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Result : Searchterm 'Noise' found in 12 terms [] and 71 definitions []
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An undesirable background interference or disturbance that affects image quality.
The Noise is commonly characterized by the standard deviation of signal intensity in the image of a uniform object (phantom) in the absence of artifacts. The measured noise may depend on the particular phantom used due to variable effects on the Q of the receiver coil.
Noisy images appear when the SNR-Rate is too low - this is induced by the operator. Image artifacts and RF noise can often be caused by the presence and/or operation of a medical device in the MR environment. There are various noise sources in any electronic system, including Johnson noise, shot noise, thermal noise. Materials produce their own characteristic static magnetic field that can perturb the relationship between position and frequency essential to accurate image reconstruction.
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 medical device that interfere with the proper operation of the MR scanner. Since the MR procedure room is shielded from extraneous RF fields entering the room (Faraday cage), operation of electromagnetically noisy equipment outside the room does not typically affect the MR scanner.
See Signal to Noise Ratio and Radio Frequency Noise Artifact.
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Further Reading:
  Basics:
Image Characteristics and Quality
   by www.sprawls.org    
Brain MR image denoising for Rician noise using pre-smooth non-local means filter
Wednesday, 7 January 2015   by 7thspace.com    
  News & More:
A Neural Mosaic Of Tones
Tuesday, 20 June 2006   by www.sciencedaily.com    
MRI Noise in Utero Not Harmful for Baby's Ears
Tuesday, 28 September 2010   by www.medgadget.com    
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Noise Figure
 
A measure of the noise performance of an amplifier or chain of amplifiers such as a MR receiver. In MR systems the preamplifier should have a very low noise figure to prevent significant degradation of the signal to noise ratio of the MR signal. Noise figure is a ratio in dB's, and is given by: 20 log [Vo/(ViG)] where Vi is the input thermal noise voltage, Vo is the amplifier output noise level and G is the voltage gain of the amplifier (when the input and output impedance's of the amplifier are equal).
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Random Noise
 
Noise whose amplitude follows some probability distribution and is uncorrelated.
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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 2ī10-5 pascal (20 micropascal). Sound level meters contain filters that simulate the earís 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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Further Reading:
  Basics:
MRI Noise in Utero Not Harmful for Baby's Ears
Tuesday, 28 September 2010   by www.medgadget.com    
  News & More:
TOSHIBA SHOWCASES PATIENT-FRIENDLY 3T MR SYSTEM
Sunday, 29 November 2009   by medical.toshiba.com    
Echo Planar Imaging at 4 Tesla With Minimum Acoustic Noise(.pdf)
   by www.bnl.gov    
GE Healthcare unveils Silent Scan MRI for patient comfort
Friday, 25 October 2013   by www.pharmabiz.com    
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Radiology  (15) Open this link in a new windowUltrasound  (15) Open this link in a new window
Gaussian Noise
 
Noise distributed in a normal (Gaussian) pattern. In such a distribution, approximately 65% of all points fall within one standard deviation (s) of the mean.
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Further Reading:
  Basics:
The Rician Distribution of Noisy MRI Data
Monday, 25 February 2008   by www.ncbi.nlm.nih.gov    
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