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Research Papers

In Situ Active Noise Cancellation Applied to Magnetic Resonance Imaging

[+] Author and Article Information
Brent W. Rudd, Mingfeng Li

 Vibro-Acoustics and Sound Quality Research Laboratory, School of Dynamic Systems, Mechanical Engineering, 598 Rhodes Hall, P.O. Box 210072, University of Cincinnati, Cincinnati, OH 45221

Teik C. Lim1

 Vibro-Acoustics and Sound Quality Research Laboratory, School of Dynamic Systems, Mechanical Engineering, 598 Rhodes Hall, P.O. Box 210072, University of Cincinnati, Cincinnati, OH 45221teik.lim@uc.edu

Jing-Huei Lee

 School of Energy, Environmental, Biological and Medical Engineering, Center for Imaging Research, Department of Psychiatry, P.O. Box 670583, University of Cincinnati, Cincinnati, OH 45267

1

Corresponding author.

J. Vib. Acoust 134(1), 011017 (Jan 09, 2012) (7 pages) doi:10.1115/1.4005008 History: Received October 04, 2010; Revised June 01, 2011; Published January 09, 2012; Online January 09, 2012

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.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

MRI compatible headphones with outside reference microphone

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Figure 2

Applied FXLMS active noise control system diagram

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Figure 3

Duct example illustrating feedforward control

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Figure 4

Measured transient in situ acoustic noise response of the EPI scan

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Figure 5

Multiple-reference FXLMS active noise control system diagram

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Figure 6

Measured SPL for EPI scan in situ (solid line, Outside Mic; dotted line, Inside Mic)

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Figure 7

Results of (a) EPI scan X gradient power and (b) in situ test results (solid line, Control off; dotted line, Control on)

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Figure 8

Results of (a) EPI scan Y gradient power and (b) in situ test results (solid line, Control off; dotted line, Control on)

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Figure 9

Results of (a) EPI scan Z gradient power and (b) in situ test results (solid line, Control off; dotted line, Control on)

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Figure 10

Results of (a) EPI scan microphone power and (b) in situ test results (solid line, Control off; dotted line, Control on)

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Figure 11

EPI in situ test results for combined response of the microphone and X, Y, Z gradients as references (solid line, Control off; dotted line, Control on)

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