A Novel Approach on dTMS Coil Design Based on Tractography and Neural Cable Theory

Deep transcranial magnetic stimulation (dTMS) plays a useful role in the treatment of many diseases. In previous designs, it is only desired to maximize the absolute value of the electric field in the target zone. Whereas due to the nerve cable equation (NCE), the membrane potential of a nerve cell is changed due to the rate of change in the tangential electric field [Formula]. In this paper, the criterion of the design is to maximize [Formula] along the nerve cell fiber and simultaneously minimize the absolute value of the electric field. The direction of the nerve fibers is obtained using Tractography. Then, the specifications of source and coils such as position and spatial angles are determined in such a way that every two coils cancel the absolute value of the electric field of each other by using reciprocity theorem. This happened whereas the [Formula] is maximized. For better comparison, a 20-coil array is designed for stimulation of cingulum region of the brain. Results of this array are compared with results of the FO8-Halo coil and it is shown that with the same value for [Formula], an absolute value of the induced field in the brain for the 20-coil array is much smaller than the FO8-Halo coil. Also, designed coil array requires smaller sources. So, the array can stimulate the target zone more accurately and with higher efficiency. This new technique can solve the problem of stimulation of the large areas of the brain and stimulate the desired target zone with more accuracy.