Abstract
Physical head phantoms allow the assessment of source reconstruction procedures in electroencephalography and electrical stimulation profiles during transcranial electric stimulation. Volume conduction in the head is strongly influenced by the skull, which represents the main conductivity barrier. Realistic modeling of its characteristics is thus important for phantom development. In the present study, we proposed plastic clay as a material for modeling the skull in phantoms. We analyzed five clay types varying in granularity and fractions of fire clay, each with firing temperatures from 550°C to 950°C. We investigated the conductivity of standardized clay samples when immersed in a 0.9% sodium chloride solution with time-resolved four-point impedance measurements. To test the reusability of the clay model, these measurements were repeated after cleaning the samples by rinsing in deionized water for 5 h. We found time-dependent impedance changes for approximately 5 min after immersion in the solution. Thereafter, the conductivities stabilized between 0.0716 S/m and 0.0224 S/m depending on clay type and firing temperatures. The reproducibility of the measurement results proved the effectiveness of the rinsing procedure. Clay provides formability, is permeable to ions, can be adjusted in conductivity value and is thus suitable for the skull modeling in phantoms.
Acknowledgments
We would like to thank the Technical Expert, Chamber of Crafts, Erfurt, Germany, Mr. Stefan Hasenöhrl, who supported us in the selection of clay types and manufactured the clay samples. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 686865 (project BREAKBEN), from the Thuringian Ministry of Economic Affairs, Science and Digital Society under FGR 0085 (project BASIs), and from the German Research Foundation under grand number HA 2899/21-1.
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