Feasibility of an intracranial EEG–fMRI protocol at 3 T: Risk assessment and image quality

Abstract Integrating intracranial EEG (iEEG) with functional MRI (iEEG-fMRI) may help elucidate mechanisms underlying the generation of seizures. However, the introduction of iEEG electrodes in the MR environment has inherent risk and data quality implications that require consideration prior to clinical use. Previous studies of subdural and depth electrodes have confirmed low risk under specific circumstances at 1.5 T and 3 T. However, no studies have assessed risk and image quality related to the feasibility of a full iEEG–fMRI protocol. To this end, commercially available platinum subdural grid/strip electrodes (4 × 5 grid or 1 × 8 strip) and 4 or 6-contact depth electrodes were secured to the surface of a custom-made phantom mimicking the conductivity of the human brain. Electrode displacement, temperature increase of electrodes and surrounding phantom material, and voltage fluctuations in electrode contacts were measured in a GE Discovery MR750 3 T MR scanner during a variety of imaging sequences, typical of an iEEG–fMRI protocol. An electrode grid was also used to quantify the spatial extent of susceptibility artifact. The spatial extent of susceptibility artifact in the presence of an electrode was also assessed for typical imaging parameters that maximize BOLD sensitivity at 3 T (TR = 1500 ms; TE = 30 ms; slice thickness = 4 mm; matrix = 64 × 64; field-of-view = 24 cm). Under standard conditions, all electrodes exhibited no measurable displacement and no clinically significant temperature increase (  2.0 °C) that in some cases exceeded 10 °C. Induced voltages in the frequency range that could elicit neuronal stimulation (