Abstract
Magnetic resonance imaging (MRI) machine generates a noise which reaches 140dB at maximum level during a medical examination. The purpose of this paper is to control a MRI noise which transmitted from the scanning room by using active noise control (ANC) system with the piezoelectric (PZT) speaker. In the model experiments, semi-anechoic room is used to substitute for the MRI scanning room. The attenuation levels by the ANC system were measured, which using 1/1 octave pure tones of 125 - 4000Hz and the dummy MRI noise. In order to estimate the control effect, the distributions of equivalent sound pressure level around the door were measured by the line scanning microphone. The experimental results show that the transmission noise was attributable mainly to the leak noise from door, and the noise reductions at control microphone were obtained about 14dB by using the present ANC system. However, these reductions were only obtained at the near-field of control microphone, the transmission noise in entire field of the room could not be reduced.
