Active noise control using remotely placed sources: Application to magnetic resonance imaging noise and equivalence to the time reversal inverse filter

Abstract

This paper explores the feasibility of active control of noise from magnetic resonance imaging (MRI) systems using control sources placed outside of the region that MRI scanners are sensitive to ferrous materials. Active noise control (ANC) is shown here to be equivalent to the time reversal (TR) inverse filter technique with a 180° phase shift. Since TR is capable of remotely focusing sound energy to a point in space, it follows that ANC may also be remotely focused. This paper explores the remote delivery of a noise-canceling signal to a desired location (e.g. a patient’s ears). A parameterization study testing frequency dependence and signal length is conducted to determine the effectiveness of the remote delivery. The reduction of MRI noise using ANC is demonstrated using recordings of MRI noise. The parameterization and MRI noise reduction studies are conducted in a reverberation chamber and in a laboratory room with a lower reverberation time. Frequencies below 1 kHz and narrowband signals are easier to control, with reductions up to 20 dB. MRI noise is reduced by up to 18 dB in overall sound pressure level. These results utilized a single control loudspeaker; further reductions should be possible with multiple control sources.