Integration of Functional MRI, Structural MRI, EEG, and MEG

The combination of functional Magnetic Resonance Imaging (fMRI) with Electroencephalography (EEG) and Magnetoencephalography (MEG) source reconstruction techniques promises to add temporal resolution in the [ms] range to fMRI activation maps. Depending on the available information, different co-registration methods for merging structural Magnetic Resonance Imaging (sMRI) and fMRI coordinate systems may be useful. The usage of scanner coordinates as well as landmark-, surface-, and volume-based registration is discussed. Dipole fits can benefit from fMRI constraints: Meaningful seed points for source locations are obtained. A reconstructed dipole in the vicinity of each fMRI hotspot yields the corresponding source time course. Spatially unconstrained dipoles are then necessary to account for remaining activity. Current density reconstructions react upon fMRI constraints in two ways: Activity in the vicinity of fMRI hotspots is bundled. Remaining activity can be localized correctly, if its field distribution cannot be generated from sources within the hotspots, and if the fMRI constraint is imposed softly.