Reducing the Risk of Gradient Induced EEG Hardware Heating During Simultaneous EEG-fMRI
Simultaneous electroencephalography (EEG) and functional MRI (fMRI) has the potential to provide a more complete characterisation of brain function. Acquiring these data simultaneously requires the EEG hardware to be MR safe, since the EEG cap, amplifiers and powerpacks must be located within the MR environment. Placing them in this environment exposes them to both static and varying…
Simultaneous EEG and functional MRI (fMRI) holds the promise of offering a more comprehensive understanding of brain function. Nonetheless, performing these data acquisitions simultaneously within a magnetic resonance (MR) environment exposes the EEG hardware to both static and dynamic magnetic fields. This exposure raises concerns about potential heating risks for the equipment.
Prior research usually situates the amplifiers and power packs outside the MR bore, limiting the heating risk to the EEG cap. However, contemporary guidelines suggest placing the amplifiers within the bore. While this configuration enhances EEG signal quality by minimizing the distance between the EEG electrodes and amplifiers, it concurrently introduces a heightened heating risk for the amplifiers and power packs due to the varying magnetic field gradients.
To investigate the extent of this heating risk, our study was conducted at both 7 Tesla (7T) and 3 Tesla (3T) fields. At 7T, we identified significant heating of the EEG amplifiers when the echo planar imaging (EPI) sequences maintained a slew rate exceeding 88 T/m/s. Implementing a slower slew rate of 61 T/m/s effectively mitigated this heating effect.
At 3T, we replicated the amplifier heating phenomenon and discovered that adjusting the distance between the EEG amplifier/power pack and the magnet's center (isocentre) also impacted the heating risk. By increasing this distance by 30 centimeters, we successfully mitigated the risk of hardware heating, irrespective of the sequence parameters employed, such as slew rate.
Therefore, although optimizing the distance between the electrodes and amplifiers can enhance EEG signal quality and reduce the likelihood of RF heating at the electrodes, the potential for heating in the amplifiers and power packs due to gradient switching becomes a more significant concern. This consideration is particularly pertinent when dealing with the more rapid gradient slew rates present in contemporary MRI scanners, aimed at enhancing spatial resolution.
Consequently, experimenters must carefully evaluate the hardware placement to guarantee the safety of their EEG-fMRI setup, taking into account the varied risks associated with different approaches.
Written by urgent.news from bioRxiv's reporting — not their text. Machine-written — may contain errors; check the original before relying on it.
