+ Human Brain Mapping 447-57(1996) 4 Comparison of Primary Motor Cortex Localization Using Functional Magnetic Resonance Imaging and Magnetoencephalography John A. Sanders, Jeffrey D. Lewine, and William W. Orrison, Jr. Department of Radiology, New Mexico Regional Federal Medical Center, University of New Mexico School of Medicine, Albuquerque, New Mexico 87131 -53.36. + + Abstract: The primary goal of the study was to compare estimates of motor cortex localization from functional magnetic resonance imaging (FMRI) and magnetoencephalography (MEG). Thirteen normal volunteers were studied using both methods. FMRI was performed on a clinical 1.5 T system using gradient-echo acquisitions and basic f-test processing. MEG primary motor field was characterized by a single dipole model. Comparisons between the location of the btst-fitting MEG dipole and the FMRI activation results were made using both fixed regions-of-interest weighted averaging and clustering analysis to reduce the observed FMRI activations to a single representative location. Both FMRI and MEG identified expected anatomic regions of primary motor activity and there was overall agreement to within lfl mm between these two functional imaging modalities. Given the observed agreement between these two techniques, it does not appear that the proposed artifactual mechanisms of local bulk motions or large-vessel sensitivity will seriously preclude the clinical utility of FMRI for preoperative localization of sensorimotor cortex. Key words: magnetic resonance imagng, magnetoencephalography, functional imaging, motor, brain o 1996 WiIey-Liss, Inc. + + INTRODUCTION Accurate localization of cerebral cortical activity is important for surpcal planning in the treatment of such conditions as intractable epilepsy, vascular mal- formations, and neoplasms [Benzel et al., 1993; Orri- son et al., 1990; Sutherling et al., 19881. Whereas identification of sensorimotor cortex in neurologically normal subjects is usually readily accomplished by examination of structural MR data, mass lesions in neurosurgical patients often render strictly anatomical Received for publication March 2,1995; revision accepted October 3, 1995. Address reprint requests to John A. Sanders, Ph.D., University of New Mexico School of Medicine, Department of Radioloby, 915 Camino de Salud NE, Albuquerque, NM 87131-5336. strategies subject to error [Penfield and Boldrey, 1937; Ojemann, 19791. Until recently, the most reliable method of localizing cortical function was by direct intraoperative stimulation or recordings, since visual anatomical localization is known to be inaccurate [Benzel et al., 1993; Orrison et al., 1992; Sutherling et al., 1988; Ojemann, 1979;Wood et al., 1988; Woolsey et al., 19791. Recent developments in both functional magnetic resonance imaging (FMRI)and magnetoencephalogra- phy (MEG) have heightened interest in non-invasive mapping of brain activity. Given the possibility of functional mapping using currently installed instru- mentation, FMRI localization has the potential to be a readily accessible clinical tool. However, the tech- niques that are most often used at 1.5 T are often susceptible to several different artifact sources that o 1996 Wiley-Liss, Inc.