Hybrid coil design for shapeable magnetic field for Transcranial Magnetic Stimulation

Transcranial Magnetic Stimulation (TMS) coils are often designed specifically for either depth brain or focal stimulation [1]. A new technique that provides both depth and focality as well as steerability during TMS using temporal interference (TI). TI TMS operates based on the frequency difference of two stimulation signals that operate in the kHz range. The frequency difference between the two induced electric fields within the brain results in an envelope which provides increased focality of the stimulated area. The brain acts as a complex signal filter which filters out a portion of the higher frequency stimulation and allows the lower frequency difference to dominate [2][3]. Dual site TMS stimulates two areas of the brain with high focality [4][5][6]. Dual site TMS is currently done with two independent coils. Our research on developing novel hybrid coil designs that allow the use of a single TI TMS coil to rapidly steer between different target regions with reduced placement errors and reduced spatial limitations of the chosen targets. Using simulation software, we compare our hybrid designs with single, dual, and butterfly [7] type TMS coils with respect to depth of penetration and focality for dual site TMS.