Electroencephalogram Electrode and Amplifier Temperature Changes During Routine Anatomical and Functional Magnetic Resonance Imaging Sequences at 3 Tesla

Abstract

Magnetic resonance imaging (MRI) sequences commonly used in simultaneous electroencephalogram (EEG)-MRI studies include blood oxygenation level-dependent (BOLD) and anatomical T1-weighted MRI. Safety and electrode heating profiles for these sequences have been well-characterized. However, recent improvements in EEG design may allow for additional sequences to be performed with similar expectations of heating safety, which would expand the EEG-MRI infrastructure for quantitative physiological studies. We evaluated temperature changes ex vivo and in vivo over a wider range of preparation and readout modules with differing specific absorption rate (SAR). A 32-channel EEG cap was used at 3 T and ex vivo heating was assessed for 2D- and 3D-pseudo-continuous-arterial-spin-labeling, 2D-cine, 2D-phase-contrast, 2D T2-Relaxation-Under-Spin-Tagging, 32-direction b = 1000 s/mm2 and b = 2000 s/mm2 2D-diffusion tensor imaging, multiband-BOLD, 3D-T1 MPRAGE, 3D-FLAIR, and 3D-T2. Temperature was monitored with a fiberoptic probe system and plotted over six different electrodes, the amplifier, and battery pack. In vivo assessments were conducted in three participants with the same system. A further in vivo supplemental cohort (n = 10) was used to further evaluate qualitative self-reported heating. Device integrity was evaluated by the manufacturer following experiments. Peak temperature and maximum temperature increases were 23.0°C and 0.4°C respectively ex vivo, and 37.6°C and 0.7°C respectively in vivo. Temperatures did not approach the safety heating threshold of 40°C (defined as a conservative threshold based on manufacturer recommendations and burn injury data). Participants completed in vivo scans without adverse events. No manufacturer-reported device damage was identified. Overall, the tested scans induced heating below critical limits at the clinical field strength of 3 T.