Simultaneous EEG and fMRI: T1-based evaluation of heating in a gel phantom at 3 Tesla

Abstract

EEG electrodes and leads, comparable to metallic implants, can lead to heating of tissue when used in an MRI scanner. Simultaneous EEG and fMRI experiments are frequently carried out at 3 T or higher fields. High field strength, and thus high-energy RF pulses, added to complex EEG lead configuration increases the risk of severe localized heating, or hot spots. Unlike the skin, the brain lacks thermoreceptors, and the subject might not report anything unusual during the scan although hot spots may occur. In simultaneous EEG and fMRI experiments, the temperature at individual electrode sites can be monitored using optic fibre temperature probes. To complement the isolated surface temperature readings, we aimed to map the whole temperature distribution within a phantom. An EEG-equipped gel phantom was imaged using a T1-weighted sequence before and after running a high-energy MR sequence at 3 T. Changes in T1 intensity profile would indicate a relative temperature increase. In our setting, hot spots were not detected in the relative temperature maps of the phantom. Optic fibre temperature probes at selected electrode sites indicated small temperature increases depending on the MR sequence used. The phantom core temperature remained unchanged. RF energy distribution can vary with electrode configurations and MRI scanners. We suggest that EEG equipments should be tested for safety reasons. The MRI thermometry –inspired relative T1 intensity method provides an easy way to test possible heating within a phantom.