Electrical properties, accuracy, and multi-day performance of gelatine phantoms for electrophysiology

Abstract

Gelatine based phantoms for electrophysiology are becoming widely used as they allow the controlled validation of new electrode and new instrumentation designs. The phantoms mimic the electrical properties of the human body and allow a pre-recorded electrophysiology signal to be played-out, giving a known signal for the novel electrode or instrumentation to collect. Such controlled testing is not possible with on-person experiments where the signal to be recorded is intrinsically unknown. However, despite the rising interest in gelatine based phantoms there is relatively little public information about their electrical properties and accuracy, how these vary with phantom formulation, and across both time and frequency. This paper investigates ten different phantom configurations, characterising the impedance path through the phantom and comparing this impedance path to both previously reported electrical models of Ag/AgCl electrodes placed on skin and to a model made from ex vivo porcine skin. This article shows how the electrical properties of the phantoms can be tuned using different concentrations of gelatine and of sodium chloride (NaCl) added to the mixture, and how these properties vary over the course of seven days for a.c. frequencies in the range 20-1000 Hz. The results demonstrate that gelatine phantoms can accurately mimic the frequency response properties of the body-electrode system to allow for the controlled testing of new electrode and instrumentation designs.

Investigating Gelatine Based Head Phantoms for Electroencephalography Compared to Electrical and Ex Vivo Porcine Skin Models

“…Owda and Casson: Gelatine phantoms for electrophysiology available at [39] which contains the same results.…”

Signal-Space Projection Suppresses the tACS Artifact in EEG Recordings

“…When constructing the phantom, we only measured the impedance magnitude of the conductive medium. In the next generation phantoms, it is recommended to measure also the impedance phase to makes sure, the phantom perfectly fulfills the quasi-static conditions (Owda and Casson, 2020). However, given the recent measurements in a NaCl based gelatin phantom (Owda and Casson, 2020), it is unlikely that the simple NaCl solution used here would show strong impedance phase within the typical operating frequency range of tACS.…”

Investigating Nuisance Effects Induced in EEG During tACS Application

“…The main rationale behind realizing a hardware demonstrator was that it allowed to acquire data with the full instrumental chain-stimulator, electrode leads, and EEG recorder-in the actual laboratory environment, i.e., including the real power-line interferences (50 Hz and harmonics), amplifier noise and non-linearities, as well as stimulator noise and harmonics. We refrained from using a 3d multi-layer head phantom, like the ones discussed by Owda and Casson (2020) and Vosskuhl et al (2020), as our aim was to obtain sample EEG data for our testing purposes only. Furthermore, we were also not concerned with volume vs. scalp conduction or capacitive electrode impedance effects.…”