What is the clinical evidence from this study?

Study design: Other. Intervention: Gelatine based head phantoms vs. Electrical equivalent models and ex vivo porcine skin. Primary outcome: Contact impedance response (magnitude and phase) and group delay.

January 1, 2021Open Access

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

Key Result

Gelatine-based head phantoms can accurately mimic the frequency response properties of the human body-electrode system, with electrical properties tunable via gelatine and NaCl concentrations.

Structured PICO

Population

Ten different gelatine-based head phantom configurations and ex vivo porcine skin models

Intervention

Varying concentrations of gelatine (16.9% to 31.6% per mass) and sodium chloride (NaCl, 0-10%)

Comparator

Previously reported electrical models of Ag/AgCl electrodes placed on human skin and a model made from ex vivo porcine skin

Outcome

Electrical properties including contact impedance magnitude, phase response, and group delay over 7 days for a.c. frequencies in the range 20-1000 Hzsurrogate

Gelatine phantoms can be electrically tuned using different concentrations of gelatine and NaCl to accurately mimic the frequency response properties of the human body-electrode system for testing electrophysiological instrumentation.

Limitations

Did not measure the change in mass over time to calculate effective changes in gelatine and NaCl concentrations.
No hair present on the phantoms or porcine skin, which is a major obstacle in practical EEG applications.
Did not evaluate all possible configurations of phantom setups (e.g., internal electrode material, size, external electrode choice).
Did not attempt to mimic the mechanical properties of the body together with the electrical properties.
Frequency range of test equipment was limited to a lower cut-off of 20 Hz.
Cannot separate the cause of the changes presented in the results (whether due to changes in gelatine, internal electrode, or gelatine-electrode interface).

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 frequency and duration of use. This paper investigates ten different phantom configurations, characterising the impedance of the gelatine and electrodes, comparing this to both previously reported electrical models of Ag/AgCl electrodes placed on human 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.

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