On the contribution of volume currents to the total magnetic field resulting from the heart excitation process: a simulation study

Data from a simulation study of volume current contribution to the total magnetic field produced in the heart excitation process is presented. Contributions from different tissue types are analyzed and effects of torso size are studied. A high resolution finite element model of an adult male torso composed of 19 tissue types is used. It has detailed description of tissue geometries and therefore is well suited for analyzing the contribution of the primary and secondary currents to the magnetic field. The computed results show major contribution of volume currents from blood, myocardium, and lungs and less significant contribution from liver, muscle, and other tissues. The contribution to the volume currents from the blood in the ventricles was highest. These simulations suggest that contribution to the total magnetic field due to volume currents flowing in tissues other than blood could be accounted for by simply multiplying the total field values by a constant. Values of these multipliers would be based on the tissue type and time in the excitation cycle. Effects of torso size on the computed magnetic fields are also evaluated. Our data shows that a torso extending approximately 3 cm above and below the heart produces field patterns similar to a larger torso model extending from top of guts to the bottom of neck. Thus a shorter torso model would be sufficient for cardiac magnetic field analysis. These results are of interest for future modeling of magnetocardiograms and solving the inverse problem.