Fig. 4. Adaptive (1 kHz based) ECT models for four ECT subjects.

Dynamic FEM models simulated current flow across four subjects who have received ECT (Subject IDs: 21778, 21908.22035, 22615). (First Column) Model anatomy was based on subject anatomical MRI. Static impedance and dynamic impedance values were recorded for each subject (gray box). Each subject model was assigned a specific deep scalp conductivity (${\sigma }_{\text{DS}}$) and a maximum superficial scalp conductivity (${\sigma }_{\overline{\text{SS}}}$) as indicated, such that adaptive FEM simulation predicted corresponding static impedance (based on 2 μA applied current) and dynamic impedance (based on 900 mA applied current) as indicated. (Second and Third Column) Results from the static impedance (2 μA current) simulation showed resulting superficial scalp conductivity and scalp electric field. (Third, Fourth, Fifth Column) Results from the dynamic impedance (900 mA current) simulation showed resulting superficial scalp conductivity, scalp electric field, and brain electric field. We emphasize in these novel adaptive simulations that brain current flow was determined by tissue conductivity and superficial scalp conductivity was simultaneously determined by local electric field. Even for the 2 μA (static) model local changes in scalp conductivity are predicted. For the 900 mA (dynamic) model, the saturation of the transfer function between superficial scalp electric field and conductivity resulted in a more diffuse saturation of scalp conductivity (front of head) compared to scalp electric field (around electrodes).