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Result : Searchterm 'Artifact' found in 62 terms [] and 104 definitions []
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Searchterm 'Artifact' was also found in the following services: 
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Aliasing ArtifactInfoSheet: - Artifacts - 
Case Studies, 
Reduction Index, 
etc.MRI Resource Directory:
 - Artifacts -
 
Quick Overview
Please note that there are different common names for this MRI artifact.
Artifact Information
NAME
Aliasing, backfolding, foldover, phase wrapping, wrap around
DESCRIPTION
Image wrap around
Aliasing is an artifact that occurs in MR images when the scanned body part is larger than field of view (FOV). As a consequence of the acquired k-space frequencies not being sampled densely enough, whereby portions of the object outside of the desired FOV get mapped to an incorrect location inside the FOV. The cyclical property of the Fourier transform fills the missing data of the right side with data from behind the FOV of the left side and vice versa. This is caused by a too small number of samples acquired in, e.g. the frequency encoding direction, therefore the spectrums will overlap, resulting in a replication of the object in the x direction.
Aliasing in the frequency direction can be eliminated by twice as fast sampling of the signal or by applying frequency specific filters to the received signal.
A similar problem occurs in the phase encoding direction, where the phases of signal-bearing tissues outside of the FOV in the y-direction are a replication of the phases that are encoded within the FOV. Phase encoding gradients are scaled for the field of view only, therefore tissues outside the FOV do not get properly phase encoded relative to their actual position and 'wraps' into the opposite side of the image.
mri safety guidance
Image Guidance
Use a larger FOV, RFOV or 3D Volume, apply presaturation pulses to the undesired tissue, adjust the position of the FOV, or select a small coil which will only receive signal from objects inside or near the coil. The number of phase encoding steps must be increased in phase direction, unfortunately resulting in longer scan times.
When this is not possible it can be corrected by oversampling the data. Aliasing is eliminated by Oversampling in frequency direction. No Phase Wrap (Foldover Suppression) options typically correct the phase encoding by doubling the field of view, doubling the number of phase encodes (to keep resolution constant) and halving the number of averages (to keep scan time constant) then discarding the additional data and processing the image within the desired field of view (but this is more time consuming).
Tissue outside this doubled area can be folded nevertheless into the image as phase wrap. In this case combine more than 2 number of excitations / number of signal averages with foldover suppression.
See also Aliasing, Foldover Suppression, Oversampling, and Artifact Reduction - Aliasing.
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• Related Searches:
    • Anti Aliasing
    • Wrap Around Artifact
    • Oversampling
    • Backfolding Artifact
    • Phase Wrapping Artifact
Searchterm 'Artifact' was also found in the following services: 
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Radiology  (4) Open this link in a new windowUltrasound  (60) Open this link in a new window
Foldover ArtifactInfoSheet: - Artifacts - 
Case Studies, 
Reduction Index, 
etc.MRI Resource Directory:
 - Artifacts -
 
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• View the DATABASE results for 'Foldover Artifact' (2).Open this link in a new window

 
Further Reading:
  Basics:
Aliasing or wrap around artifacts
Thursday, 31 March 2011   by de.slideshare.net    
MRI Resources 
Services and Supplies - Patient Information - Open Directory Project - Collections - Bioinformatics - Chemistry
 
Ghosting ArtifactInfoSheet: - Artifacts - 
Case Studies, 
Reduction Index, 
etc.MRI Resource Directory:
 - Artifacts -
 
Quick Overview
Artifact Information
NAME
Ghosting, ghost
DESCRIPTION
Displaced reduplications of image in phase encoding direction
REASON
Motion, heartbeat, respiration
HELP
Triggering, breath hold, pharmaceuticals to reduce bowel motion
Ghosting artifacts are in the most cases caused by movements (e.g., respiratory motion, bowel motion, arterial pulsations, swallowing, and heartbeat) and appear in the phase encoding direction.
mri safety guidance
Image Guidance
Ghosting artifacts can be reduced by respiratory and cardiac triggering, the use of breath holding pulse sequences, flow compensation or presaturation pulses, depending on their origin. To reduce bowel motion also pharmaceuticals, such as glucagon or scopolamine are useful. This will decrease artifacts from both peristalsis and breathing.

See also Motion Artifact, Phase Encoded Motion Artifact, Cardiac Motion Artifact, and Artifact Reduction - Motion.
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• View the DATABASE results for 'Ghosting Artifact' (5).Open this link in a new window

 
Further Reading:
  Basics:
MRI Artifact Gallery
   by chickscope.beckman.uiuc.edu    
Searchterm 'Artifact' was also found in the following services: 
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News  (6)  Resources  (10)  Forum  (22)  
 
DC Offset ArtifactInfoSheet: - Artifacts - 
Case Studies, 
Reduction Index, 
etc.MRI Resource Directory:
 - Artifacts -
 
This artifact looks like a pixel at the exact center, which is brighter or darker than the surroundings by the Fourier transformation of a constant raw data offset.

See Central Point Artifact.
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Further Reading:
  Basics:
Image Artefacts
   by www.fmrib.ox.ac.uk    
Searchterm 'Artifact' was also found in the following services: 
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Radiology  (4) Open this link in a new windowUltrasound  (60) Open this link in a new window
Staircase ArtifactInfoSheet: - Artifacts - 
Case Studies, 
Reduction Index, 
etc.MRI Resource Directory:
 - Artifacts -
 
Quick Overview
Artifact Information
NAME
Staircase
DESCRIPTION
Staircase like nuance
REASON
Slices too thick, no overlapping
HELP
Overlapping slices
Staircase artifacts might be seen in projection of the slice thickness in case of MIP or MPR reconstructions.
mri safety guidance
Image Guidance
Use overlapping slices to reduce this artifact by changing the slice gap to a negative value. In most cases, a negative value of 20-30% is sufficient.
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• View the DATABASE results for 'Staircase Artifact' (2).Open this link in a new window

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