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Result : Searchterm 'Interference' found in 2 terms [] and 12 definitions []
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InterferenceForum -
related threadsInfoSheet: - Artifacts - 
Case Studies, 
Reduction Index, 
etc.
 
See Radio Frequency Noise Artifact.
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Constructive Interference Steady StateInfoSheet: - Sequences - 
Intro, 
Overview, 
Types of, 
etc.
 
(CISS) This gradient echo sequence is a stimulated T2 echo. Two TrueFISP sequences are acquired with differing RF pulses and than combined for strong T2 Weighted high resolution 3D images.
These TrueFISP sequences are normally affected by dark phase dispersion bands, which are caused by patient induced local field inhomogeneities and made prominent by the relatively long TR used. The different excitation pulse regimes offset these bands in the 2 sequences. Combining the images results in a picture free of banding. The image combination is performed automatically after data collection, adding some time to the reconstruction process. The advantage of the 3D CISS sequence is its combination of high signal levels and extremely high spatial resolution.
Used for, e.g. inner ear, cranial nerves and cerebellum.
See also Steady State Free Precession.

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Further Reading:
  News & More:
Pediatric and Adult Cochlear Implantation1
2003   by radiographics.rsnajnls.org    
MRI Resources 
Open Directory Project - Musculoskeletal and Joint MRI - Artifacts - Functional MRI - MRA - Implant and Prosthesis
 
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 moire 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).


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    
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Radio Frequency Noise ArtifactInfoSheet: - Artifacts - 
Case Studies, 
Reduction Index, 
etc.MRI Resource Directory:
 - Artifacts -
 
Quick Overview
Please note that there are different common names for this artifact.

Artifact Information
NAME Radio frequency noise, interference, crisscross / Herringbone artifact
DESCRIPTION Static on the image
REASON Electromagnetic emissions
HELP Shielding, eliminate the factor of disturbance

RF noise, which often appears as static on the image, can be caused by a medical device located anywhere in the MR procedure room. RF noise is a result of excessive electromagnetic emissions from the device that interference with the proper operation of the MR scanner. The interference is attenuated and aliased in the frequency direction.


Image Guidance
In the first case try to eliminate the factor of disturbance, if the problem persists screen the magnet- and room shielding. See also Signal to Noise Ratio.
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Further Reading:
  Basics:
MRI Artifact Gallery
   by chickscope.beckman.uiuc.edu    
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Crosstalk (Artifact)InfoSheet: - Artifacts - 
Case Studies, 
Reduction Index, 
etc.MRI Resource Directory:
 - Artifacts -
 
Quick Overview

Artifact Information
NAME Crosstalk, cross excitation
DESCRIPTION Anomalous intensities in an image
REASON Interference
HELP Slice gap minimum 10%

Crosstalk is an artifact introduced into images by interference between adjacent slices of a scan, caused by a slice profile that is not ideal due to the constraints of the measurement technology. If the slice distances are too small, there is cross talk between the slices, which can affect T1 contrast.


Image Guidance
This artifact can be eliminated by limiting the minimum spacing (for the most sequences a minimum gap 10% and for IR sequences 20%) between the slices. Crosstalk can also be reduced by selection of interleaved slices (so a slice gap will not be necessary), but interleaved data acquisition can produce large mean intensity differences between adjacent slices.

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Further Reading:
  Basics:
MRI GLOSSARY
   by fonar.com    
Slice-overlap Artifacts
   by www.mritutor.org    
MRI Resources 
Safety Training - MRI Technician and Technologist Schools - Pacemaker - Contrast Enhanced MRI - Online Books - MRI Centers
 
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