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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