Magnetic Resonance Imaging, Vol. 15, No. 7, pp. 815-822, 1997 0 1997 Elsevier Science Inc. All rights reserved. Printed in the USA. 0730-725x/97 $17.00 + .OO ELSEVIER 0 Original Contribution PI1 SO730-725X(97)00090-8 ANALYSIS OF ACOUSTIC NOISE IN MRI Z.H. CHO,*? S.H. PARK,-/- J.H. Km&t S.C. CHuiw,t S.T. CHuNci,t J.Y. CHUNG,~ C.W. MOON,+ J.H. YI,$ C.H. SIN,§ AND E.K. WONG* *Department of Radiological Sciences, University of California, Irvine, CA 92679, TDepartment of Electrical Sciences, Korea Advanced Institute of Science & Technology Cheongyangni, Seoul, Korea, $Medical Electronics Team, Samsung Advanced Institute of Technology, Suwon. Korea, SDepartment of Diagnostic Imaging, Samsung Medical Center, Seoul, Korea Acoustic or sound noise due to gradient pulsing has been one of the problems in magnetic resonance imaging (MRI), both in patient scanning as well as in many areas of psychiatric and neuroscience research such as functional MRI. Our recent observations in functional MRI for the visual and motor cortex show very different results with sound noise in comparison with the results obtained without sound noise. Although a number of ideas have been suggested in the literature about the possible elimination or reduction of sound noise, progress has been slow due to the basic role of gradient pulsing in MR imaging. Before we tackle the sound-noise-reduction problem, we believe that a systematic study of sound or acoustic noise behavior will provide important information for future endeavors in this area of research in MRI systems, in both commercial and research systems. Therefore, we report on some typical behavior of sound noise observed from MRI scanners and the analyses of their characteristics. Data are obtained both from a commercial MRI scanner (GE Signa 1.5-T EPI system) as well as a research-type MRI scanner (RAIS 2.0-T) developed at a university laboratory setting. 0 1997 Elsevier Science Inc. Keywords: Acoustic noise; Sound noise; Acoustic noise due to gradient pulsing; Sound noise in magnetic resonance; Analysis of acoustic noise in MRI. INTRODUCTION Since the first magnetic resonance imaging (MRI) con- cept was devised by P.C. Lauterbur, gradient coils and gradient pulsings have been the basic imaging tools for decades. This basic gradient pulsing in conjunction with the magnetic field in MRI produces what is called acous- tic or sound noise. Ever since the appearance of clinical MRI scanners, it has been one of the most disturbing obstacles for MRI patient scanning, especially for psy- chiatric patients and small children.ie3 There have been some attempts to reduce sound noise by using the anti- phase noise-cancellation technique4V5 and the Lorentz- force-cancellation technique.6x7 Most of these techniques have not been very successful and significant sound noise still remains. A simpler and perhaps more widely used technique is the use of ear plugs but this method seems to protect only against sounds transmitted by the auditory canal to the ear and does not protect against sound or acoustic transmission to the brain either directly or indirectly through the body structures, i.e., bones in the skull. In fact, we still experience loud sound noise even after wearing ear plugs since ear plugs suppress only the high-frequency sound noise within the audible frequency band.6 With the increasing role of MRI in the fields of research such as the neural and cognitive sciences, it has become apparent that sound noise is one of the serious noise sources in the measurement of subtle changes in the oxygenation status in the cortex and blood capillar- ies. *-lo Although some studies have been reported,” it is felt that a more quantitative physical analysis of sound noise produced by recently available MRI systems would be an important asset for future research on this impor- tant problem, especially in connection with the newly developing functional MRI and other cognitive science RECEIVED 1l/26/96; ACCEPTED 4128197. Radiological Sciences, University of California, Irvine, Irvine, Address correspondence to Z.H. Cho, Ph.D., Department of CA 92717. E-mail: zcho@uci.edu 815