Cerebral mapping: A comparison of electroencephalographic images and blood oxygenation weighted MR images
Abstract
Combination of EEG and functional MRI reveals more information about brain activity than either one does separately. The EEG has good temporal resolution but coarse spatial resolution, whereas the functional MRI has good spatial resolution but moderate temporal resolution. Thus, combining the EEG with the MPI gives the spatiotemporal characteristics of cerebral functions. The purpose is to compare the locations of cerebral sources from the EEG using a newly developed ellipsoidal model and a commonly used spherical model and from the functional MRI. The comparison indicates the accuracy of the locations for each model. To obtain source locations, EEG from nine adults with 10/20 standard nineteen electrodes on the scalps were acquired with right-median stimulation before MRI scanning. Then, functional MR images and anatomical MR images from the subjects each in a 3T magnet core were obtained with the same stimulation and without it. Consequently, the EEG provided source localizations and the functional MRI the locations of evoked BOLD regions. Also, the anatomical images having the estimated head dimensions helped construct four-shell ellipsoidal and spherical models to localize the sources. Thus, the averaged potentials from the EEG were interpolated with three variable splines and then transformed to spline-based Laplacians. The Laplacians each were fit to the similar data generated by sources in each type of the models with the Marquardt method. Consequently, comparing the resulting EEG source locations with the BOLD sites spatially resulted in the distances between them. The average distance between the sources and the BOLD regions for four-shell ellipsoidal models was 13.6 millimeters with a range of 5.3 to 30.0 millimeters. Similarly, the average distance for four-shell spherical models was 21.5 millimeters with a range of 7.4 to 40.7 millimeters. The ellipsoidal sources were as close to the central sulci as the BOLD regions were, but the spherical sources were at least twice as far as the ellipsoidal sources. Consequently, the ellipsoidal models provide better accuracy of source localizations than the spherical models. Therefore, an ellipsoidal model for EEG and functional MRI is suitable for tracking cerebral sources in time and space.
This paper has been withdrawn.