Computation of electric and magnetic stimulation in human head using the 3-D impedance method

Abstract

A comparative, computational study of the modeling of transcranial magnetic stimulation (TMS) and electroconvulsive therapy (ECT) is presented using a human head model. The magnetic fields from a typical TMS coil of figure-eight type is modeled using the Biot-Savart law. The TMS coil is placed in a position used clinically for treatment of depression. Induced current densities and electric field distributions are calculated in the model using the impedance method. The calculations are made using driving currents and wave forms typical in the clinical setting. The obtained results are compared and contrasted with the corresponding ECT results. In the ECT case, a uniform current density is injected on one side of the head and extracted from the equal area on the opposite side of the head. The area of the injected currents corresponds to the electrode placement used in the clinic. The currents and electric fields, thus, produced within the model are computed using the same three-dimensional impedance method as used for the TMS case. The ECT calculations are made using currents and wave forms typical in the clinic. The electrical tissue properties are obtained from a 4-Cole-Cole model. The numerical results obtained are shown on a two-dimenaional cross section of the model. In this study, we find that the current densities and electric fields in the ECT case are stronger and deeper penetrating than the corresponding TMS quantities but both methods show biologically interesting current levels deep inside the brain.

Electrical Bioimpedance Cerebral Monitoring. A Study of the Current Density Distribution and Impedance Sensitivity Maps on a 3D Realistic Head Model

“…For the calculations of simulated electric current field in the human head model, we used a 3-D impedance method [27][28][29]. The head model is described using a uniform 3-D Cartesian grid and composed of small cubical cells, called voxels, 1x1x1 mm.…”

Magnetic‐field‐induced vertigo: A theoretical and experimental investigation

“…Information about the magnitude of current density in the inner ear needed to induce vertigo-like effects can be inferred from the results of GVS studies, but again it is not straightforward to relate the internal induced current to the currents applied to the mastoids. By extrapolating from calculations related to ElectroConvulsive Therapy (ECT) [Nadeem et al, 2003] we predict that 1 mA applied to the cranium above the temporal lobe might generate a typical current density of the order of 100 mAm À2 in brain tissue near to the inner ear. Transcranial direct current stimulation (tDCS) uses similar current strengths to those used in GVS and current densities of 100 mAm À2 in the brain are assumed [Nitsche et al, 2003[Nitsche et al, , 2004.…”

Electrical Bioimpedance Cerebral Monitoring

“…For the calculations of simulated electric current field in the human head model, we used a 3-D impedance method [27][28][29]. The head model is described using a uniform 3-D Cartesian grid and composed of small cubical cells, called 2 [Online] Available on March 23rd,2007: http://niremf.ifac.cnr.it/tissprop/ voxels, 1x1x1 mm.…”