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PubMed1985

Chemical shift artifact in clinical magnetic resonance images at 0.35 T.

A thin, low-intensity line, which partially surrounds many structures on magnetic resonance imaging (MRI), is an artifact due to the phenomenon of chemical shift and should not be mistaken for a normal or abnormal morphologic structure. This artifact can be recognized by its characteristic appearance perpendicular to the direction of the frequency-encoding gradient at the interface of tissues with different chemical shift properties. Confinement within or extension beyond this thin, low-intensity line cannot be used as a criterion for staging neoplasms. Once recognized, the chemical shift artifact should not impede the use of MRI for clinical imaging at 0.35 T.

Diagnostic Errors↗

PubMed1977

The "eardrum artifact" in ipsilateral reflex measurements.

A source of error in ipsilateral reflex measurements with impedance methods is explained. It is shown that the inherent non-linearity of the cavity represented by the ear canal and tympanic membrane gives rise to an artifact in the measurement of acoustic impedance which is synchronous with the stimulus. The magnitude of the artifact increases with the intensity of the stimulus, but is relatively insensitive to the frequency of the stimulus. A practical method for measuring the magnitude of the artifact is described.

Acoustic Impedance Tests↗

PubMed1983

Clinical manifestations of the comet tail artifact.

The comet tail artifact appears as a dense tapering trail of echoes just distal to a strongly reflecting structure. This reverberation type of artifact occurs when there is a marked difference in acoustic impedances between an object and its surround. This paper presents a spectrum of comet tail artifacts seen in clinical practice and discusses their usefulness in decision making.

Foreign Bodies↗

PubMed1985

The ring-down artifact.

"Ring-down" is an ultrasound artifact that appears as a solid streak or a series of parallel bands radiating away from abdominal gas collections. Using an in vitro system of bubbles in water or gelatin, it was found that the ring-down artifact originated from the center of a cluster of four bubbles (bubble tetrahedron), three on top and one nestled beneath. Entrapped between the bubbles is a horn- or bugle-shaped fluid collection that we theorize emits a continuous sound wave back to the transducer when struck by an ultrasound pulse. Electronic processing by the scanner converts this continuous sound wave into the series of bands seen in the ring-down artifact.

Gases↗

PubMed1986

The retrolenticular afterglow: an echo enhancement artifact.

A mathematical model for a sonogram containing a circular object with a sonic speed less than that of its surroundings was constructed. The circular object acts as a lens to the ultrasound beam, which explains the refractive artifacts often observed. An unexpected artifact is also predicted, a region of increased echogenicity, which the authors named the retrolenticular afterglow, since it occurs behind a lens-like structure. An experiment was designed to show the appearance of this artifact occurring distal to an ethyl alcohol-filled cylindrical well in a tissue equivalent phantom.

Gallbladder↗

PubMed1990

Color Doppler artifact in anechoic regions.

For color Doppler imaging, several types of signal processing are employed in order to produce acceptable images of blood flow in blood vessels while suppressing color in moving solid tissue. The processing can produce an artifact in which color may arise from noise or from tissue motion and fill anechoic regions preferentially. This artifact may complicate the differentiation of areas with blood flow from anechoic regions without flow. By using four different color Doppler ultrasound units to image a tissue-equivalent phantom containing anechoic cylinders, artifactual color resulted when gain was raised sufficiently. This color was concentrated in anechoic regions of a gray-scale image that did not contain flow. In two instruments, this artifact was only observed when the transducer was vibrated, simulating tissue motion. In these instruments, the identification of low-frequency, high-amplitude Doppler signals is used to locate moving solid tissue and so suppress color in these regions. In the other two instruments, the presence of echoes within the image suppressed the assignment of color. With both types of processing, color may appear artifactually in echo-free regions without flow, such as fluid collections. Presence or absence of flow should be confirmed by Doppler spectral analysis. An understanding of the origin and appearance of artifactual color can prevent its occurrence from detracting from the usefulness of color Doppler imaging.

Aorta, Abdominal↗

PubMed2000

A new artifact-free device for frameless, magnetic resonance imaging-guided stereotactic procedures.

OBJECTIVE: A new, artifact-free, nonobstructive device was required for planning, guiding, and performing stereotactic procedures in an open magnetic resonance imaging (MRI) system (Signa SP; General Electric, Milwaukee, WI). DESCRIPTION OF INSTRUMENTATION: We devised an MRI-compatible instrument set that was adapted to an optical triangulation system (FlashPoint System; Image Guided Technologies, Boulder, CO) and consisted of a Pathfinder for planning burr holes and trajectories and a Snapper-Stereoguide for guiding minimally invasive instruments such as biopsy cannulae, endoscopes, and laser fibers. The instruments were composed of biocompatible plastic (polyacetal). During evaluation, special attention was paid to safety, accuracy, operation times, and susceptibility artifacts of the system. RESULTS: The first 20 stereotactic procedures performed in the open MRI scanner included 15 biopsies, 1 cyst and 3 abscess evacuations, and 1 endoscopic procedure for treatment of multiseptate hydrocephalus. There were no adverse outcomes, and all biopsies were diagnostic. The frameless stereotactic system in combination with the FlashPoint System proved to be accurate, with a mean error of 1.5 mm. The biopsy devices did not cause any susceptibility artifacts. Highly vascularized structures were clearly visible and were included in the trajectory planning. With experience, the procedure time was reduced to less than 1 hour. CONCLUSION: This device was found to be quite helpful for planning and guiding stereotactic procedures in the open MRI scanner. Nearly real-time planning and monitoring of stereotactic procedures and the positional accuracy of the system make the open MRI system a definite improvement, compared with conventional stereotactic systems.

Adolescent↗

PubMed2001

Fenfluramines, idiopathic pulmonary primary hypertension and cardiac valve disorders: facts and artifacts.

The fenfluramines saga began in 1963 and ended in 1997. Fenfluramines are anorexigenic agents recommended, in April 1996, for the long-term treatment of obesity in USA, before being suddenly withdrawn from the market in September 1997. Over 34 years, about 60 million people were exposed to these drugs worldwide, mainly in Europe. The aim of this critical review is not to attempt to rehabilitate these appetite suppressants but to launch a plea for a more rational and rigorous approach to what might be called objective medical knowledge. Idiopathic primary pulmonary hypertension and cardiac valve disorders which have been both associated with fenfluramines have in common many puzzling features. The metamorphosis of facts into artifacts is only a hypothesis, but seems conceivable from a scientific point of view. Medicine is not only an art, it is also a science, which, like the others, implies adhesion to certain fundamental rules, such as refutation or verification of all experimental results by rigorous and standardized methods, before considering them as established facts. Firstly, a single study, moreover a case-control study like the International Primary Pulmonary Hypertension Study, is not sufficient to establish a causal relationship between exposure to appetite-suppressants and idiopathic pulmonary hypertension, because of the numerous biases which characterize even the best analytical research. Secondly, Doppler-echocardiography cannot be considered as a laboratory test, because of the poor interoperator reproducibility observed in obese patients. The use of this technique in pharmaco-epidemiology implies standardized procedures concerning not only reading data, but also their acquisition, because of possible uncontrolled interactions between sonographers, patients and sophisticated machines. In the case of the fenfluramines saga, numerous methodological artifacts concerning acquisition, processing and interpretation of epidemiologic and echocardiographic data might have contributed to distortion of reality. Let us recall how Webster's dictionary defines artifact: "a spurious observation or result arising from preparatory or investigative procedures or any feature that is not naturally present but is a product of an extrinsic agent, method, or the like".

Appetite Depressants↗

PubMed2002

Post-cremation taphonomy and artifact preservation.

Contemporary commercial cremation is a reductive taphonomic process that represents one of the most extreme examples of postmortem human alteration of bone. The thorough reduction and fragmentation of cremated human remains often leaves little biological evidence of diagnostic value. Instead, non-osseous artifacts often provide the best evidence of the origin of the cremated remains, the identity of the decedent, and commingling of the remains of more than one individual. Once human remains have been cremated they are most commonly placed into a processor and reduced into small fragments and fine ash suitable for inurnment or scattering. The type of processor determines the size and utility of the particulates and artifacts available for analysis. The newest type of processors have changed the manner and degree of postmortem bone modification and altered the preservation of diagnostic bone fragments and cremation artifacts. This paper addresses the impact of the newest cremation procedures on forensic analysis of cremated remains.

Forensic Anthropology↗

PubMed1999

[Wavelet application to reduction of stimulus artifact in transient evoked otoacoustic emissions testing].

Otoacoustic emissions(OAEs) are presently considered as an objective clinical test for assessing the integraity of peripheral hearing. Owing to the adding of the reflex waves of the stimuli, recordings of emissions evoked in response to transient stimuli are contaminated by an initial artifact, which inhibits the examination of high frequency cochlear responses that have short latencies. So OAEs testing is of serious limitation in most clinical environments. We propose an artifact reduction technique based on discrete wavelet transform pre-processing method and demonstrate empirically that the method not only improves artifact reduction but also enhances signal-to-noise ratio in the response region.

Acoustic Stimulation↗

PubMed1992

Contribution of rodents to postmortem artifacts of bone and soft tissue.

Postmortem disturbance of human remains by rodents extends beyond production of characteristic tooth mark artifacts in dry bones. Three case examples are presented that demonstrate a spectrum of rodent damage to dry and fresh bone and to fresh and mummified soft tissue. In one case, human remains are used for nesting purposes. Rodents are also noted to be vectors of bone transport. Rodent activities can affect bone recovery, human identification, and interpretation of artifacts to bone and soft tissue. Guidelines to differentiate soft tissue artifacts caused by rodents and carnivores are suggested.

Adult↗

PubMed1990

An algorithm for the suppression of translational motion artifacts in MRI.

The quality of Magnetic Resonance imaging systems has improved to the point that the motion is the most important limitation in many examinations. Gross movements of the patient cause a ghost artifact in the image which can interfere with the diagnosis. In this paper a new method is presented to suppress the translational motion artifact caused by gross movements. The method uses postprocessing on a standard two-dimensional Fourier transform image. It is shown that translational motion causes an additional phase factor in the detected signal and that this phase error can be removed using an iterative algorithm of generalised projections. The method has been tested using computer simulations and successfully removed most of the artifact, even in the presence of noise.

Algorithms↗

PubMed1986

Composition of diesel exhaust with particular reference to particle bound organics including formation of artifacts.

For particulate emissions, standards were established by the US EPA in February 1980. Regulations limiting particulates from new light duty diesel vehicles are valid by model year 1982. The corresponding standards on a pure mass basis do not take into account any chemical character of the diesel particulate matter. Our investigation of the material composition shows that diesel particulates consist mainly of soot (up to 80% by weight) and adsorptively bound organics including polycyclic aromatic hydrocarbons (PAH). The qualitative and quantitative nature of hydrocarbon compounds associated with the particulates is dependent not only on the combustion parameters of the engine but also to an important degree on the sampling conditions when the particulates are collected (dilution ratio, temperature, filter material, sampling time etc.). Various methods for the analyses of PAH and their oxy- and nitro-derivatives are described including sampling, extraction, fractionation and chemical analysis. Quantitative comparison of PAH, nitro-PAH and oxy-PAH from different engines are given. For assessing mutagenicity of particulate matter, short-term biological tests are widely used. These biological tests often need a great amount of particulate matter requiring prolonged filter sampling times. Since it is well known that facile PAH oxidation can take place under the conditions used for sampling and analysis, the question rises if these PAH-derivates found in particle extracts partly or totally are produced during sampling (artifacts). Various results concerning nitro- and oxy-PAH are presented characterizing artifact formation as a minor problem under the conditions of the Federal Test Procedure. But results show that under other sampling conditions, e.g. electrostatic precipitation, higher NO2-concentrations and longer sampling times, artifact formation can become a bigger problem. The more stringent particulate standard of 0.2 g/mi for model years 1986 and 1987 respectively requires particulate trap technology. Preliminary investigations of the efficiency of ceramic filters used reveal that the reduction of the adsorptively bound organics is lower than the decrease of the solid carbonaceous fractions.

Aldehydes↗

PubMedDate not supplied

Artifacts in fundus photographs.

Many artifacts can be found in fundus photography and may be caused by the technician, patient, or camera. Artifacts caused by mechanical problems in the camera or from the patient's media or pupil variations are invisible until the film is developed. Most artifacts, however, can be seen in the viewfinder during the photographic session and can be corrected. When artifactual problems occur, they should be documented in the patient's record, especially if they degrade the quality of the photograph.

Diagnostic Errors↗

PubMed1989

[Technical artifacts in biopsy of the oral cavity. I. Clinical and histopathologic aspects].

In the present work the problems of artifacts introduced in human oral biopsy specimens are discussed. The circumstances that can result in artifacts include: errors by the surgeon or assistant in handling the tissue at the time of biopsy, an improper fixation and faulty tissue processing. Different types of artifacts are described and illustrated and clinical and technical suggestions are given to prevent alterations of normal morphologic and cytologic features that can compromise an accurate diagnosis.

Biopsy↗

PubMed1989

[Optimization of the technic in the study of the upper abdomen using magnetic resonance. I. Artifact reduction].

Complete motion artifact suppression is possible in abdominal MR imaging with the simple optimization of sequence parameters, with no need for special softwares. The authors have studied the influence of sequence parameters modification on the signal/noise relation and on the presence of motion artifacts. The tested parameters included Repetition Time (TR), 150 to 2000 ms, Echo Time (TE), 20 to 120 ms, and the number of acquisitions, 2 to 16. In T1-weighted sequences, the major advantages were offered by the short TR and short TE association, with many acquisitions. Optimal signal/noise relation and complete motion artifact suppression were thus obtained. In T2-weighted sequences, TE values had to be changed according to the desired contrast enhancement, and the number of acquisitions could not be increased to more than 2 in order to keep the acquisition time short.

Abdomen↗

PubMedDate not supplied

Magnetic susceptibility artifacts in gradient-recalled echo MR imaging.

Artifacts related to magnetic susceptibility differences between bone and soft tissue are prevalent on gradient-recalled echo images, particularly when long echo delay times are used. These susceptibility artifacts spatially distort and artifactually enlarge bone contours. This can alter the apparent shape of the spinal canal and exaggerate the degree of spinal stenosis seen in patients with cervical spondylosis. The effects of magnetic susceptibility artifacts in gradient echo imaging were studied in a phantom model and the results were correlated with MR images obtained in patients with cervical spondylosis.

Cervical Vertebrae↗

PubMed1988

Common artifacts encountered in magnetic resonance imaging.

Magnetic resonance imaging has rapidly become a widely accepted and clinically useful imaging modality primarily because of its excellent contrast resolution, ability to perform multiplanar acquisition, and the lack of ionizing radiation. However, the nuances of image acquisition are not trivial. Many technical factors must be considered and understood in order to knowledgeably choose sequence parameters that suppress artifacts and optimize the diagnostic quality of a particular MR examination. Even then, residual artifacts may persist. The presence of the artifacts and their technical basis must be understood before completely accurate MR interpretation can be rendered.

Brain↗