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PubMed2002

Loss of heterozygosity and PCR artifacts in a microsatellite analysis of psoriasis and colorectal cancer.

Although a loss of heterozygosity (LOH) is commonly observed using microsatellite markers in a cell-proliferating malignant disorder, controversial findings of psoriasis, a keratinocyte-outgrowth disease, remain to be explained. It was hypothesized that unstable natures of the microsatellite markers for the polymerase chain reaction (PCR) might give a rise to either a false-positive or -negative LOH. Twenty-one frozen skin tissues and 33 formalin-fixed paraffin-embedded archives were obtained from patients with psoriatic plaques and colorectal cancers, respectively. In the frozen psoriatic skin, two of the 17 microsatellite markers selected from 11 chromosomal arms were associated with artifact LOHs that were not reproduced in repeated PCRs. The remaining 15 stable microsatellite markers with few PCR artifacts demonstrated a borderline-level LOH in cases with an ambiguous heterozygosity such as a juxtaposed allelic band. Infrequent LOHs (3 out of 242 heterozygous markers, 1.2%) were detected in psoriatic cases with two separate alleles. In colorectal cancers, a set of the 15 stable microsatellite markers identified a minimal borderline-level LOH at the cut-off point that was same with that of psoriasis. These results indicate that the selection of reproducible microsatellite sequences and the cautious criteria for informative heterozygosity are required to obtain the reliable LOH results from variable genomic DNAs, and that psoriatic lesions harbor few LOH.

Alleles↗

PubMed1995

Essentialism and graded membership in animal and artifact categories.

A number of studies have argued that people view membership in animal and artifact categories as a matter of degree. These studies have generally failed to distinguish between the issues of typicality and category membership. Thus, data which have been taken to demonstrate that membership is a matter of degree may only demonstrate that typicality is graded. Partly on the basis of these findings, it has been argued that some categories are organized around an underlying essence. The essence determines membership absolutely. The present paper reports a series of studies that reexamine the question of graded membership. In the first study, subjects were asked to rate both typicality and category membership for the same stimuli as a way of distinguishing the two questions. A second method relied on the intuition that disagreements about membership in all-or-none and graded categories may have different qualities. Results from both studies suggest some support for claims that membership in animal and artifact categories is a matter of degree. A third study explored the possibility that graded responses were due to conflicting, or ambiguous, sets of criteria. A task focusing on biological features did not lead to more absolute categorization. These results contradict essentialist predictions.

Adult↗

PubMed2000

Toward an explanation of the power law artifact: insights from response surface analysis.

The power law (y = ax-b) has been shown to provide a good description of data collected in a wide range of fields in psychology. R. B. Anderson and Tweney (1997) suggested that the model's data-fitting success may in part be artifactual, caused by a number of factors, one of which is the use of improper data averaging methods. The present paper follows up on their work and explains causes of the power law artifact. A method for studying the geometric relations among responses generated by mathematical models is introduced that shows the artifact is a result of the combined contributions of three factors: arithmetic averaging of data that are generated from a nonlinear model in the presence of individual differences.

Behavior↗

PubMed1990

Reduction of postoperative CT artifacts of pelvic fractures by use of titanium implants.

The value of CT scanning for both preoperative and postoperative assessment of pelvic and acetabular fractures has been demonstrated. Previous attempts at our institution to obtain useful pelvic CT scans following internal fixation with stainless steel implants have been impaired by metal artifacts that degraded the transaxial CT images. Our use of titanium, instead of stainless steel implants, produced identical fixation and ultimate fracture healing, but yielded minimal artifacts. We recommend the use of titanium implants as substitutes for stainless steel implants in pelvic fixation to maximize the information obtained on subsequent CT exams.

Bone Screws↗

PubMedDate not supplied

Artifacts of measuring during strabismus surgery.

Several different artifacts can induce errors in measurements obtained during strabismus surgery. Fixating the severed rectus muscle stump with forceps during strabismus surgery can result in a temporary anterior displacement of the insertion. This may result in inaccuracies in determining the site to which the muscle is to be recessed. This displacement was quantified in a prospective masked manner and was found in some patients to result in as much as 1 mm of error. It can be prevented by measuring the recession prior to fixating the insertion stump with forceps; however, it cannot always be prevented by measuring from the limbus, which also introduces other artifacts due to geometric principles. An "advancement effect" occurs during a rectus muscle recession due to the mechanics of suture placement in the muscle. It was quantified in a masked manner and found to be approximately .5 mm in most cases. A "V" shaped deformity of the insertion stump may occur immediately adjacent to the forceps. This deformity frequently distorts the insertion by as much as several millimeters.

Humans↗

PubMed1984

The ghost artifact.

A ghost artifact is produced when refraction of an ultrasound beam occurs in one part of a scanning plane. Image duplication or even triplication may result. This may lead to error of diagnosis and measurement. Ghost artifacts are commonly seen in transverse echograms of pelvic organs because the rectus muscle interposed between the transducer and the area of interest is acting as a lens and refracts the ultrasound beam. Three illustrative case reports are presented.

Adult↗

PubMed1989

Duplication of the aortic ring. An artifact in echocardiography.

Duplication or widening of the aortic ring is commonly observed in echocardiography. This imaging artifact arises from refraction of a portion of the sound beam by an unossified costal cartilage in the anterior chest wall. When the cartilage is situated in line with the edge of the aortic ring or just lateral to it, the artifact is produced. Given the anatomy of the costal cartilages, chest wall, and heart, the amount of refraction is calculated and compared with the amount of refraction actually observed in scans. The degree of duplication or widening of the aortic ring depends directly on the curvature of the costal cartilage and the distance between the cartilage and the aortic ring.

Cartilage↗

PubMed1990

The carotid ghost. A color Doppler ultrasound duplication artifact.

Color Doppler ultrasound examinations of the neck frequently demonstrate an artifactual region of color assignment deep to the common carotid artery that simulates blood flow in deep cervical arteries. Based on analysis of imaging performed on 10 normal volunteers, it was shown that the pulsed Doppler waveform originating from the artifact was identical to that of the common carotid artery. It was also shown that the artifact was always located deep to the common carotid artery regardless of location and positioning of the transducer. In vitro modeling using a flow phantom confirmed that the appearance was artifactual in nature. The mechanism of production most likely is related to a mirroring phenomenon at the deep wall of the common carotid artery.

Blood Flow Velocity↗

PubMed1999

Mice Fed Radiolabeled Protein by Gavage Show Sporadic Passage of Large Quantities of Intact Material Into the Blood, an Artifact not Associated With Voluntary Feeding.

Bovine 2-microglobulin (Bov 2-M) is a small acid- and protease-resistant protein found in cows' milk that has the capacity to interact specifically with molecules of the mouse immune system. We conducted a series of investigations designed to determine whether a portion of orally ingested Bov 2-M could pass intact into the mouse circulatory system. Initial experiments feeding 125I-labeled protein by gavage to nonfed mice indicated that intact Bov 2-M appeared rapidly and at high amounts in the blood (as detected by use of direct sodium dodecyl polyacrylamide gel electrophoresis analysis of a 1-ml sample of plasma and phosphorimaging), but this result was observed sporadically and only in about a third of all animals, with no detectable protein appearing in the plasma of the remaining animals. Identical results were obtained when the mice were lightly anesthetized prior to gavage. When a larger protein, 125I-labeled bovine serum albumin (BSA), was fed by gavage in combination with the labeled Bov 2-M, surprisingly large fragments of the BSA (. 50 kDa) appeared in the plasma whenever the Bov 2-M appeared, again in about a third of the animals. We hypothesized that the passage of large quantities of Bov 2-M into the blood of some mice was due to an intermittent artifact of the gavage feeding (likely spillover into the lungs), and therefore, we developed an alternate approach based on voluntary feeding. Mice were easily taught to drink small samples of liquid voluntarily by removing water for 12 h, then manually generating droplets at the end of a 1-ml syringe. When a mixture containing 125I-labeled Bov 2-M and BSA was fed in this manner, labeled protein could not be detected in any animals by direct analysis of a 1-ml sample of plasma. However, when immunoprecipitation was carried out on a larger volume of plasma (100 ml), intact Bov 2-M could be found in the blood of all animals, whereas similar immunoprecipitation and analysis for BSA did not yield any signal. We conclude that the common method of gavage feeding mice to assess absorption of orally ingested material can lead to artifacts not seen when the same agent is consumed under more natural circumstances. These observations may have relevance for experiments where oral tolerance is assumed to be induced in rodents by repeated gavage feeding, whereas the same effects cannot be obtained in humans by voluntary feeding.

Journal Article↗

PubMed1976

"EAR" artifact in brain scans.

The ear closest to the camera may be imaged in high-resolution lateral views of the brain as a structure anterior to the lateral sinus. The artifact can usually be eliminated by taping the auricle down. Artifacts such as this can be expected to become somewhat more of a problem as image resolution improves.

Brain Diseases↗

PubMed1992

The size of small cell lung carcinoma cells. Ratio to lymphocytes and correlation with specimen size and crush artifact.

The size of small cell lung carcinoma (SCLC) cells has often been ambiguously defined as one and a half to four times that of a lymphocyte. The purpose of this study was to determine the ratio of nuclear diameter (ND) of SCLC cells to that of lymphocytes in the same tissue sections and to assess whether the size of SCLC cells correlates with the size of tumor specimens and crush artifact. The overall mean ND (microns +/- SD) of SCLC cells was 9.2 +/- 2.1, found in 36 oat cell carcinomas (OAT, 1,800 nuclei) and 16 intermediate cell carcinomas (INT, 800 nuclei). The mean ND of OAT and INT cells was 8.1 +/- 1.3 and 11.6 +/- 1.5, respectively. The mean ND of lymphocytes (2,600 nuclei) was 5.2 +/- 0.3. The overall mean of ND ratios (+/- SD) between SCLC cells and lymphocytes was 1.8 +/- 0.4 (median, 1.7), 1.6 +/- 0.2 for OAT and 2.2 +/- 0.3 for INT. The mean size of the 52 SCLC biopsy specimens was 0.6 +/- 0.9 cm. Of all the biopsies, 84.6% (n = 44) showed various degrees of tissue crushing. The ND of SCLC cells was associated with specimen size (P = .004) and the degree of tissue crushing (P = .001). Therefore, our findings further support the hypothesis that OAT should be considered the effect of artifact rather than a true variant of SCLC and that the ND of SCLC cells is approximately two times that of lymphocytes.

Analysis of Variance↗

PubMed2006

Increased residual variance at developmental switch points: statistical artifact or indicator of exposed genotypic influence?

Discussing the organization of developmental switches, West-Eberhard (2003) proposed the use of regression residual plots to locate the neutral point of the switch, which is characterized by maximum genotypic influence on the resulting phenotype. However, statistical artifacts due to measurement error in nonlinear models might account for a substantial proportion of the increase of residuals variance at the switch point. Simulations based on field data show that increases in residual variance occur as artifacts when normal amounts of measurement error are present, even in absence of any genotypic variance. The results suggest that interpretation of nonlinear variation in thresold traits is problematic and requires considering this statistical effect. A method to estimate the weight of genotypic contribution to residual variance is proposed, and its assumptions and limitations are discussed.

Animals↗

PubMed2006

[The artifacts and test-retest reliability of multiple auditory steady-state response].

OBJECTIVE: To investigate the characteristics and clinical application of artifacts and the test-retest reliability of multiple auditory steady-state response (MASSR). METHOD: The authors tested a group of healthy young volunteers and a group of patients with sensory hearing loss with the MASSR by analysing the rate of false negative artifacts (FNA) and their distribution. The healthy young volunteers were retested with MASSR several days after the first test to investigated the test retest reliability of MASSR. Furthermore, three cases of healthy young volunteers were retested in the sleeping status to explore the stability of MASSR threshold and the influence of sleep. RESULT: (1) The FNA mainly distributed in low frequencies districts and the intensities were near threshold, no remarkable differences could be seen between the normal ears and the ear with sensory hearing loss. The FNA disappeared when the volunteers were asleep. (2) The test-retest variability was much higher in 0.5 kHz than in other frequencies. The variable range was 0 - 30 dB in 0.5 kHz, and there was test-retest reliability in 1.0-4.0 kHz. (3) The artificial response was present when using strong stimulus for the patients with profound hearing loss. When MASSR was recorded in awake condition, the FNA appeared. When using strong stimulus for the cases with profound hearing loss, the artificial response existed and the test-retest variabilities were large. The whole test duration was often much longer than the auditory brainstem response (ABR) and 40 Hz auditory evoked potential (40 Hz AEP). CONCLUSION: As an objective auditory evaluation method, MASSR scarcely has superior characteristics to ABR and 40 Hz AEP.

Adolescent↗

PubMed1991

Slice selection axis motion artifact correction in MRI.

In magnetic resonance imaging using two-dimensional Fourier transform techniques, motion causes ghosting in the phase-encoded direction and loss of image resolution. Although numerous techniques have been proposed to suppress these motion artifacts, they are a continuing problem. In this paper a new technique is presented to reduce the artifact from motion along the slice selection axis. It is shown that such motion causes an amplitude modulation of the data, and an iterative algorithm is developed to reduce this modulation by post-processing the data using signal processing techniques. The algorithm is tested on simulated data, and shown to perform well, even with significant levels of noise added to the data.

Algorithms↗

PubMed1991

An investigation of the magnitude and causes of count loss artifacts in SPECT imaging.

A quantitative evaluation and an investigation of the mechanism of the count losses that can occur in SPECT imaging is described. The most common clinical example of the artifacts which result from this is encountered when sections are taken through the femoral heads in skeletal studies of the pelvis. From some simple phantom studies, it was identified that the count losses were associated with the presence of a high dynamic range in the projection data. Further information was obtained from simulation studies. It was found that the count loss phenomenon is caused by the combined effects of the presence of a high count density area and a structure with a relatively high attenuation level. An appreciation of the presence, magnitude, and mechanism of this effect is important if erroneous clinical findings are to be avoided. This is particularly relevant because of the existence of a variety of techniques that can be used to remove the resulting artifacts.

Bone and Bones↗

PubMedDate not supplied

Effects of magnetic susceptibility artifacts and motion in evaluating the cervical neural foramina on 3DFT gradient-echo MR imaging.

The purpose of this study was to evaluate in vitro the effects of magnetic susceptibility and motion on the estimation of neural foraminal diameter with three-dimensional Fourier transformation (3DFT) gradient-recalled MR imaging as compared with CT. A cervical spine phantom was constructed from desiccated human cervical vertebral bodies embedded in a water-based proteinaceous gel. The phantom was imaged with thin-section 1.5-mm axial CT and 1.5-mm axial 3DFT gradient-recalled MR using a constant TR (35 msec) and flip angle (5 degrees), while the TE was varied from 11 to 22 msec. During imaging, the phantom either was kept stationary or underwent subtle, intermittent motion. Compared with CT, MR consistently underestimated the diameters of the neural foramina, leading to overestimation of neural foraminal stenosis. The degree of over-estimation varied directly with increasing TE values, from 8% (TE = 11 msec) to 27% (TE = 22 msec). Motion artifacts also increased foraminal overestimation and mimicked osseous hypertrophy. The effect of image degradation due to motion was noted to increase with longer TE values. Image degradation caused by magnetic susceptibility and motion artifacts can be minimized by using the shortest TE possible. We do not recommend the use of 3DFT gradient-recalled MR imaging for the evaluation of cervical radiculopathy if patient motion is anticipated.

Cervical Vertebrae↗

PubMedDate not supplied

Pseudoatrophy of the cervical portion of the spinal cord on MR images: a manifestation of the truncation artifact?

Routine evaluation of axial MR images of the cervical spine with high-intensity CSF (long TR/TE spin-echo or gradient-echo images) revealed apparent narrowing of the cord's anteroposterior diameter when these images were compared with corresponding postmyelography CT scans. This discrepancy was believed to be due to the truncation artifact at the CSF-cord boundary. To examine the truncation effect, we compared cord diameters in 12 patients on postmyelography CT scans and MR images and then compared these with MR scans of normal volunteers and of an agar-saline spine phantom. There was an artifactual diminution of the cord diameter in the 128-step phase-encoding axis of the 128 x 256-matrix MR scan as compared with the diameter of the cord in the patients' postiohexol CT scans and in the 256 phase-encoded axis MR scan in the volunteer study. A similar discrepancy was noted in the spine phantom study, in which the cord diameter in the 256-step phase-encoded MR scan, the CT scan, and direct measurement exceeded that in the 128-step phase-encoded axis MR scan. The range of differences between the measurements was as large as 2.3 mm (patients), 1.7 mm (volunteers), and 1.8 mm (phantom) for the three studies. In all three studies, varying the photographic window width and level produced variation in the apparent cord diameter of up to 1.5 mm. To eliminate this effect, the cord diameters in the phantom and the normal control subjects were measured at identical window levels. The truncation artifact, coupled with standard window settings used in photography, may lead to inaccurate display of the diameter of the cervical spinal cord.

Humans↗

PubMed1990

On the distinction between artifacts and information.

Sperling, Landy, Dosher, and Perkins (1989) argued that all previous research on the kinetic depth effect has been contaminated by stimulus artifacts, and they developed a new task that they believe can successfully overcome this problem. The present discussion offers a counter-argument that artifacts are not as pervasive in previous research as Sperling et al. imply and that their proposed method is subject to precisely the same limitations as earlier studies. Also discussed are some general guidelines of experimental design in this type of research to minimize the possibility that subjects will adopt an inappropriate response strategy that does not truly reflect their visual perceptions of three-dimensional form.

Acceleration↗