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At least 1,171 records · Page 65Linked to original sources
PubMed2000

Mathematical Modeling and Numerical Simulation of Magnetic Susceptibility Artifacts in Magnetic Resonance Imaging.

The technique used to recognise information in Magnetic Resonance Imaging (MRI) is based on electromagnetic fields. A linearly varying field (around 10(-2) Tesla per meter) is added to a strong homogeneous magnetic field (order of magnitude of approximately one Tesla). When these fields are disturbed by the presence of a paramagnetic material, in the sample for instance, the resulting image is usually distorted, these distortions being termed artifacts. Our goal is to present a method, assuming the field disturbances are known, to construct the resulting images. A mathematical model of the MRI process is developed. The way the images are distorted in intensity and shape is explained and an algorithm to simulate magnetic susceptibility artifacts is deduced.

Journal Article↗
PubMed1990

Schizophrenic birth seasonality and the age-incidence artifact.

Lewis (1989) dismisses a large number of articles in which schizophrenic winter birthrate excesses have been reported as the result of either design problems or the age-incidence artifact. We review about 20 studies in which the effects of age incidence have been controlled in one way or another. The majority support the conclusion that the seasonality effect is due neither to artifact nor deficient research design. We also correct two significant errors in Lewis' description of our prior work.

Adult↗
PubMed2001

GHB. Club drug or confusing artifact?

GHB can be produced either as a pre- or postmortem artifact. The authors describe two cases in which GHB was detected and discuss the problem of determining the role of GHB in each case. In both cases, NaF-preserved blood and urine were analyzed using gas chromatography. The first decedent, a known methamphetamine abuser, had GHB concentrations similar to those observed with subanesthetic doses (femoral blood, 159 microg/ml; urine, 1100 microg/ml). Myocardial fibrosis, in the pattern associated with stimulant abuse, was also evident. The second decedent had a normal heart but higher concentrations of GHB (femoral blood, 1.4 mg/ml; right heart, 1.1 mg/ml; urine, 6.0 mg/ml). Blood cocaine and MDMA levels were 420 and 730 ng/ml, respectively. Both decedents had been drinking and were in a postabsorptive state, with blood to vitreous ratios of less than 0.90. If NaF is not used as a preservative, GHB is produced as an artifact. Therefore, the mere demonstration of GHB does not prove causality or even necessarily that GHB was ingested. Blood and urine GHB concentrations in case 1 can be produced by a therapeutic dose of 100 mg, and myocardial fibrosis may have had more to do with the cause of death than GHB. The history in case 2 is consistent with the substantial GHB ingestion, but other drugs, including ethanol, were also detected. Ethanol interferes with GHB metabolism, preventing GHB breakdown, raising blood concentrations, and making respiratory arrest more likely. Combined investigational, autopsy, and toxicology data suggest that GHB was the cause of death in case 2 but not case 1. Given the recent discovery that postmortem GHB production occurs even in stored antemortem blood samples (provided they were preserved with citrate) and the earlier observations that de novo GHB production in urine does not occur, it is unwise to draw any inferences about causality unless (1) blood and urine are both analyzed and found to be elevated; (2) blood is collected in NaF-containing tubes; and (3) a detailed case history is obtained.

Adult↗
PubMed1991

Myocardial imaging artifacts caused by mitral valve annulus calcification.

Knowledge of imaging artifact of myocardial perfusion studies with thallium-201 is critical for improving the diagnostic accuracy of coronary artery disease. Three patients are described who underwent exercise or pharmacologic stress thallium-201 imaging studies and had a moderate, fixed myocardial perfusion defect (scar) involving the posterolateral and inferoposterior walls of the left ventricle. This was an imaging artifact caused by a heavily calcified mitral valve annulus.

Aged↗
PubMed1990

Acoustic prism causing sonographic duplication artifact in the upper abdomen.

A variable prism of fat frequently occurs in the anterior abdominal wall that can produce confusing double-image artifacts on sonograms. This artifact is seen most frequently in the pelvis but is also seen in the upper abdomen, and is related to anatomic variations and the size of some ultrasound transducers. Phantom studies and a review of the CT scans of 100 patients were used to document the anatomy and frequency of occurrence of this variant.

Abdominal Muscles↗
PubMedDate not supplied

Respiration artifacts in MR imaging: reduction by breath holding.

Respiratory motion commonly produces degradation of image quality on magnetic resonance scans of the upper abdomen due to artifacts produced in the direction of the phase encoding gradient. Such artifacts may be reduced, although not eliminated, on image sequences obtained with relatively short acquisition times by means of breath holding during the middle 20% of the sequence.

Diaphragm↗
PubMedDate not supplied

Unusual MR metallic artifact due to steel threads.

Metallic objects are a well known source of artifact in magnetic resonance imaging. We report a case of artifacts created by metallic fibers woven into surgical scrub pants worn by a patient during the examination.

Adolescent↗
PubMed2005

Gestational age discrepancies due to acquisition artifact in the forensic fetal osteology collection at the National Museum of Natural History, Smithsonian Institution, USA.

Previously, numerous techniques have been used to assess either lunar or gestational age from fetal remains, such as from the external dimensions of the fetus, presence or absence of external features and ossification centers. One of the largest fetal collections in the U.S. is assessed with regard to errors in its biologic profile (ancestry, sex and age), the nature of the collection process, the methods of collection and the subsequent considerations for usage. Hrdlicka recorded the age, ancestry, sex and external measurements on card catalogs in the early 1900s for future use. For the purpose of this pilot study, measurements on 38 suitable fetuses stored at NMNH were used to calculate lunar age and compare with the recorded age in the card catalog. The differences between the age assessments are as follows: 20 showed no difference, 11 were discrepant by one month, 6 varied by 2 months and 1 diverged by 5 months. The average difference between lunar ages is 0.74 months, reflecting a nearly three-week difference. The purpose of this paper is to demonstrate that such discrepancies exist and to confirm specimens with accurate ages, which can be marked for future research. Moreover, it is also the purpose of this paper to demonstrate that such bias artifact exists in museum collections, and that this artifact needs to be eliminated from the sample materials prior to study.

Age Determination by Skeleton↗
PubMed1972

Artifacts in the Embedment of Water-soluble Compounds for Light Microscopy.

The relative effectiveness of freeze-drying and freeze-substitution in accurately preserving the distribution of water-soluble compounds in plants tissues was evaluated. Specimens with a known distribution of water-soluble materials (sucrose-infiltrated pith blocks and red beet tissue) were freeze-dried or freeze-substituted and embedded in paraffin, Epon, or methacrylate for microscopic examination. Dried water-soluble compounds were extremely sensitive to only traces of water, which caused severe shrinkage of the vacuolar contents. In spite of care taken to maintain dry conditions, freeze-drying was always accompanied by marked shrinkage of the water-soluble compounds away from the cell walls. Freeze-substitution was successful only if the solvents and embedding media were thoroughly dried and if infiltration was done in a dry box. Other artifacts were also noted, although they were less severe. Artifacts comparable to those seen in pith blocks and in red beet tissue were observed in the contents of pumpkin sieve tubes.

Journal Article↗
PubMed1995

Signal-to-motion artifact ratio versus frequency for impedance pneumography.

We measured transthoracic impedance between 12.5 and 185 kHz in nine adults. We used a system with two impedance channels, both simultaneously detecting the real part of impedance at two different frequencies. We used only two electrodes in the midaxillary line, connecting both channels in parallel. The amplitude relation between the two channels was measured for different maneuvers and frequencies. Results show for normal breathing an increase of the signal of 20% and a decrease in motion artifacts from 12.5 to 185 kHz. We conclude that, for the maneuvers studied, it is better to work at higher frequencies than the ones commonly used. Also, we suggest a method to further increase the signal-to-motion artifact ratio based on measurement at two frequencies.

Adult↗
PubMedDate not supplied

Reorganizing the lexicon by learning a new word: Japanese children's interpretation of the meaning of a new word for a familiar artifact.

This research investigated how children interpret the meaning of a new word associated with a familiar artifact. The existing literature has shown that syntactic form-class information plays an important role in making this kind of inference. However, this information is not available to Japanese children, because Japanese language does not have a grammatical distinction between count nouns and mass nouns, proper nouns and common nouns, or singular and plural. In Study 1, 12 three-year-old monolingual Japanese children were tested to examine whether they interpreted a new noun associated with a familiar artifact to be a material name or a new label for the object. They interpreted the new word as a new category label for the object, rather than as a name for the material. How children related the new category to the old familiar one was then examined in Studies 2 and 3. The results of Study 2, in which 24 three-year-olds participated, showed that children could flexibly shift between two interpretations using shape information. When the named object had a typical shape for the familiar category, they mapped the new word to a subordinate category. In contrast, when the shape of the named object was atypical, they mapped the new word to a new category that was mutually exclusive to the familiar category by excluding the named object from the familiar category. In Study 3, 12 three-year-olds were tested to examine relative importance of shape and functional information in this inference process. The results of the three studies suggest that children flexibly recruit clues from multiple sources, but the cluesare weighed in hierarchical order so that they can determine the single most plausible solution in a given situation when different clues suggest different solutions.

Child, Preschool↗
PubMed1988

Radioimmunoassay artifact associated with circulating anti-rabbit antibodies.

A 30 year old woman presenting with infertility was found to have elevated serum immunoreactive prolactin, TSH and total T3. These findings were eventually attributed to assay artifact when she was shown to have anti-rabbit antibodies in her serum. The possibility of laboratory artifact should be considered in clinical practice when abnormal immunoassay results are unsupported by clinical or radiographic data.

Adult↗
PubMed2005

How do parents respond to children's questions about the identity of artifacts?

We investigated how parents respond to young children's questions about the identity of artifacts. Children's questions were predominantly ambiguous about whether they were inquiring about name or function, but when their questions were more specific, they were almost always about function. For unfamiliar objects, parents responded with functional information the majority of the time, alone or in addition to names. For atypical members of familiar categories, adults usually responded only with the category name. The results indicate that adults adjust their responses in a way that often provides the information about object kind, specifically functional information in the case of artifacts, that they believe their children are lacking. Such input may contribute to the development of children's concepts and word meanings.

Adult↗
PubMed1982

Pacemaker spike alternans: an artifact of digital signal processing.

Marked variability in the amplitude or polarity of pacemaker artifacts may be a clue to generator malfunction or partial electrode fracture. We report a case where "pacemaker spike alternans" occurred factitiously as a result of a digital "roll-over" effect. The widespread introduction of digital electrocardiographs into clinical practice makes recognition of such artifacts important.

Aged↗
PubMed1990

The effect of suppression of the distortion artifact during transcutaneous pacing on the shape of the QRS complex.

The quality of the ECG recording during transcutaneous pacing was evaluated in six healthy volunteers. The transcutaneous pacing stimulator was an NP4D special unit to which was attached an electronic suppressor of artifact generated by the transcutaneous stimulating impulse. The relationship between this suppression of artifact distortion and the resulting QRS complex was analyzed. The results revealed that the suppression time (described as a 2-mm oscillation from 100-Hz frequency) was required for ECG distortion elimination and that this is dependent on the threshold of ventricular pacing. The width of the resulting QRS complex diminishes as the suppression is extended over 110 ms. These results suggest the necessity of individual adjustment of the suppression time so that the efficacy of transcutaneous pacing is adequately assessed.

Adult↗
PubMed2000

Partial wave analysis of the ultrasound comet tail artifact.

An adaptation of linear acoustic scattering theory is used to describe the comet tail artifact which is observed in the diagnostic ultrasound imaging of small spherical masses. The calculated backscattered pressure wave is shown to correspond well with the appearance of the artifact in a variety of clinical images.

Algorithms↗
PubMed2001

Correcting organ motion artifacts in x-ray CT medical imaging systems by adaptive processing. I. Theory.

X-ray CT scanners provide images of transverse cross sections of the human body from a large number of projections. During the data acquisition process, which usually takes about 1 s, motion effects such as respiration, cardiac motion, and patient restlessness produce artifacts that appear as blurring, doubling, and distortion in the reconstructed images, and may lead to inaccurate diagnosis. To address this problem several processing techniques have been proposed that require a priori knowledge of the motion characteristics. This paper proposes a method, which makes no assumptions about the properties of the motion, to eliminate the motion artifacts. The approach in this paper uses a spatial overlap correlator scheme to accurately track organ motion in computed tomography imaging systems. Then, it is shown that as optimum processing scheme to remove organ motion effects is to apply adaptive interference cancellation (AIC) methods, which treat the output of the spatial overlap correlator as noise interference at the input of the AIC process. Furthermore, an AIC method does not require any kind of periodicity of the motion effects. Synthetic data tests demonstrate the validity of this approach and show that hardware modifications are essential for its implementation in x-ray CT medical imaging systems.

Algorithms↗