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PubMedDate not supplied

Radiological laser film scanner sampling artifact.

Artifacts seen on laser digitized radiographs are analyzed and mathematically explained based on the concept of image contrast. Our investigation considered the following determinants: (a) laser spot size, (b) signal processing components, (c) image characteristics, and (d) observer performance. A functional relationship between the sampling interval, laser spot size, and the contrast of the artifact seen on the digitized image is derived. This relationship is verified experimentally using a variable spot size laser source and sampling at interval of 175.0 microns. The problem of digitizing artifact seen on film images obtained with anti-scatter grids is discussed.

Analog-Digital Conversion↗
PubMed2004

Kinematical models to reduce the effect of skin artifacts on marker-based human motion estimation.

The estimation of the skeletal motion obtained from marker-based motion capture systems is known to be affected by significant bias caused by skin movement artifacts, which affects joint center and rotation axis estimation. Among different techniques proposed in the literature, that based on rigid body model, still the most used by commercial motion capture systems, can smooth only part of the above effects without eliminating their main components. In order to sensibly improve the accuracy of the motion estimation, a novel technique, named local motion estimation (LME), is proposed. This rests on a recently described approach that, using virtual humans and extended Kalman filters, estimates the kinematical variables directly from 2D measurements without requiring the 3D marker reconstruction. In this paper, we show how such method can be extended to include the computation of the local marker displacement due to skin artifacts. The 3D marker coordinates, expressed in the corresponding local reference coordinate frames, are inserted into the state vector of the filter and their dynamics is automatically estimated, with adequate accuracy, without assuming any particular deformation function. Simulated experiments of lower limb motion, involving systematic mislocations (5, 10, 20 mm) and random errors of the marker coordinates and joint center locations (+/-5, +/-10, +/-15 mm), have shown that artifact motion can be substantially decoupled from the global skeletal motion with an effective increase of the accuracy wrt standard techniques. In particular, the comparison between the nominal kinematical variables and the one recovered from markers attached to the skin surface proved LME to be sensibly superior (50% in the worse condition) to the methods imposing marker-bone rigidity. In conclusion, while requiring further validation on real movement data, we argue that the proposed method can constitute an appropriate approach toward the improvement of the human motion estimation.

Biomechanical Phenomena↗
PubMed2004

New discoveries and interpretations of hominid fossils and artifacts from Vindija Cave, Croatia.

Beginning with excavations during the 1970s, Vindija Cave (Croatia) has yielded significant Middle and Upper Paleolithic fossil and archaeological finds. We report on seven recently identified hominid fossils, a newly associated partial hominid cranial vault from level G(3), nine possible bone retouchers, and a revised interpretation of the Mousterian artifact assemblage from the site. This new information reinforces our knowledge of the complex biocultural phenomena revealed in unit G and earlier deposits at Vindija. Six of the new hominid fossils derive from stratigraphic units G and I, while one lacks exact provenience. All specimens preserving diagnostic anatomy are from Neandertals. One of the postcranial remains, a radius fragment which exhibits Neandertal-like anatomy, comes from level G(1)and is congruent with the previously established association of Neandertals with an early Upper Paleolithic industry at the site. The partial cranial vault represents the most complete Neandertal from Vindija. The possible retouchers derive from unit G. Our analysis of these artifacts suggests that both percussion and pressure techniques may have been used by Neandertals in the final stage of tool production (retouching). This paper also presents a revision of the artifact analysis for late Mousterian level G(3). We separated raw materials into two main groups due to the differing ways that the materials fracture and the differing morphology of the debitage. The use of raw material in level G(3)is different from earlier Middle Paleolithic levels at Vindija. This indicates that the G(3)late Neandertals were making choices regarding source material somewhat more like the Upper Paleolithic people at the site. When interpreted within a larger regional framework, the Vindija archaeological and hominid fossil remains demonstrate a complex, mosaic pattern of biocultural change in the Late Pleistocene of south-central Europe.

Animals↗
PubMedDate not supplied

Positron emission tomography/computed tomography--imaging protocols, artifacts, and pitfalls.

There has been a longstanding interest in fused images of anatomical information, such as that provided by computed tomography (CT) or magnetic resonance imaging (MRI) systems, with biological information obtainable by positron emission tomography (PET). The near-simultaneous data acquisition in a fixed combination of a PET and a CT scanner in a combined PET/CT imaging system minimizes spatial and temporal mismatches between the modalities by eliminating the need to move the patient in between exams. In addition, using the fast CT scan for PET attenuation correction, the duration of the examination is significantly reduced compared to standalone PET imaging with standard rod-transmission sources. The main source of artifacts arises from the use of the CT-data for scatter and attenuation correction of the PET images. Today, CT reconstruction algorithms cannot account for the presence of metal implants, such as dental fillings or prostheses, properly, thus resulting in streak artifacts, which are propagated into the PET image by the attenuation correction. The transformation of attenuation coefficients at X-ray energies to those at 511 keV works well for soft tissues, bone, and air, but again is insufficient for dense CT contrast agents, such as iodine or barium. Finally, mismatches, for example, due to uncoordinated respiration result in incorrect attenuation-corrected PET images. These artifacts, however, can be minimized or avoided prospectively by careful acquisition protocol considerations. In doubt, the uncorrected images almost always allow discrimination between true and artificial finding. PET/CT has to be integrated into the diagnostic workflow for harvesting the full potential of the new modality. In particular, the diagnostic power of both, the CT and the PET within the combination must not be underestimated. By combining multiple diagnostic studies within a single examination, significant logistic advantages can be expected if the combined PET/CT examination is to replace separate state-of-the-art PET and CT exams, thus resulting in significantly accelerated diagnostics.

Humans↗
PubMed1983

Artifacts introduced by spectacle lenses in the measurement of strabismic deviations.

The peripheral prismatic effects of corrective spectacle lenses introduce an artifact when strabismic deviations are measured. Plus lenses decrease and minus lenses increase the measured deviation. This effect begins to become clinically significant with corrective lenses with powers of more than +/- 5 diopters. We developed a simplified model that predicts the magnitude of this effect. The model agreed with actual ray tracing analysis through commonly used spectacle lenses and also agreed closely with clinical data. The clinical use of this model is facilitated by remembering the artifacts produced by +20, +10, -10, and -20 diopter spectacle lenses and interpolating for intermediate values. Correcting for these artifacts should enhance the predictability of strabismus surgery in patients with significant ametropia.

Eyeglasses↗
PubMed2003

Formation of an artifact of diclofenac during acidic extraction of environmental water samples.

Solid-phase extraction at an acidic pH is used as a common sample preparation method for analyzing residues of the analgesic drug diclofenac (2-[(2,6-dichlorophenyl)amino] benzeneacetic acid) in environmental water samples. This paper describes the matrix-dependent formation of an artifact of diclofenac during sample preparation resulting in an up to 40% underestimation of diclofenac concentrations especially in matrix-prone samples such as sewage effluents or surface water. The artifact most likely being formed during acidification of the sample was unequivocally identified as 1-(2,6-dichlorophenyl)indolin-2-one by capillary gas chromatography-mass spectrometry. To avoid an underestimation of the analytical results quantification of both diclofenac and its artifact is recommended.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed1989

Lens rim artifact in automated threshold perimetry.

In central static threshold visual fields (Humphrey 30-2 Program) performed with a corrective lens, lens rim artifact (LRA) was present in 10.4% of 704 fields examined retrospectively and 6.2% of 276 fields evaluated prospectively. Lens rim artifact most commonly presented as a combination of absolute and relative defects involving the temporal quadrant either alone or in combination with another quadrant. Lens rim artifact was related to seven different types of interpretational errors, five of which led to an overdiagnosis and two to an underdiagnosis. Risk factors for the occurrence of LRA include older age, high hyperopic correction, and location specific involvement probably due to a limitation in perimeter design. Field defects involving only the four targets at 27 degrees eccentricity in the temporal quadrant were due only to LRA in this series and may be disregarded when interpreting the Humphrey 30-2 Program. Recommendations are made toward minimizing the occurrence of LRA and avoiding interpretational errors associated with LRA.

Adult↗
PubMed2002

A mixed approach to artifacts minimization in a continuous-rotate X-ray based tomographic imaging system using linear detector array.

Adaptation of a general-purpose digital radiographic scintillator-based linear detector array (LDA) in a continuous-rotate third generation X-ray industrial tomographic imaging system and the resulting artifacts are discussed. Sources of error in the projection data are identified and a mixed approach, involving neighborhood averaging and row-wise application of a low-pass filter for the minimization of artifacts in the reconstructed images using weighted convolution back projection algorithm is illustrated. It is observed that the recently launched LDA can easily be adapted for industrial tomographic imaging of low-density specimen in a cost effective way by incorporating the suggested artifact removal technique in the given configuration.

Journal Article↗
PubMed2003

The sources of young children's name innovations for novel artifacts.

Two studies investigated whether four-year-old children (12 in Experiment 1 with a mean age of 4;8 and 36 in Experiment 2 with a mean age of 4;7) invent names for new artifacts based on the objects' functions as opposed to their perceptual properties. Children informed about the intended functions of novel objects provided more name innovations that were clearly function-based than perception-based. This tendency was observed when children were shown the objects' functions, even if they were also given verbal descriptions of the objects' perceptual properties and parts. Only when ignorant of the objects' intended functions did children tend to use perceptual features to create substantial numbers of names. Accordingly, results from this name-innovation methodology converge with findings from some recent studies of lexical categorization suggesting that functional information is critical to how preschoolers extend artifact names. Children appear to appreciate an intimate relation between the functions of artifacts and how they are named.

Analysis of Variance↗
PubMed1999

Iterative X-ray Cone-Beam Tomography for Metal Artifact Reduction and Local Region Reconstruction.

: X-ray cone-beam reconstruction from incomplete projection data has important practical applications, especially in microtomography. We developed expectation maximization (EM)-type and algebraic reconstruction technique (ART)-type iterative cone-beam reconstruction algorithms for metal artifact reduction and local reconstruction from truncated data. These iterative algorithms are adapted from the emission computerized tomography (CT) EM formula and the ART. A key step in our iterative algorithms is introduction of a projection mask and computation of a 3-D spatially varying relaxation factor that allows compensation for beam divergence and data incompleteness. The algorithms are simulated with projection data synthesized from mathematical phantoms. In simulation, the EM-type and ART-type iterative algorithms are demonstrated to be effective for metal artifact reduction and local region reconstruction. They perform similarly in terms of visual quality, image noise, and discrepancy between measured and reprojected data. The EM-type and ART-type iterative cone-beam reconstruction algorithms have potential for metal artifact reduction and local region reconstruction in X-ray CT.

Journal Article↗
PubMed1983

Artifacts due to movement in rotational panoramic radiography.

Image quality due to movement of the patient during the exposure is a common problem in conventional radiography. The resulting artifacts in the image are characteristic and easily identifiable blurring. The unique mechanics of image production and the prolonged exposure time used in rotational panoramic radiography can cause very different disturbances in the diagnostic image. The illustrations presented here are extreme examples of such artifacts, selected for clear illustration in a printed image. The challenge to the clinician is to identify the full spectrum of such distortions, from the obvious ones to the much more subtle effects of similar minor distortions that may not be so easily recognized as artifacts.

Head↗
PubMed2002

Artifacts, assumptions, and ambiguity: Pitfalls in comparing experimental results to numerical simulations when studying electrical stimulation of the heart.

Insidious experimental artifacts and invalid theoretical assumptions complicate the comparison of numerical predictions and observed data. Such difficulties are particularly troublesome when studying electrical stimulation of the heart. During unipolar stimulation of cardiac tissue, the artifacts include nonlinearity of membrane dyes, optical signals blocked by the stimulating electrode, averaging of optical signals with depth, lateral averaging of optical signals, limitations of the current source, and the use of excitation-contraction uncouplers. The assumptions involve electroporation, membrane models, electrode size, the perfusing bath, incorrect model parameters, the applicability of a continuum model, and tissue damage. Comparisons of theory and experiment during far-field stimulation are limited by many of these same factors, plus artifacts from plunge and epicardial recording electrodes and assumptions about the fiber angle at an insulating boundary. These pitfalls must be overcome in order to understand quantitatively how the heart responds to an electrical stimulus. (c) 2002 American Institute of Physics.

Journal Article↗
PubMed1996

The origin of skin-stretch-caused motion artifacts under electrodes.

The outside of the skin of the forearm is typically 15 mV more negative than the inside. Stretching the skin causes a reduction in the magnitude of this skin potential V, which we observe as a motion artifact delta V. We seek to determine the origin of this motion artifact by successively stripping 12 layers of the skin using Scotch Tape. Between each stripping we measure artifact delta V, 13 Hz impedance Z, and change in impedance delta Z. On the interior surface of the forearm, Z decreases with number of strippings. delta Z can be first either positive or negative, then is always negative and decreases linearly with Z. delta V first remains constant and then decreases with Z and delta Z. delta V and delta Z increase with stretch force following a logarithmic relationship. delta Z has a rectangular shape waveform, whereas the rising edge of delta V shows a fast followed by a slow component and its falling edge decays exponentially with a large time constant. We have expanded the model of Thakor and Webster to best fit the waveform of delta V and delta Z caused by stretch.

Adult↗
PubMed2005

Rate asymmetry after genome duplication causes substantial long-branch attraction artifacts in the phylogeny of Saccharomyces species.

Whole-genome duplication (WGD) produces sets of gene pairs that are all of the same age. We therefore expect that phylogenetic trees that relate these pairs to their orthologs in other species should show a single consistent topology. However, a previous study of gene pairs formed by WGD in the yeast Saccharomyces cerevisiae found conflicting topologies among neighbor-joining (NJ) trees drawn from different loci and suggested that this conflict was the result of "asynchronous functional divergence" of duplicated genes (Langkjaer, R. B., P. F. Cliften, M. Johnston, and J. Piskur. 2003. Yeast genome duplication was followed by asynchronous differentiation of duplicated genes. Nature 421:848-852). Here, we test whether the conflicting topologies might instead be due to asymmetrical rates of evolution leading to long-branch attraction (LBA) artifacts in phylogenetic trees. We constructed trees for 433 pairs of WGD paralogs in S. cerevisiae with their single orthologs in Saccharomyces kluyveri and Candida albicans. We find a strong correlation between the asymmetry of evolutionary rates of a pair of S. cerevisiae paralogs and the topology of the tree inferred for that pair. Saccharomyces cerevisiae gene pairs with approximately equal rates of evolution tend to give phylogenies in which the WGD postdates the speciation between S. cerevisiae and S. kluyveri (B-trees), whereas trees drawn from gene pairs with asymmetrical rates tend to show WGD pre-dating this speciation (A-trees). Gene order data from throughout the genome indicate that the "A-trees" are artifacts, even though more than 50% of gene pairs are inferred to have this topology when the NJ method as implemented in ClustalW (i.e., with Poisson correction of distances) is used to construct the trees. This LBA artifact can be ameliorated, but not eliminated, by using gamma-corrected distances or by using maximum likelihood trees with robustness estimated by the Shimodaira-Hasegawa test. Tests for adaptive evolution indicated that positive selection might be the cause of rate asymmetry in a substantial fraction (19%) of the paralog pairs.

Evolution, Molecular↗
PubMed1987

Artifact associated with the use of strong iodine solution (Lugol's) in cone biopsies.

The preoperative application of strong iodine solution (USP), commonly referred to as Lugol's solution, induces a histologic artifact in epithelial cells of cone biopsy material, most pronounced in dysplastic cells. Cellular shrinkage, cytoplasmic eosinophilia and vacuolization, development of visible intercellular space, and nuclear pyknosis with loss of chromatin detail are the major findings. Since the use of strong iodine solution (USP) is a common practice for delineating the ectocervical extent of disease prior to cone biopsy, the pathologist should recognize the artifact since its presence can make histologic interpretation difficult. Because the artifact may lead to interpretation error, alternatives to strong iodine solution (USP) should be considered.

Biopsy↗
PubMed1978

"Lunch syndrome," a bone-scanning artifact: case report.

After a photon-deficient area in the region of the stomach under the ribs on the left side was noted in some bone-scanning patients, a successful attempt was made to produce the artifact by having a cooperative patient eat a large lunch. The comparison of the scans before and after lunch showed the presence of a postprandial artifact in the area in question. It is important not to confuse this artifact with a space-occupying avascular mass in that part of the abdomen.

Adenocarcinoma↗
PubMed1982

Incidence and consequences of breast artifacts in radionuclide cardiac studies.

A retrospective evaluation was done on 426 radionuclide cardiac studies performed on female patients at our institution from January through September, 1980. These procedures included pyrophosphate (PYP) myocardial scans, resting and exercise Tl-201 studies, and gated equilibrium studies. The purpose of this evaluation was to document the incidence and possible consequences of breast artifacts in various cardiac procedures. We found the incidence to range from 30 to 50% of the studies performed, and both the incidence and type of artifact encountered varied with the type of procedure performed. Furthermore, 13 to 35% of patients had artifacts directly overlying the myocardium. The possible consequences, including potential misdiagnosis, interference with computer derived quantitative parameters, and the technical maneuvers necessary to avoid or alleviate these problems are discussed.

Breast↗