Scalp voltage response to conductivity changes in the brain in the application of electrical impedance tomography (EIT)

Abstract

EIT is a technique to image conductivity distribution which can be used to localize the response region in the brain to stimulation. The response could be originated from neurological activities or the change of cerebral blood volume. The scalp voltage could be used to localize as well, but the voltage response may be too small depending on many factors i.e. the frequency of excitation current, the volume of activated regions, which is hardly detected by an EIT machine. In this study, we investigated based on simulation on two realistic head models generated by MR images. An inclusion was generated in the brain region as a representative of blood. The result shows that the increase of conductivity due to the inclusion caused the decrease of voltage the scalp. The larger volume of the inclusion also led to the decrease of the voltage. When the frequency of the excitation current increased, the voltage response became lesser in amplitude, in particular at the 50 kHz. The minimum of voltage response was -3.19 µV or -0.016% at 50 Hz, and the maximum of the voltage response was -83.87µV or -0.35% at 50 kHz. This indicates that even though the scalp voltage can be used to localize the source of response, it is still challenging for designing an EIT machine to be able to detect the very small response voltage. © 2018 IEEE