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.
•
] and 1 definition [
]
Further Reading:
(.pdf)
Random Page
top
