Experimental Study of Active Acoustic Noise Control in a 4T MRI Scanner In-Situ

Introduction The acoustic noise generated from the MRI system is a serious safety concern as well as a technical challenge for MR and acoustic noise control scientists. The emitted high noise levels can be both annoying and harmful to patients and healthcare workers, especially after long term exposure. Although various passive methods have been proposed to deal with this problem, active noise control (ANC) has attracted much attention in recent years. In our prior study [1, 2], we demonstrated noise reduction in a simulated MRI environment with MRI compatible headphones and microphones. Here, we report noise reduction achieved using our ANC system during scanning at the MRI in-situ. Methods and Results A 4T Varian UnityINOVA whole-body MRI scanner, operated using EPI pulse sequences, was utilized in this study. A dummy was outfitted with a pair of MRI compatible headphones containing piezoceramic speakers with optical microphones installed in the earpiece, shown in Figure 1. A controller was implemented using a laptop computer equipped with a dSPACE system. The multi-channel device also has anti-aliasing and reconstruction filters. First, the sound pressure level (SPL) at the patient ear locations was measured during EPI scanning without the ANC system activated. Then the scanning was repeated with the ANC system operational and the measured SPL compared to the original data. The control system [3], shown in Figure 2, has a secondary path model, S(z), representing the speaker-microphone system. The transfer function,