have not. The data are discussed as they bear on children's understanding of the design stance (Dennett, D. C. (1987).

Adult↗

PubMed2004

The role of historical intuitions in children's and adults' naming of artifacts.

It is commonly assumed that artifacts are named solely on the basis of properties they currently possess; in particular, their appearance and function. The experiments presented here explore the alternative proposal that the history of an artifact plays some role in how it is named. In three experiments, children between the ages of 4 and 9 years and adults were presented with familiar artifacts whose appearance and function were then radically altered. Participants were tested as to whether they believed that the modified objects were still members of the artifact kind. Results indicate that object history becomes increasingly important over the course of development.

Adult↗

PubMed1987

Analysis of acetone-hexane artifacts produced in the Soxhlet extraction of solid environmental samples.

A study was performed to examine the artifact formation during the acetone-hexane Soxhlet extraction of suspended materials collected on glass fiber filters. Capillary gas chromatographic analysis showed a great number of artifacts of significant concentration in the Soxhlet extractions of the filters after cleaning, the acetone solvent blank and the acetone-hexane Soxhlet blank. Gas chromatographic-mass spectrometric analysis indicated that the compounds are primarily condensation products of acetone produced during the Soxhlet extraction process and solvent impurities. Acetone and hexane washes of the glass fiber filters showed a large variety of compounds to be present on the filters as received from the manufacturer. A reaction scheme is proposed to explain the formation of some of the acetone condensation products identified in this study. A comparison study using methylene chloride to clean and extract the filters showed considerably less artifact formation and solvent impurities. The development of an appropriate quality assured extraction method, which minimizes artifact formation, is needed for the broad spectrum analysis of non-polar trace organics associated with suspended materials in aquatic samples.

Acetone↗

PubMed1999

Artifacts in trimethylsilyl derivatization reactions and ways to avoid them.

Trimethylsilyl derivatives are routinely employed in gas chromatography to increase the volatility and stability of organic compounds containing active hydrogens. Normally only the desired derivative is formed when organic compounds are derivatized with common silylation reagents. However, some compounds form additional unexpected derivatives or by-products (artifacts). Artifact formation leads to multiple peaks for the same compound or unexpected components in the gas chromatographic analysis of mixtures. This review includes silylation artifacts identified in our laboratory by mass spectrometry during the last 20 years and references to those found in the literature. Also, means of avoiding artifact formation are discussed in detail.

Aldehydes↗

PubMed1979

Unusual artifacts in electrocardiographic monitoring.

Three unusual artifacts noted during Holter and telemetry monitoring, not previously described, are presented. Recognition of the artifacts prevented misinterpretation and wrong treatment. The clues to the identification of the artifacts and the need for avoiding wrong interpretation and inappropriate treatment are discussed. The cause of the telemetry artifact is discussed.

Adult↗

PubMed2000

1. Positron Emission Tomography of Thoracic Malignancies. Reduction of Myocardial Fluorodeoxyglucose Uptake Artifacts With a Carbohydrate Restricted Diet.

Purpose: To reduce the artifact caused by cardiac uptake of F-18 fluorodeoxyglucose (FDG); we investigated the change in myocardial FDG uptake after placing a group of patients on a carbohydrate-restricted diet.Methods: Case control study involving 130 whole body FDG PET scans. 73 scans were of patients on carbohydrate-restriction; the remaining 57 were without dietary restrictions. Dietary intake for the last meal prior to scanning was recorded for both groups. Coronal and axial images were assessed and scored based on myocardial FDG uptake the presence of associated image artifacts.Results: Of the 73 patients on the diet, 50 did not consume carbohydrates, while of the 57 patients without dietary restriction, 13 did not consume carbohydrates. Of the 67 patients from both groups who consumed carbohydrates prior to their PET scan, 17 (25.4%) had a clinically significant image artifact versus only 6 (9.5%) of the 63 patients who did not consume carbohydrates (P = 0.018) in their meals prior to scanning. The odds ratio was calculated to be 3.23 (confidence interval 1.09-10.00), indicating that the risk a clinically significant image artifact will occur is 3.23 times higher for patients who consume carbohydrates in their last meal prior to scanning.Conclusion: A substantial reduction in the prevalence of myocardial FDG uptake image artifacts among patients who did not consume carbohydrates was observed. A carbohydrate dietary restriction prior to scanning may play a significant role in increasing lesion detectability and in preventing false negative scans when imaging for thoracic neoplasm.

Journal Article↗

PubMed2002

Reduction of myocardial 2-deoxy-2-[18F]fluoro-D-glucose uptake artifacts in positron emission tomography using dietary carbohydrate restriction.

PURPOSE: The use of carbohydrate restriction prior to 2-deoxy-2-[18F] positron emission tomography (FDG-PET) to reduce image artifacts caused by myocardial FDG uptake was investigated. PROCEDURES: Ninety-six whole-body FDG-PET scans were studied. Dietary intake of the meal prior to scanning was recorded. Coronal and transverse images were assessed visually and scored based on myocardial FDG uptake and the presence of associated image artifacts. RESULTS: Of 49 patients who consumed carbohydrates prior to PET, 14 (28.6%) had a clinically significant image artifact versus only five (10.6%) of 47 patients who did not consume carbohydrates (P = 0.0275). A 3.36 times increased risk (confidence interval 1.00-12.97) for clinically significant image artifacts was calculated for patients who consume carbohydrates in their last meal prior to scanning. CONCLUSIONS: With the rising use of FDG-PET in the evaluation of intra-thoracic malignancies, dietary carbohydrate restriction prior to scanning may play a role in increasing lesion detectability and reducing false negative scans.

Journal Article↗

PubMed1984

[Multiple image artifacts with linear sonic transducers].

The multielement arrays used nowadays for diagnostic purposes can, by means of digital signal processing, produce exact images with no problem. When physical limits were reached however, geometric image artifacts also became more evident, thereby making diagnosis more difficult or uncertain. Multiple images became especially evident during tests in the early stages of pregnancy, making it harder to differentiate between single and multiple pregnancies , particularly as dynamic processes such as the heart beat can be shown double at a certain phase in the pregnancy. Artifacts were also observed in the form of multiple echos during control checks on the position of intrauterine contraceptive devices and when investigating gynaecological tumors. These artifacts are ascribed to sonic behaviour at interfaces and are representable as a function of the sonic angle of incidence primarily in one plane--the cross section. They appear virtually symmetrical and can be wiped out by moving the sonic transducer. Although there is no problem in recognising the double phenomena as being artifacts in checks on the position of IUD's, all multiple structures should be clarified by suitable examination techniques especially during the early stages of pregnancy and with tumours.

Diagnosis, Differential↗