Improved subject´s safety in simultaneous EEG and fMRI recordings using solid state switching devices on the electrodes

The current trend in simultaneous electroencephalographic (EEG) and functional Magnetic Resonance Imaging (fMRI) measurements is towards increasing the number of EEG channels while performing fMRI recordings at higher magnetic field strengths. As the static magnetic field increases, simultaneous EEG/fMRI recording raises important patient safety issues, mainly due to RF-induced electromotive forces (EMF) in closed loops. These induced currents can potentially cause either burning or peripheral nerve stimulation. In this work we address such potential safety hazards by introducing on the tip of EEG electrodes two JFETs connected in totem pole as nonlinear current limiting devices, which are externally triggered to close during MR scanning periods. The proposed circuit does not interfere with simultaneous EEG and fMRI recordings, due to the extremely low channel resistance of the devices and the availability of JFETs with non-magnetic metallic leads