Application of superconducting magnetometers to the measurement of the vector magnetocardiogram

A differential magnetometer, a molypermalloy magnetic shield, and a digital data acquisition system have been developed for detailed analysis of the human vector magnetocardiogram (VMCG). With this system, the VMCG can be recorded at any desired point around the subject's thorax while simultaneously recording the vector electrocardiogram (VECG). To simplify analysis of the three-dimensional time dependent vector magnetic field, the spatial variation of the VMCG can be described in terms of the field produced by an effective source such as a magnetic multipole series. We find the VMCG field from normal subjects to be sufficiently dipolar that a magnetic dipole alone can be used to describe the major features of the VMCG. A partial inversion of the dipole field equations and numerical analysis techniques are used to determine the components and location of the dipole that provides the least-squares fit of the dipole fields to the observed ones.