Evaluating the electrode measurement sensitivity of subdermal electroencephalography electrodes

Abstract

This paper studies the effect of subdermal EEG lead placement on measurement sensitivity distributions, and compares them with the sensitivity distributions obtained using surface EEG leads. A five-layered isotropic head model was constructed based on magnetic resonance imaging (MRI) data. The surface electrodes were placed on the scalp of the model according to the traditional 10-20 EEG system. The subdermal electrodes were arranged in 5 × 5 grids and placed on the skull in seven reference locations: FZ, CZ, OZ, T3, T4, P3, and P4. The effects on the measurement sensitivity were studied by means of the half-sensitivity volume (HSV). For the surface measurements, the size of the HSV varies around 1 cm3, while the subdermal leads can concentrate the measurement in regions ten times smaller. The results indicate that the EEG measurement may benefit from subdermal implantation since the subdermal measurements are more accurate and specific than the surface measurements. Nevertheless, the improvement was registered only for the subdermal grids centred on CZ, T3 and T4 locations. This suggests that the subdermal electrode performance highly depends on the thickness of the underlying matter, such as the skull and cerebrospinal fluid (CSF).