Influence of anisotropic compartments on magnetic field and electric potential distributions generated by artificial current dipoles inside a torso phantom.

The purpose of this study is the analysis of the influence of anisotropic conductivity on magnetic fields and electric potentials by means of phantom measurements. An artificial rotating current dipole was placed in the middle of an anisotropic skein arrangement in a torso phantom filled with saline solution. The signal strength and the change of the shape of potential and field patterns due to anisotropic volume conduction were investigated. Different directions of the dipole were compared to corresponding orientations of measured fields and potentials (angle difference). For electric and magnetic data, the angle difference between observed signal orientations and true dipole orientations continuously increased with the angle between dipole and anisotropy (up to 80 degrees ) and then decreased back to zero at their orthogonal orientation. Both signal strengths decreased about 10% with an increasing angle between dipole and anisotropy. While the magnetic field showed a generally stronger shape change, the changed shape of the electric potential showed similarity to an extended source. Our phantom study demonstrated that anisotropic compartments influence directions, amplitudes and shapes of potentials and fields at different degrees. We concluded that anisotropic structures should be considered in volume conductor modelling, when source orientation, extension and strength are of interest.