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Radio FrequencyForum -
related threads
 
(RF) Radio frequency refers to that portion of the electromagnetic spectrum in which electromagnetic waves can be generated by alternating current fed to an antenna.
The RF pulses used in MRI are commonly in the 1-100 megahertz range, and their effect upon a body is potential heating of tissues and foreign bodies, such as metallic implants, mainly at the surface.
This is a principal area of concern for MRI safety limits caused by absorption (see specific absorption rate) of the applied pulses of RF energy.


Image Guidance
The higher the frequency, the larger will be the amount of heat developed.
The more ionic the biochemical environment in the tissue, the more energy that will be deposited as heat.
This effect is well known for homogeneous model systems, but the complex structure of various human tissues makes detailed theoretical calculations very difficult, if not impossible. By scanning problems, it is important to verify the transmission frequency. If the RF transmitted into the patient was, e.g. 5000 Hz lower than the resonance frequency of the protons, no protons was excited, and no signal returns.
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Further Reading:
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Radio frequency
   by en.wikipedia.org    
  News & More:
On the estimation of the worst-case implant-induced RF-heating in multi-channel MRI.
Thursday, 2 March 2017   by www.ncbi.nlm.nih.gov    
Numerical investigations of MRI RF field induced heating for external fixation devices
Thursday, 7 February 2013   by 7thspace.com    
Safety and reliability of Radio Frequency Identification Devices in Magnetic Resonance Imaging and Computed Tomography
Thursday, 4 February 2010   by 7thspace.com    
Radiologists Offer Non-surgical Treatment For Early-stage Liver Cancer
Saturday, 5 March 2005   by www.sciencedaily.com    
MRI Resources 
Crystallography - Spectroscopy - Corporations - Services and Supplies - Bioinformatics - Jobs pool
 
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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• View the DATABASE results for 'Radio Frequency Noise Artifact' (3).Open this link in a new window

 
Further Reading:
  Basics:
MRI Artifact Gallery
   by chickscope.beckman.uiuc.edu    
MRI Resources 
Abdominal Imaging - Brain MRI - Breast MRI - Knee MRI - Nerve Stimulator - Libraries
 
Radio Frequency Overflow 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 overflow, data clipping
DESCRIPTION Image non-uniform
REASON Signal too intense
HELP Manually decrease of the receiver gain

The received radio frequency signal is too strong, parts of the signal get lost by converting from analog to digital, resulting in a washed out image.


Image Guidance
Auto-prescanning usually adjusts the amplification at the receiver in a way, that the received signal could be processed without any loss. Else the receiver gain must be corrected manually.
See also Data Clipping Artifact, Artifact Overview and Artifacts Reduction Index.
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• View the DATABASE results for 'Radio Frequency Overflow Artifact' (2).Open this link in a new window

 
Further Reading:
  Basics:
RF Overflow Artifacts
   by www.mritutor.org    
  News & More:
Magnetic Resonance Imaging (MRI)
2003   by www.hull.ac.uk    
Searchterm 'Image Guidance' was also found in the following service: 
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Radio Frequency Quadrature ArtifactInfoSheet: - Artifacts - 
Case Studies, 
Reduction Index, 
etc.MRI Resource Directory:
 - Artifacts -
 
Quick Overview
Artifact Information
NAME Radio frequency quadrature
DESCRIPTION Bright spot in the center of the image, ghosting
REASON RF detection circuitry problem
HELP Call the service

Radio frequency quadrature artifacts occur when the detector channels of the quadrature detector are disturbed.
A DC offset of one amplifier output can e.g., produce a bright point in the center of the field of view (see also central point artifact), or a higher gain of one detector channel can generate diagonally ghosting.


Image Guidance
Radio frequency quadrature artifacts are technical faults and must be eliminated by the service.
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Further Reading:
  News & More:
Magnetic Resonance Imaging (MRI)
2003   by www.hull.ac.uk    
MRI Resources 
Open Directory Project - Cardiovascular Imaging - Chemistry - Veterinary MRI - Musculoskeletal and Joint MRI - Mobile MRI
 
Receiver turn on ArtifactInfoSheet: - Artifacts - 
Case Studies, 
Reduction Index, 
etc.MRI Resource Directory:
 - Artifacts -
 
Quick Overview

Artifact Information
NAME Receiver turn on
DESCRIPTION Line across the center of the image
REASON Combination of problems
HELP Call the service

A receiver turn on artifact (not a true MR signal) appears similarly like a FID signal artifact, except that they extend into the signal-free region, while the FID (a real MR signal) is confined to the projection of the sample along the readout axis.


Image Guidance
FID artifacts cannot occur on gradient echo images, but receiver turn on is still possible on gradient echoes.
See also FID Signal Artifact.
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Further Reading:
  Basics:
MRI Artifact Gallery
   by chickscope.beckman.uiuc.edu    
MRI Resources 
Software - Homepages - DICOM - Process Analysis - Anatomy - Abdominal Imaging
 
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