In situ active control of noise in a 4 T MRI scanner

To evaluate the effectiveness of the proposed active noise control (ANC) system for the reduction of the acoustic noise emission generated by a 4 T MRI scanner during operation and to assess the feasibility of developing an ANC device that can be deployed in situ.

Three typical scanning sequences, EPI (echo planar imaging), GEMS (gradient echo multislice), and MDEFT (modified driven equilibrium Fourier transform), were used for evaluating the performance of the ANC system, which was composed of a magnetic compatible headset and a multiple reference feedforward filtered-x least mean square controller.

The greatest reduction, about 55 dB, was achieved at the harmonic at a frequency of 1.3 kHz in the GEMS case. Approximately 21 dB and 30 dBA overall reduction was achieved for GEMS noise across the entire audible frequency range. For the MDEFT sequence, the control system achieved 14 dB and 14 dBA overall reduction in the audible frequency range, while 13 dB and 14 dBA reduction was obtained for the EPI case.

The result is highly encouraging because it shows great potential for treating magnetic resonance imaging noise with an ANC application during real-time scanning.