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Result : Searchterm 'Magnetic Field' found in 5 terms [] and 219 definitions []
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Searchterm 'Magnetic Field' was also found in the following services: 
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News  (76)  Resources  (16)  Forum  (18)  
 
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:
    • Magnetism
    • Metal Artifact
    • Susceptibility
    • Spatial Misregistration Artifact
    • Magnetic Susceptibility
 
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 'Magnetic Field' was also found in the following services: 
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Radiology  (9) Open this link in a new windowUltrasound  (2) Open this link in a new window
5 Gauss LimitMRI Resource Directory:
 - Safety -
 
The national regulatory boards decided to limit the threshold for access to MRI areas to 5 gauss.
mri safety guidance
MRI Safety Guidance
It is of special interest for the observer of bureaucratic procedures that the 5 gauss safety limit is ten times higher than the average earth magnetic field, but lower than the magnetic field in electric trains such as subways (up to 7 gauss). For example, the fields measured on the surface of the receiver of a telephone are 35 gauss and of an audio headset 100 gauss.
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• View the DATABASE results for '5 Gauss Limit' (3).Open this link in a new window

 
Further Reading:
  Basics:
Magnetic Sensitivity of MRI Systems to External Iron: The Design Process
   by www.integratedsoft.com    
  News & More:
A Primer on Medical Device Interactions with Magnetic Resonance Imaging Systems
   by govpulse.us    
Modern Implantable Heart Devices Safe For Use In MRI Scans
Wednesday, 16 March 2005   by www.sciencedaily.com    
MRI Resources 
DICOM - Safety Products - Jobs - Databases - Knee MRI - Case Studies
 
Acoustic Noise
 
Vibrations of the gradient coil support structure create sound waves. These are caused by the interactions of the magnetic field created by pulses of the current through the gradient coil with the main magnetic field in a manner similar to a loudspeaker coil. The sounds made by the scanner vary in volume and tone with the type of procedure being performed.
Sound pressure is reported on a logarithmic scale called sound-pressure level, expressed in decibel (dB) referenced to the weakest audible 1 000 Hz sound pressure of 2 * 10-5 pascal (20 micropascal). Sound level meters contain filters that simulate the ear's frequency response. The most commonly used filter provides what is called 'A' weighting, with the letter 'A' appended to the dB units, i.e. dBA.
MRI system noise levels increase with field strength. Disposable earplugs and/or headphones for the patient are recommended in high-field systems. Noise-canceling systems and special earphones are available, and active acoustic control systems were developed, e.g. softtone, pianissimo. A sequence with low noise gradient pulses is also called 'whisper sequence'.

See also Phon and Decibel.
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• View the DATABASE results for 'Acoustic Noise' (9).Open this link in a new window

 
Further Reading:
  Basics:
MRI Noise in Utero Not Harmful for Baby's Ears
Tuesday, 28 September 2010   by www.medgadget.com    
  News & More:
Noise from Magnetic Resonance Imaging Can Have Short-Term Impact on Hearing
Thursday, 22 February 2018   by www.diagnosticimaging.com    
Echo Planar Imaging at 4 Tesla With Minimum Acoustic Noise(.pdf)
   by www.bnl.gov    
TOSHIBA SHOWCASES PATIENT-FRIENDLY 3T MR SYSTEM
Sunday, 29 November 2009   by medical.toshiba.com    
Searchterm 'Magnetic Field' was also found in the following services: 
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News  (76)  Resources  (16)  Forum  (18)  
 
Active Shielding
 
Magnetic shielding through the use of secondary shielding coils designed to produce a magnetic field that cancels the field from primary coils in regions where it is not desired. These coils may be inside the magnet cryostat. Active shielding can be applied to the main magnet or to the gradient magnetic fields.

See also Magnetic Shielding, Self Shielding and Room Shielding.
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• View the DATABASE results for 'Active Shielding' (6).Open this link in a new window

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Radiology  (9) Open this link in a new windowUltrasound  (2) Open this link in a new window
B0
 
[B0] A conventional symbol for the main magnetic field strength (magnetic flux density or induction) in a MRI system. Although historically used, H0 (units of magnetic field strength, ampere//meter) should be distinguished from the more appropriate B0 [units of magnetic induction, tesla].
In current MR systems it has a constant value over time varying from 0.02 to 4 T. Field strengths of 0.5 T and above are generated with superconductive magnets. High field strengths have a better signal to noise ratio (SNR). The optimal imaging field strength for clinical imaging is between 0.5 and 2.0 T.

See also the related poll result: 'In 2010 your scanner will probably work with a field strength of'
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• View the DATABASE results for 'B0' (41).Open this link in a new window

 
Further Reading:
  Basics:
Factors influencing flip angle mapping in MRI: RF pulse shape, slice-select gradients, off-resonance excitation, and B0 inhomogeneities.
Tuesday, 1 August 2006   by www.ncbi.nlm.nih.gov    
Magnetic Field
   by hyperphysics.phy-astr.gsu.edu    
  News & More:
Turbo-FLASH Based Arterial Spin Labeled Perfusion MRI at 7 T
Thursday, 20 June 2013   by www.plosone.org    
Penn researchers to get 7 Tesla whole-body MRI system
Monday, 28 August 2006   by www.eurekalert.org    
Optimizing SPIR and SPAIR fat suppression
Tuesday, 30 November 2004   by clinical.netforum.healthcare.philips.com    
MRI Resources 
Non-English - MRCP - Equipment - Chemistry - Safety Training - MR Guided Interventions
 
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