In situ active noise cancellation applied to magnetic resonance imaging

Magnetic Resonance Imaging (MRI) is a powerful medical diagnostic tool. Unfortunately, the loud sound produced during scanning is unpleasant, potentially harmful to patients, and may limit imaging protocol. Previously, a variety of approaches have been proposed to reduce noise exposure with limited success. This work is directed at the application of an active noise control system which generates a secondary sound signal fed into a set of headphones that could be worn by the patient. To this end, prior studies have been conducted in a sound quality chamber to aid in the development and implementation of the hardware, algorithms and procedures, which resulted in an active noise cancellation system tailored to conditions present during MRI. This system performs well during physical simulation of scanning conditions. In this study, the headphones are worn by a dummy during in situ MRI scanning. Our specific effort is to take a selected set of successful experiments under simulated conditions and repeat it during live scanning to evaluate the real time performance of the system conducted in situ. The evaluation was conducted with an echo planar imaging (EPI) scanning sequence and the procedure adjusted to maximize the performance of the system. The sound pressure levels at the patient's ear were measured with and without active control operational, and the results were compared to evaluate the active noise cancellation system's performance during live scans. The controller produced an overall reduction of 10.6 dBA across the full audible spectrum.