A torso phantom for the assessment of active and passive vortex currents

We developed a realistically shaped physical torso phantom for the assessment of the influence of active and passive vortex currents on the magnetocardiogram (MCG) and the electrocardiogram (ECG). Active vortex currents were produced by twelve circularly arranged single dipoles. Passive vortex currents were created with the help of a single dipole inside a hollow cylinder. The conductivity of this hollow cylinder compartment was varied systematically, while the torso compartment conductivity was kept constant. We measured simultaneously magnetic and electric signals. Source localization was performed with the help of boundary element models. For the passive vortex currents we found that an increased conductivity ratio (hollow cylinder to torso) caused a slight increase of the magnetic signal strength and a strong decrease of the electric signal strength. For the active vortex currents we found that the more vortex shaped these currents were the more the electric signal strength decreased. In this case, the magnetic signal strength was not influenced. Source localization for the active vortex current model was found to be more accurate when using magnetometer signals as compared to gradiometer signals or electrode signals. For the passive vortex current model we found dipole localization errors of up to 16mm when using a homogeneous torso model. In conclusion, vortex currents might explain the experimentally observed differences between MCG and ECG recordings.