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 tot al magnetic field produced in the heart excitation process is presente d. Contributions from different tissue types are analyzed and effects of torso size are studied. A high resolution finite dement 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 ana lyzing the contribution of the primary and secondary currents to the m agnetic field. The computed results show major contribution of volume currents from blood, myocardium, and lungs and less significant contri bution from liver, muscle, and other tissues. The contribution to the volume currents from the blood in the ventricles was highest. These si mulations suggest that contribution to the total magnetic field due to volume currents flowing in tissues other than blood could be accounte d for by simply multiplying the total field values by a constant. Valu es of these multipliers would be based on the tissue type and time in the excitation cycle. Effects of torso size on the computed magnetic f ields are also evaluated. Our data shows that a torso extending approx imately 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 n eck. Thus a shorter torso model would be sufficient for cardiac magnet ic field analysis. These results are of interest for future modeling o f magnetocardiograms and solving the inverse problem.