Simultaneous EEG and fMRI is possible even at ultra-high 9.4 Tesla field strength
Modern neuroimaging methods that enable measurement of brain function without opening the skull of the experimental subjects are truly amazing. Currently, there are multiple non-invasive neuroimaging methods available, however, each of them is limited either in terms of spatial or temporal resolution. For instance, functional magnetic resonance imaging, while being spatially accurate down to the millimeter scale, suffers from compromised temporal resolution. Conversely, electroencephalography is temporally highly accurate (~milliseconds), but due to the ill-posed electromagnetic inverse problem the spatial accuracy of the method is rather limited. There are computational methods that make it possible to combine complementary information provided by the different methods, but in an ideal case the measurements should be conducted simultaneously. However, recording electroencephalography during functional magnetic resonance imaging has been highly challenging due to the strong magnetic fields producing artifacts to the recorded signal.
In their recent study, Neuner et al. (2012) extended their previous work to test whether electoencephalography can be reliably recorded at an ultra-high 9.4 Tesla field strength. Their results indicate that the artifacts due to cardiac activity (that induce slight movement of the subject and thus induction of currents to the electrodes) increased in amplitude at 9.4 field strength but that it was still possible to measure meaningful and replicable electroencephalographic signals at this ultra-high field strength. The authors further demonstrate that independent component analysis is a useful method for separating artifacts from relevant electroencephalographic signals at the extremely challenging recording conditions. While these measures were obtained under conditions of static magnetic field and gradient switching that takes place during functional imaging does introduce additional artifacts, this demonstration by the authors is nonetheless promising and there are ways to circumvent the disturbances caused by gradient switching, such as inter-leaved acquisition (see, for example, Bonmassar et al. 2002).
Neuner I, Warbrick T, Arrubla J, Felder J, Celik A, Reske M, Boers F, Shah NJ. EEG Acquisition in Ultra-High Static Magnetic Fields up to 9.4T. Neuroimage (2012), online publication ahead of print. http://dx.doi.org/10.1016/j.neuroimage.2012.11.064
Bonmassar G, Purdon PP, Jaaskelainen IP, Solo V, Brown EN, Belliveau JW. Motion and ballistocardiogram artifact removal for interleaved recording of EEG and ERP during MRI. Neuroimage 16:1127-1141, 2002. http://dx.doi.org/10.1006/nimg.2002.1125