This isotropic model was then compared to a similar model having anisotropic tissue
properties. In the anisotropic model, the spatially-varying electrical conductivity values from the
tensor transformation were used.
Three-dimensional Model
A rectangular volume corresponding to a truncated image array was created using 24,840
quadratic brick elements, with 212,877 degrees of freedom for the dependent variable, V, and
electrical properties calculated for each voxel. Each brick element corresponds to an image
voxel. To reduce computation time, the atria were disregarded and only the ventricles were
modeled when brick elements were used. When the total mass of the heart was required, the
modeling was done with ventricle and atria volumes.
Figure 3-4. Mesh containing 24,840 brick elements corresponding to embedded ventricles and
surrounding media.
The continuity equation for conductive DC media yields a general form of Ohm's law,
which for a static case states that
V- J =-V-(G'VV- JF)= 0 (3-4)
where Je is an externally generated current density, Jis the induced current density, Vis the
electric potential, and G'is the electrical conductivity. A current source term, Q, was included,
and the externally generated current density was eliminated. Therefore, the following generalized
equation was used