Fig. 1.

(A) The coil placement to E-field mapping table contains E-fields in the ROI for all coil placements, where N_t is the number of tetrahedra in ROI, N_c is the number of coil positions, and N is the number of coil placements (N = 360N_c). Each column of the table is the induced E-field in every ROI tetrahedron for a fixed coil placement. Each row of the table denotes the E-field induced in a fixed tetrahedron for all possible coil placements. For each coil placement, orientations are defined by rotating the coil tangent to the scalp and about its center as shown. Here a local coordinate axis $\left(x_{j_1},y_{j_1}\right)$ tangential to the scalp and centered about the coil is defined by setting the ${\widehat{y}}_{j_1}$ unit vector pointing posterior to anterior. The angles are defined as the polar angle on this coordinate system. Example coil orientations corresponding to j₂ = 45° , 90° , and 135° are shown for several coil positions. (B) TMS coil positions are denoted by black dots over the scalp of the head model and are typically chosen on a large region covering the ROI (red region).