An EEG (electroencephalogram) recording system with carbon wire electrodes for simultaneous EEG-fMRI (functional magnetic resonance imaging) recording

Abstract

Simultaneous EEG-fMRI (Electroencephalography-functional Magnetic Resonance Imaging) recording provides a means for acquiring high temporal resolution electrophysiological data and high spatial resolution metabolic data of the brain in the same experimental runs. Carbon wire electrodes (not metallic EEG electrodes with carbon wire leads) are suitable for simultaneous EEG-fMRI recording, because they cause less RF (radio-frequency) heating and susceptibility artifacts than metallic electrodes. These characteristics are especially desirable for recording the EEG in high field MRI scanners. Carbon wire electrodes are also comfortable to wear during long recording sessions. However, carbon electrodes have high electrode-electrolyte potentials compared to widely used Ag/ AgCl (silver/silver-chloride) electrodes, which may cause slow voltage drifts. This paper introduces a prototype EEG recording system with carbon wire electrodes and a circuit that suppresses the slow voltage drift. The system was tested for the voltage drift, RF heating, susceptibility artifact, and impedance, and was also evaluated in a simultaneous ERP (event-related potential)-fMRI experiment.

Altered attention networks in benign childhood epilepsy with centrotemporal spikes (BECTS): A resting-state fMRI study

“…Magnetic resonance artifact was subtracted using adaptive noise cancelation software. After the artifact removal, EEG data were low-pass filtered with a cutoff frequency of 25 Hz and were visually inspected [24]. A trained epilepsy neurologist reviewed the filtered data to identify the epileptic spikes that occurred during scans.…”

Resting functional connectivity between the hemispheres in childhood absence epilepsy

“…EEG data were continuously acquired during fMRI from an EEG cap with 32 carbon wire EEG electrodes (in-house) (Neuroscan Inc., Charlotte, NC) and a preamplifier (in-house). 25 EEG data were recorded with a 125-Hz analog lowpass Butterworth filter (in-house) and digitized at 1 kHz with 24-bit data resolution (SynAmps2, Neuroscan Inc.), referenced online to a linked ear reference electrode. fMRI data were acquired on a 3-T Magnetom Trio scanner (Siemens Medical Systems, Erlangen, Germany) using a standard whole-head coil.…”

“…Magnetic resonance artifact was subtracted using adaptive noise cancellation software. 25 After artifact removal, EEG data were low-pass filtered with a cutoff frequency of 25 Hz and visually inspected. A trained epilepsy neurologist (H.B.)…”

Safety in simultaneous EEG-fMRI at 3 T: temperature measurements

“…Measuring RF-induced heating of an EEG system in MR environment is dependent, for example, on the positioning of the subject and lead configuration (9). In temperature measurements, a wide range of results has been obtained for different field strengths and electrode 1 HUS Medical Imaging Center, Helsinki University Central Hospital, Finland 2 Department of Physics, University of Helsinki, Helsinki, Finland types (2,4,6,8,10). In general, fMRI sequences were considered safe in 1.5 and 3 T (11), whereas in high specific absorption rate (SAR) sequences, such as turbo spin echo (TSE) sequences, significant temperature increases have been observed (8,12).…”