OPTIMIZATION OF TEMPORAL INTERFERENCE STIMULATION OF DEEP BRAIN TARGETS BASED ON A PRE-COMPUTED TRANSFER MATRIX

Temporal Interference (TI) stimulation is a modality of Transcranial Electrical Stimulation that uses the interference of two high frequency fields with slightly different frequencies. While being non-invasive, TI has the potential of reaching deep brain targets without exciting the overlying neural tissue. The potential use of TI for the treatment of various neurological disorders requires accurate targeting and increased focality by careful choice of stimulation parameters. We present a novel method for optimizing the location and focality of TI stimulation by computing the optimal electrode positions on the scalp and the applied currents. The starting point of the method is the creation of a digital twin of a subject’s head by segmenting their structural MRI according to tissue conductivity. Possible electrode positions are generated by sampling the scalp with high resolution. A Finite Element solver (SimNIBS) is used to calculate the electric field for each pair of electrodes, resulting in a Transfer Matrix that fully characterizes the forward stimulation problem. Finally, three different algorithms have been designed to choose the stimulation parameters that yield the optimal TI field pattern for any chosen target region in the brain by use of the Transfer Matrix, which needs to be computed only once per subject. Choosing various sub-cortical structures like the hippocampus as targets, our simulations show that this method can produce sub-centimeter stimulation focality. In conclusion, via representative sampling of all possible electrical stimulation fields and intelligent parameter optimization it is possible to achieve deep and focal electrical stimulation.