Ultra-low-field magnetic resonance imaging combined with magnetoencephalography

Human brain activity can be monitored with magnetoencephalography (MEG) by measuring the femtotesla-level extracerebral magnetic fields with SQUID magnetometers. On the other hand, the structure of the brain can be determined with magnetic resonance imaging (MRI), where the applied fields may be 15 orders of magnitude higher than the smallest neuromagnetic signals, ruling out simultaneous MEG. It has been demonstrated recently that simultaneous MRI and MEG is possible: the trick is prepolarization at about 0.1 tesla and MRI at about 0.1 mT. We have designed and are building a hybrid multichannel helmet-shaped MEG-MRI device, which will be capable of simultaneous ultra-low-field MRI and MEG.