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At least 577 records · Page 32Linked to original sources
PubMed1988

Motion artifact reduction in MR imaging of the abdomen: gradient moment nulling versus respiratory-sorted phase encoding.

Two currently available methods of reducing motion-induced artifact on magnetic resonance (MR) images, respiratory-sorted phase encoding (RSPE) and gradient moment nulling (GMN), were compared in images of the upper abdomen obtained with long repetition and long echo times. For ten subjects, two series of axial MR images were obtained with identical parameters except that RSPE was used in one and GMN in the other. Images were evaluated by three independent radiologists, and region-of-interest measurements were obtained to calculate signal-difference-to-noise ratios (SD/Ns) for liver versus gallbladder and liver versus the right kidney. Maximum ghost intensity and the standard deviation of motion-induced noise were also calculated. GMN was superior to RSPE for motion artifact reduction in all ten cases. The SD/N for liver versus both gallbladder and right kidney was significantly higher with GMN. Presaturation pulses applied outside the volume of interest reduced aortic and inferior vena cava signal and virtually eliminated artifact from these vessels but did not noticeably affect signal from intrahepatic vessels. GMN combined with presaturation pulses is a highly effective method of motion artifact reduction in the upper abdomen.

Abdomen↗
PubMed1990

Metallic ballistic fragments: MR imaging safety and artifacts.

The ferromagnetism of various bullets and shotgun pellets was tested in vitro. Magnetic deflection showed that four of 21 metallic specimens tested (all bullets) demonstrated marked ferromagnetism. Three of these four were made outside the United States; two of the four were known to contain steel, and the other two were reportedly either copper or copper-nickel-jacketed lead bullets (indicating that the ferromagnetism was due to impurities in the bullet jackets or cores). Ferromagnetic bullets readily rotated within a gelatin phantom in response to magnetic torque. Nonferromagnetic bullets and pellets demonstrated only mild to moderate metal artifact during spin-echo and gradient-echo magnetic resonance (MR) imaging. However, all four of the ferromagnetic bullets produced severe MR artifacts and image distortion. MR studies of seven patients with retained bullets, pellets, or shrapnel were reviewed. In six of the seven, only mild MR artifacts were seen. Only intracranial shrapnel (presumably steel) in one patient created significant artifact. All seven patients with retained bullets and shotgun pellets were imaged safely with MR. However, caution should be exercised with MR imaging in the presence of metallic foreign bodies, particularly if they are located near vital neural, vascular, or soft-tissue structures.

Adolescent↗
PubMed1990

Comet-tail artifact from cholesterol crystals: observations in the postlithotripsy gallbladder and an in vitro model.

The "comet tail" is a well-known ultrasound artifact that appears as a series of parallel bands radiating from a source. This artifact was observed in the gallbladder lumen in eight of 10 patients after extracorporeal shock wave lithotripsy of radiolucent calculi. To investigate the cause of the comet tail artifact, cholesterol crystals were studied in an in vitro model. The comet-tail appearance was reproduced in vitro and was found to be directly related to the interrogating frequency and the size of the crystal aggregates. The authors conclude that cholesterol crystals can serve as the source of the comet-tail artifact secondary to reverberation within the crystals.

Cholelithiasis↗
PubMed1986

The V-shaped artifact of the gallbladder wall.

Among 20,000 patients who had undergone abdominal or gallbladder sonographic examinations, 36 had a short V-shaped artifact originating from an hyperechoic focus in the gallbladder wall. Associated symptoms were varied and nonspecific. The 10 gallbladders excised because of associated cholelithiasis showed a thickened wall, and seven patients had diverticulosis of the wall with impacted stones. In vitro sonographic examination of five gallbladders reproduced the "V" artifact and showed that it originated from a small intramural cholesterol stone. The V artifact should be distinguished from the larger comet-tail and ring-down artifacts, which arise from metal or gas.

Adult↗
PubMed1991

Sonographic artifacts and their origins.

Artifacts are encountered daily in clinical sonography. They may be observed in B-mode gray-scale imaging, spectral pulsed Doppler imaging, and color Doppler imaging. Most of these distortions can be understood at a basic level by an appreciation of the form of the focused sound beam, the interaction of sound with tissue, and assumptions made about the spatial assignment of reflected echoes. Sonographic systems assign depth based on the time interval of round-trip echo travel and assume a straight line and singular path from transducer to reflector and reflector to transducer. The same speed of sound is assumed in all tissues for the purposes of spatial assignment. Some inherent acoustic artifacts are used reflexively to characterize tissue. Strong acoustic enhancement behind an anechoic structure confirms the diagnosis of a cyst. Clean acoustic shadowing distal to an echogenic focus in the gallbladder leads us to the diagnosis of gallstones. If unrecognized, acoustic artifacts can cause serious misdiagnoses. Several commonly encountered artifacts are illustrated, with a basic physical explanation of their occurrence.

Humans↗
PubMed1991

Motion artifact simulating aortic dissection on CT.

We recently imaged two patients clinically suspected of having aortic dissection whose contrast-enhanced CT examinations, obtained on a new scanner with a 1-sec scanning time, showed findings suggesting an ascending aortic dissection. The subsequent clinical course and evaluation implied that the CT findings were predominantly artifactual. We identified identical artifacts in 18% of 50 consecutive contrast-enhanced CT examinations performed for a variety of indications on the same scanner. The double-lumen artifact, simulating an intimal flap, occurs in the proximal ascending aorta and is limited to one or two contiguous transaxial images. The artifact was not detected on two other CT units. We believe the artifact arises from motion of the aortic wall and the surrounding pericardial recesses during image acquisition.

Adult↗
PubMedDate not supplied

Determination of the temperature artifact during ultrasound hyperthermia.

Temperature artifacts produced by very small uncoated thermocouples during ultrasonic heating are evaluated by backward extrapolation of the linear portion of the temperature rise curve or by backward extrapolation of the exponential portion of the temperature decay curve. The accuracy of these techniques for larger clinically used thermocouples is investigated by use of a two-dimensional model of the bioheat equation which simulates the transfer of heat radially from a probe 1 mm in diameter. The accuracy of these techniques is found to depend upon the perfusion rate. In the absence of perfusion, both extrapolation techniques underestimate the artifact by nearly 40%. Extrapolation of the temperature rise curve is very sensitive to the perfusion rate and this technique results in errors exceeding 100% when the perfusion rate is high. Extrapolation of the temperature decay curve produces more consistent results. Over a blood flow range of 0-100 ml/100 g per min, the artifact is underestimated by an amount that varies from approximately 40% to 30% respectively. Thus, the artifact can be determined to within 5% by this technique by increasing the extrapolated value by 35%.

Blood Flow Velocity↗
PubMedDate not supplied

Temperature artifacts produced by thermocouples used in conjunction with 1 and 3 MHz ultrasound.

The relative temperature artifacts produced by a selection of commercially available thermocouples and catheters were evaluated in radiation bolus and beef phantoms heated by 1 and 3 MHz continuous ultrasound. The thermocouples included a 23 gauge needle microprobe inserted directly into the phantoms, polyurethane-sheathed, Teflon-sheathed, and exposed-tip thermocouples, each inserted into a 19 gauge polyurethane closed-end catheter, a multisensor Teflon-sheathed probe inserted into a 16 gauge polyurethane catheter and a Teflon-sheathed single-sensor probe without a catheter. The needle microprobe and the polyurethane-sheathed thermocouple produce equivalent artifacts. The artifacts produced by the Teflon and exposed-tip thermocouples are 1.4 +/- 0.3 times greater, that produced by the multisensor Teflon-sheathed probe is 2.1 +/- 0.3 times greater, and that produced by the Teflon-sheathed thermocouple without a catheter is 2.3 +/- 0.4 times greater. The results in the beef phantom indicate that the needle microprobe and polyurethane-sheathed thermocouple both produce artifacts of 0.7 +/- 0.1 degree in tissue at an SAR of 100 W/kg.

Body Temperature↗
PubMed1983

Experimental artifacts and the analysis of ligand binding data: results of a computer simulation.

Use of computerized analysis techniques for ligand binding data have recently become generally available, and are now used quite routinely. When used appropriately, these tools can improve the precision of the estimated parameters for binding affinity, K, and capacity, R. Furthermore, such programs can also calculate the uncertainty of the estimates e.g., as a percent coefficient of variation (%CV). However, because of unmeasured variability in specific activity, tracer purity, counting efficiency, counter background, efficiency of separation, etc., the actual uncertainty in the parameters K and R is usually much larger than stated. In an attempt to examine the effects of such artifacts, we have developed a computer program which simulates data arising from a number of commonly used experimental designs, and then intentionally distorted with each of these artifacts. Finally, the data are converted to B/F and B and plotted in the conventional Scatchard plot. Distortions revealed in this graph are indicative of the effect each artifact has on the parameter estimates. The computer program is generally written to stimulate the binding of 2 or more ligands to one, two or many classes of independent or cooperative specific sites as well as to nonspecific sites. Thus, the program is applicable in a wide variety of situations. Results show that low tracer purity ("bindability") or low filtration efficiency will significantly alter the measured R value. Poorly determined specific radioactivity may significantly alter the measured K value as well. Imprecise measurement of machine background may result in the spacious appearance of positive cooperativity, or of additional high or low affinity classes of binding sites. Finally, under some circumstances, it is possible to detect and correct for the presence of these artifacts.

Computers↗
PubMed2001

Efficient visual search by category: specifying the features that mark the difference between artifacts and animals in preattentive vision.

In this report, we explored the features that support visual search for broadly inclusive natural categories. We used a paradigm in which subjects searched for a randomly selected target from one category (e.g., one of 32 line drawings of artifacts or animals in displays ranging from three to nine items) among a mixed set of distractors from the other. We found that search was surprisingly fast. Target-present slopes for animal targets among artifacts ranged from 10.8 to 16.0 msec/item, and slopes for artifact targets ranged from 5.5 to 6.2 msec/item. Experiments 2-5 tested factors that affect both the speed of the search and the search asymmetry favoring detection of artifacts among animals. They converge on the conclusion that target-distractor differences in global contour shape (e.g., rectilinearity/curvilinearity) and visual typicality of parts and form facilitate search by category. We argue that existing theories are helpful in understanding these findings but that they need to be supplemented to account for the specific features that specify categories and to account for subjects' ability to quickly locate targets representing heterogeneous and formally complex categories.

Adult↗
PubMed1986

Artifacts in ultrasound imaging.

Ultrasound imaging artifacts of acoustic origin relating to resolution, propagation path, and attenuation are reviewed. Lateral and axial resolution limitations are artifactual in nature since a failure to resolve means a loss of detail and two adjacent structures may be visualized as one. Apparent resolution close to the transducer (speckle) is not directly related to tissue texture but is a result of interference effects from the distribution of scatterers in the tissue. Reverberation produces a set of equally spaced artifactual echoes distal to the real reflectors. The mirror image artifact is the presentation of objects that are present on one side of a strong reflector, appearing on the other side as well. Shadowing and enhancement are useful artifacts for determining the nature of masses. Enhancement results from low attenuation objects in the sound path while shadowing results from strongly reflecting or strongly attenuating objects. Additional artifacts include section thickness, refraction, multipath, side lobe, grating lobe, focal enhancement, comet tail, ring down, speed error, and range ambiguity.

Diagnostic Errors↗
PubMedDate not supplied

Digital subtraction method for transient evoked otoacoustic emission recording with ipsilateral noise suppression: an application to stimulus artifact reduction.

The suppression of transient evoked otoacoustic emissions (TEOAEs) by continuous ipsilateral noise masking was investigated to explore the feasibility of its use in the elimination of the acoustical stimulus artifact. A reference noise template was obtained by stimulating the ear with identically reproducible digitally synthesized broadband noise. The same noise was used to suppress a TEOAE generated by an ipsilaterally presented click under the same conditions. Digital subtraction of the reference noise from the noise-suppressed TEOAE resulted in obtaining a template of a click artifact for that ear. The results have shown that the digital subtraction method cancels the suppressor noise, enabling the observation of the suppressed TEOAE. The subtraction of the stimulus artifact template from the original TEOAE allowed the recovery of the emission waveform with substantially reduced stimulus artifact, thus enabling the recovery of high-frequency otoacoustic emission components.

Acoustic Stimulation↗
PubMed1975

A fully automatic device for compensating for artifacts in conventional catheter-manometer pressure recordings.

A device is described which detects the resonant artifacts in clinical cathetermanometer systems and automatically sets a notch filter so as to provide some measure of compensation. The equalised response characteristic does visibly improve transient response by removing resonant artifacts due to the uneven transfer function characteristic in these systems. Artifacts due to knocking of the catheter by the heart, external vibrations induced in the manometer, its mechanical support, or the catheter are reduced, but not eliminated. Nevertheless, the system described here has provided a solution to an important class of artifacts in conventional fluid filled catheter-manometer pressure recordings.

Automation↗
PubMed2002

[The study of the MRI artifacts caused by keepers].

OBJECTIVE: The aim of this research was to observe the extension of MRI artifacts caused by keepers. METHODS: Five samples were imaged in a water phantom and a living human subject by 0.15 Tesla magnetic resonance devices. The maximum diameters of artifacts were measured and compared. RESULTS: The maximal diameters of the artifacts caused by disc-shaped and post-shaped keepers were 95.5mm and 139.4mm. CONCLUSION: Compared with the post-type keeper, the artifacts caused by disc-type keepers diminished significantly, and the difference of the maximal diameter reached statistical significance.

English Abstract↗
PubMed2001

[MRI artifacts caused by keepers in a dental arch].

OBJECTIVE: This research was designed to observe the degree of artifacts caused by 1-4 keepers. METHODS: Samples were imaged in a living human subject by 0.15 Tesla MR devices in sagital plane. Results were analyzed and the maximal diameters of artifacts were measured. RESULTS: The maximal diameters of the artifacts caused by 1-4 keepers were 101-109.6mm. CONCLUSION: Even with four keepers in the dental arch, the degree of artifact is still limited.

English Abstract↗
PubMedDate not supplied

MR of ballistic materials: imaging artifacts and potential hazards.

The most common ballistic materials available in the urban setting were studied for their MR effects on deflection force, rotation, heating, and imaging artifacts at 1.5 T to determine the potential efficacy and safety for imaging patients with ballistic injuries. The 28 missiles tested covered the range of bullet types and materials suggested by the Cleveland Police Department. The deflection force was measured by the New method. Rotation was evaluated 30 min after bullets had been placed in a 10% (weight per weight) ballistic gelatin designed to simulate brain tissue, with the long axis of the bullet placed parallel and perpendicular to the Z axis of the magnet. Heating was measured with alcohol thermometers by imaging for 1 hr alternatively with gradient-echo and spin-echo sequences (RF absorption = 0.033 and 0.326 w/kg respectively). Image artifacts on routine sequences were evaluated. All the steel-containing bullets except for the Winchester armor-piercing 38 caliber exhibited deflection. A nonsteel 7.38-mm Mauser also deflected. Deflection range was 514 to 15,504 dynes. Rotation occurred when the bullets were not parallel to the Z axis. Temperature changes were not significant. Deflecting projectiles resulted in obliteration of the image. The artifacts from other projectiles were small but varied by content. The artifact of the Winchester armor-piercing 38-caliber bullet was similar to those without steel. Bullets that contain steel or ferromagnetic contaminates such as nickel can be rotated within the MR unit.(ABSTRACT TRUNCATED AT 250 WORDS)

Firearms↗
PubMed1990

Sponge artifact in biopsy specimens.

We describe a sponge-induced artifact in histologic sections of small biopsy specimens. The artifacts are angulated, often triangular holes within the tissue. They appear to be introduced as individual sponge barbs become embedded in the perimeter of biopsy specimens during tissue processing. The artifact is generally of little importance, but in certain specimens, such as needle biopsies of the kidney or liver, it may occasionally obscure important information. Other methods, such as lens paper wrapping, may be superior in these situations. The utility of the tissue cassette sponge, in most situations, outweighs the artifact.

Biopsy↗
PubMed1990

Signal alterations, artifacts and image distortion induced by a superparamagnetic contrast medium. A phantom study in a 0.3 tesla MR system.

In a phantom study using a 0.3 tesla MR system the signal alterations, artifacts and image distortion induced by a bowel contrast medium containing superparamagnetic magnetite particles were evaluated. A concentration of 20 mg iron/l was most useful because it caused a significant signal reduction without disturbing artifacts and image distortion. The signal reduction was most pronounced on long TR/TE spin echo sequences. The appearance and distribution of artifacts are related to the direction of the static magnetic field and frequency encoding gradient. The size of artifacts is related to the concentration of the contrast medium and the band width used.

Contrast Media↗