Non-invasive focalized stimulation in deep brain using the spatially symmetric array

As a non-invasive neuromodulation technology, transcranial magnetic stimulation (TMS) shows great potential in the treatment of mental diseases. Using TMS to stimulate deep brain targets has significant scientific research value for the exploration of the causes of psychiatric diseases. However, the focalized induced electrical field (E-field) generated by traditional TMS coils or coil arrays is largely restricted to superficial cortical targets. To achieve focalized stimulation in the deep brain, a novel spatially symmetric array based on curved θ-type coils (the θ-SSA) is proposed in this paper. Four θ-type coils in the array are symmetrical to the YZ and XZ planes. Each θ-type coil is placed tangent to the human scalp and bent away from the human head to reduce the non-longitudinal component accumulation of the induced E-field and enhance the stimulation focalization. The finite-element method is used to obtain the 3D spatial distributions of the intracranial induced E-field generated by the proposed array. Results show that the θ-SSA can form an obvious focusing area in the deep brain 11 cm below the scalp. Under identical stimulation current excitation, the θ-SSA can increase the intracranial longitudinal attenuation ratio by 77% compared to the traditional TMS coil. In addition, when generating the same focusing area, the stimulation depth of the θ-SSA is 1.67 times deeper than that of the traditional TMS coil. Meanwhile, the proposed array can dynamically steer the intracranial stimulated area, and the spatial coordinates of the intracranial stimulation target point can be flexibly and continuously adjusted when changing the stimulation current parameters applied to the array. An anatomically realistic human head model with gray matter is employed in this paper to verify our method.