Table 1.
Electrical Properties of Different Tissues with Increasing Model Complexity
| Tissue/Category | isotropic | anisotropic1,2 | dielectric dispersion3,4 | |
|---|---|---|---|---|
| σ (S/m) | σ (S/m) | σ (S/m) | εr | |
| CSF | 1.5 | TF | N/A | N/A |
| Grey matter | 0.23 | TF | TF(ω)3 | f(ω)3 |
| White matter | 0.14 | TF | TF(ω)3 | f(ω)3 |
| Glial scar | 0.13 | N/A | N/A | N/A |
| Dura and arachnoid5 | 3.0×10−2 | N/A | N/A | N/A |
| Skull6 | 2.0 ×10−2 | N/A | f(ω)3 | f(ω)3 |
| Soft tissues7 | 0.33 | N/A | f(ω)3 | f(ω)3 |
Only regions within the brain (including CSF) were treated as anisotropic.
section 2.3 and table 2 summarize how tensors in the brain regions were constructed.
The model was solved using a Fourier approach. The dependence of Σ/σ and εr on angular frequency, f(ω), for brain parenchyma, skull, and soft tissues are from (Gabriel et al., 1996b).
The electrode-tissue interface was modeled as a thin layer (equation 2) with a Faradaic resistance and double-layer capacitance of 150 Ωcm2 and 30 µF/cm2, respectively (Wei and Grill, 2009).
The dura and arachnoid mater were lumped in a thin layer (equation 2) with a thickness of 2.3 mm.
Only the part of the skull that surrounded the brain (figure 1a) was considered.
The muscles, tendons, cervical vertebrae, fat, skin, intervertebral disks, blood, air, and portions of the skull within the soft tissues were lumped into a single conductive region.
Abbreviations: TF = tensor field, CSF = cerebral spinal fluid, σ = conductivity, εr = relative permittivity