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Result : Searchterm 'Artifact' found in 62 terms [] and 104 definitions []
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related threadsInfoSheet: - Artifacts - 
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An image artifact is a structure not normally present but visible as a result of a limitation or malfunction in the hardware or software of the MRI device, or in other cases a consequence of environmental influences as heat or humidity or it can be caused by the human body (blood flow, implants etc.). The knowledge of MRI artifacts (brit. artefacts) and noise producing factors is important for continuing maintenance of high image quality. Artifacts may be very noticeable or just a few pixels out of balance but can give confusing artifactual appearances with pathology that may be misdiagnosed.
Changes in patient position, different pulse sequences, metallic artifacts, or other imaging variables can cause image distortions, which can be reduced by the operator; artifacts due to the MR system may require a service engineer.
Many types of artifacts may occur in magnetic resonance imaging. Artifacts in magnetic resonance imaging are typically classified as to their basic principles, e.g.:
Physiologic (motion, flow)
Hardware (electromagnetic spikes, ringing)
Inherent physics (chemical shift, susceptibility, metal)

Several techniques are developed to reduce these artifacts (e.g. respiratory compensation, cardiac gating, eddy current compensation) but sometimes these effects can also be exploited, e.g. for flow measurements.

See also the related poll result: 'Most outages of your scanning system are caused by failure of'
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    • Artifact by Patient Movement
    • Black Boundary Artifact
    • Apodization
    • Aliasing Artifact
    • Apparent Diffusion Coefficient
 
Further Reading:
  Basics:
ARTEFACT VERSUS ARTIFACT
Saturday, 26 January 2002   by www.worldwidewords.org    
Which dental materials conflict with the use of MRI?
Saturday, 29 December 2012   by www.drbicuspid.com    
  News & More:
Clinical examination or whole-body magnetic resonance imaging: the Holy Grail of spondyloarthritis imaging
Tuesday, 28 February 2012   by 7thspace.com    
On the Horizon - Next Generation MRI
Wednesday, 23 October 2013   by thefutureofthings.com    
Technical Assessment of Artifact Production from Neuro Endovascular Coil At 3 Tesla MRI: An In Vitro Study
2012   by www.tmps.or.th    
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Radiology  (4) Open this link in a new windowUltrasound  (60) Open this link in a new window
DC ArtifactInfoSheet: - Artifacts - 
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See Central Point Artifact.

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• View the DATABASE results for 'DC Artifact' (2).Open this link in a new window

 
Further Reading:
  Basics:
Image Artefacts
   by www.fmrib.ox.ac.uk    
MRI Resources 
Raman Spectroscopy - Pacemaker - Artifacts - DICOM - Used and Refurbished MRI Equipment - Jobs
 
Flow ArtifactInfoSheet: - Artifacts - 
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Quick Overview
Please note that there are different common names for this artifact.

Artifact Information
NAME Spin phase effect, flow
DESCRIPTION Vascular ghosts (ghosting artifact), anomalous intensities in images
REASON Movement of body fluids
HELP Flow compensation, presaturation, triggering

Flow effects in MRI produce a range of artifacts, e.g. intravascular signal void by time of flight effects; turbulent dephasing and first echo dephasing, caused by flowing blood.
Through movement of the hydrogen nuclei (e.g. blood flow), there is a location change between the time these nuclei experience a radio frequency pulse and the time the emitted signal is received (because the repetition time is asynchronous with the pulsatile flow).
The blood flow occasionally produces intravascular high signal intensities due to flow related enhancement, even echo rephasing and diastolic pseudogating. The pulsatile laminar flow within vessels often produces a complex multilayered band that usually propagates outside the head in the phase encoded direction. Blood flow artifacts should be considered as a special subgroup of motion artifacts.


Image Guidance
Artifacts can be reduced by reduction of phase shifts with flow compensation (gradient moment nulling), suppression of the blood signal with saturation pulses parallel to the slices, synchronization of the imaging sequence with the heart cycle (cardiac triggering) or can be flipped 90 by swapping the phase//frequency encoding directions.
See also Flow Related Enhancement and Flow Effects.
 
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Further Reading:
  News & More:
MRI measure of blood flow over atherosclerotic plaque may detect dangerous plaque
Friday, 5 April 2013   by www.sciencecodex.com    
Advanced Visualization Techniques Could Change the Paradigm for Diagnosis and Treatment of Heart Disease
Thursday, 31 May 2012   by www.sciencedaily.com    
Searchterm 'Artifact' was also found in the following services: 
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Gibbs ArtifactInfoSheet: - Artifacts - 
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Quick Overview
Please note that there are different common names for this MRI artifact.

Artifact Information
NAME Gibbs, Gibbs ringing, truncation
DESCRIPTION Edge ringing, syrinx-like stripe
REASON Sharp changes in intensity (incomplete digitization of the echo)
HELP More samples

The Gibbs or ringing artifact appears as a series of lines in the MR image parallel to abrupt and intense changes in the object at this location. This artifact does not occur visibly on smooth objects. This artifact is caused by the Gibbs phenomenon, an overshoot or ringing of Fourier series occurring at discontinuities.
In the spinal cord, a small syrinx can be simulated by the Gibbs phenomenon. Gibbs artifacts are also seen in other regions, for example the brain//skull interface.
Fine lines visible in an image may be due to undersampling of the high spatial frequencies, respectively incomplete digitization of the echo.
With more encoding steps the Gibbs artifacts is less intense and narrower. Therefore, e.g. the artifact is more intense in the 256 point dimension of a 256x512 acquisition matrix.


Image Guidance
This problem can only be resolved by smoothing filters (LanczosSigmaFactor, 2-D Exponential Filtering, Gegenbauer Reconstruction etc.) or with a higher acquisition matrix and/or a smaller FOV, to smooth the object.
See also Gibbs Phenomenon and Apodization.
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• View the DATABASE results for 'Gibbs Artifact' (4).Open this link in a new window

 
Further Reading:
  Basics:
Artifacts in MRI
Saturday, 1 October 2011   by www.huc.min-saude.pt    
Lanczos sigma Factor
   by mathworld.wolfram.com    
  News & More:
Troubleshooting the ACR MRI Accreditation Phantom Tests
   by www.aapm.org    
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Metal ArtifactInfoSheet: - Artifacts - 
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Quick Overview

Artifact Information
NAME Metal, susceptibility
DESCRIPTION Signal dropout, bright spots
REASON Field inhomogeneity
HELP Remove the metal

Ferromagnetic metal will cause a magnetic field inhomogeneity, which in turn causes a local signal void, often accompanied by an area of high signal intensity, as well as a distortion of the image. They create their own magnetic field and dramatically alter precession frequencies of protons in the adjacent tissues. Tissues adjacent to ferromagnetic components become influenced by the induced magnetic field of the metal hardware rather than the parent field and, therefore, either fail to precess or do so at a different frequency and hence do not generate useful signal. Two components contribute to susceptibility artifact, induced magnetism in the ferromagnetic component itself and induced magnetism in protons adjacent to the component.
Artifacts from metal may have varied appearances on MRI scans due to different type of metal or configuration of the piece of metal. The biocompatibility of metallic alloys, stainless steel, cobalt chrome and titanium alloy is based on the presence of a constituent element within the alloy that has the ability to form an adherent oxide coating that is stable, chemically inert and hence biocompatible. In relation to imaging titanium alloys are less ferromagnetic than both cobalt and stainless steel, induce less susceptibility artifact and result in less marked image degradation.


Image Guidance
Remove the metal when possible or take a not so sensitive sequence (a SE or another sequence with a rephasing 180 pulse). See also Susceptibility Artifact.
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• View the DATABASE results for 'Metal Artifact' (2).Open this link in a new window

 
Further Reading:
  Basics:
Metal-Induced Artifacts in MRI
   by www.ajronline.org    
Metal Artefact Reduction
Thursday, 9 June 2011   by www.revisemri.com    
MRI Resources 
Used and Refurbished MRI Equipment - Jobs - Open Directory Project - Developers - Shielding - General
 
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