High-T/sub c/ SQUID-based impedance magnetocardiography

We report impedance magnetocardiography (I-MCG) measurements carried out in a partially shielded environment. In these measurements, a small-amplitude ac current is injected through the torso via outer electrodes and the ac magnetic fields are probed with a high-Tc SQUID magnetometer. We have also performed simulations using an axisymmetric finite element method (FEM) model in order to predict the SQUID response to changes in tissue conductivity and blood volume during the cardiac cycle. The heart is modeled as a nested sphere inside an idealized conducting thorax. The current density and resulting magnetic field are calculated during two phases of the cardiac cycle. Calculated field values are compared to experimental results. FEM simulations are extended to model the induced current density and SQUID response during noncontacting I-MCG.