Conventional transcranial electric stimulation (TES) mostly facilitates two rubber electrodes manually attached to the scalp with rubber bands. This procedure is burdensome for participants and staff, lacking reproducibility and limiting montages to a few electrodes. The use of large rectangle electrodes results in rather diffuse and unspecific distributions of the injected electric field.

We provide a simulation framework for various specific applications of TES e.g. retina stimulation or innovative high definition electrode geometries.

For transorbital stimulation of the retina, we indicate the possibility to target specific areas in the retina conceivably of interest when addressing individual conditions of ophthalmic diseases.

When targeting specific areas in the brain, we provide several approaches:
One innovative electrode application is the use of a concentric montage, where simulation results of the electric field spread originating show radially stimulation of a rather focalized area.

Another application approach has two aims: we introduce a flexible cap with 19 fixed electrode positions and provide a framework for determining the distribution of stimulation currents across those electrodes. A flat knitted cap of flexible fabric with 19 integrated stimulation electrodes of silver-coated polyamide threads with electrolyte reservoirs that are encapsulated by diffusion barriers of silicone. To compute the distribution of the stimulation currents for the novel cap, we used the framework of Helmholtz reciprocity.

Comparing positions of the conventional rubber band and the new cap electrodes, drifts of 7.4 ± 3.8 mm in rubber band and 2.0 ± 0.9 mm in the cap electrodes were found over a time course of 30 min. Stimulation configurations including different number of electrodes generated mean electric field strength of 0.1 V/m at targets with mean cosines of angles between target and electric field orientation of 0.55 (focal) and 0.7 (spread).

We introduce a physical head phantom featuring different structural electric conductivities for the validation of simulations and testing of new equipment. Sampling the scalar electric potential in a volume conductor, we can infer on the electric field distribution and compare to simulations. The experimental setting provides the chance to test new hardware on a realistically shaped volume conductor.

With our contributions to theses aspects of TES, we provide innovative application scenarios with supporting information of technical aspects potentially of help in scientific and clinical research.

Presenter: Alexander Hunold

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