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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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News  (6)  Resources  (10)  Forum  (22)  
 
Susceptibility ArtifactInfoSheet: - Artifacts - 
Case Studies, 
Reduction Index, 
etc.MRI Resource Directory:
 - Artifacts -
 
Quick Overview
Artifact Information
DESCRIPTION
Signal dropout, bright spots, spatial distortion
REASON
HELP
Remove the metal, do not take a gradient echo sequence, take a short echo time
Materials with magnetic susceptibility cause this artifact. There are in general three kinds of materials with magnetic susceptibility: ferromagnetic materials (iron, nickel etc.) with a strong influence and paramagnetic/diamagnetic (aluminium, platinum etc./gold, water, most organic compounds etc.) materials with a minimal/non influence on magnetic fields. In MRI, susceptibility artifacts are caused for example by medical devices in or near the magnetic field or by implants of the patient. These materials with magnetic susceptibility distort the linear magnetic field gradients, which results in bright areas (misregistered signals) and dark areas (no signal) nearby the magnetic material.
mri safety guidance
Image Guidance
Use a spin echo or a fast spin echo sequence, because gradient echo sequences are more sensitve to susceptibility artifacts. A high bandwidth (small water fat shift) and a short echo time help also to reduce this artifact.
In some cases it is even beneficial to use a gradient echo sequence, e.g. a cavernom contains some iron-rich haemosiderin, which also causes a signal void on gradient echo sequences and for this purpose increases the diagnostic image quality.
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• Related Searches:
    • Lung Imaging
    • Magnetic Susceptibility
    • Susceptibility
    • Magnetism
    • Field Strength
 
Further Reading:
  Basics:
MRI Artifact Gallery
   by chickscope.beckman.uiuc.edu    
Susceptibility Artifacts
   by www.mritutor.org    
  News & More:
Metal Artefact Reduction
Thursday, 9 June 2011   by www.revisemri.com    
Ultrashort echo time (UTE) MRI of the spine in thalassaemia
February 2004   by bjr.birjournals.org    
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
Venetian Blind ArtifactInfoSheet: - Artifacts - 
Case Studies, 
Reduction Index, 
etc.MRI Resource Directory:
 - Artifacts -
 
Quick Overview
Artifact Information
NAME
Venetian blind
DESCRIPTION
Loss of signal of flowing blood
REASON
Saturation effect
HELP
Smaller 3D volume, multi chunk, TONE
The saturation effect of inflowing blood in 3D inflow MRA.
mri safety guidance
Image Guidance
Smaller 3D Volume or scans with e.g. tilt optimized nonsaturated excitation. In multi chunk scans TONE decreases this artifact or allows thicker chunks.
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• View the DATABASE results for 'Venetian Blind Artifact' (3).Open this link in a new window

 
Further Reading:
  Basics:
Magnetic Resonance Imaging (MRI)
2003   by www.hull.ac.uk    
MRI Resources 
MRI Physics - MRI Technician and Technologist Schools - Fluorescence - Nerve Stimulator - Coils - Contrast Agents
 
Audio Frequency ArtifactInfoSheet: - Artifacts - 
Case Studies, 
Reduction Index, 
etc.MRI Resource Directory:
 - Artifacts -
 
Quick Overview
Artifact Information
NAME
Audio frequency
DESCRIPTION
Ghosting, lines or spots
REASON
Wrong modulation at audio rate, wrong audio signal
HELP
AC-line synchronization
Two types of audio-frequency problems are possible:
1. Modulation of the MR signal at an audio rate
2. Audio signal component at digitizer input
Problem 1 looks like ghosts, weak copies of the real image, displaced along the phase encoding direction. The number and intensity of the ghosts depends upon the relationship between the period of the audio modulation and the repetition time.
Problem 2 shows up as lines or spots at the appropriate points along the frequency direction. If there is no correlation between the audio period and TR, lines are generated or discrete spots occur.
mri safety guidance
Image Guidance
Both problems can be lessened by use of AC-line synchronization (line trigger).
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Searchterm 'Artifact' was also found in the following services: 
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News  (6)  Resources  (10)  Forum  (22)  
 
Data Clipping (Artifact)InfoSheet: - Artifacts - 
Case Studies, 
Reduction Index, 
etc.MRI Resource Directory:
 - Artifacts -
 
Data clipping artifacts give images a washed-out, non-uniform appearance. If the receiver gain increase, so that the signal level is larger than the maximum ADC value, the reconstructed image brightness was scaled to compensate this. The overall intensity loss as well as the extensive signal is reconstructed outside of the object. This effect is called 'clipping' because on a plot of signal amplitude vs. time, it looks like the top and bottom of the echo has been 'clipped off' with scissors.

See Radio Frequency Overflow Artifact.
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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
Moire Fringes (Artifact)InfoSheet: - Artifacts - 
Case Studies, 
Reduction Index, 
etc.MRI Resource Directory:
 - Artifacts -
 
Quick Overview
Artifact Information
NAME
Moire fringes, moire
DESCRIPTION
Superimposed signals of different phases
REASON
Interferences
HELP
Surface coil, shimming
A moiré pattern is an interference pattern created for example when two grids are overlaid at an angle, or when they have slightly different mesh sizes. The human visual system creates an imaginary pattern of roughly horizontal dark and light bands, the moiré pattern that appears to be superimposed on the lines.
In MRI, the appearance of moiré fringes can be caused by a variety of reasons e.g., inhomogeneity of the main magnetic field caused by a defect shielding (interference with RF pulses), interferences produced by aliasing, and interferences of echoes from different excitation modes (with different echo times).
mri safety guidance
Image Guidance
Take spin echo-based techniques, or a surface coil. This artifact is often sensitive to shimming or susceptibility gradients.
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Further Reading:
  Basics:
MRI Artifact Gallery
   by chickscope.beckman.uiuc.edu    
Moiré pattern
   by en.wikipedia.org    
Moire Fringes
   by www.mritutor.org    
MRI Resources 
Colonography - Blood Flow Imaging - Fluorescence - Sequences - Mobile MRI - Open Directory Project
 
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