Part II: magnetic field produced by a current dipole.

To understand the MCG, electrical models of the heart must be used in which the basic building-block is usually the current dipole. The dipole's magnetic field is generally made up of two parts: 1. the contribution by the dipole element itself, which is mathematically simple; 2. the contribution by the current generated in the volume conductor by the dipole, which is complicated and depends on the boundaries; for special boundaries this contribution is zero to Bz, the component of magnetic field which is normal to the boundary. This applies to the boundaries of the semi-infinite volume conductor, the infinite slab, and the sphere. This property allows great simplification in solving the magnetic forward and inverse problems. Because of its importance, it is proven with electrolytic tank experiments. Based on this property, a method is presented for estimating the presence of those dipole combinations which produce a suppressed surface potential; it consists of a visual examination of an "arrow" display of Bz.