In biomagnetic inverse problems different models of the source activation can be used depending on the physiology of the problem. In this study we compared different source models to perform current source reconstruction in MCG. We first considered a single dipole source model using a non linear minimization algorithm to localize the source of the heart activity in different segments of the MCG signals. We then repeated the same analyses using a distributed sources model and calculated an equivalent dipole located in the center of mass of all dipoles to compare it with the results of the single dipole model localization. The differences in the positions and orientations were evaluated under different conditions, for normal subjects at rest and after stress exercise test, using normal component and vector component data. Different configurations of the volume conductor model were used, to evaluate the influence of the geometry and of the conductivity inhomogeneities on the inverse solution. The results show that 3D data allow finding smaller differences between the single dipole and the equivalent dipole localized solutions.
In this paper we present the analysis of 3D measurements of the magnetocardiogram by means of current source reconstruction. The data considered are rest and exercise stress data of test subjects. The source model used to describe the heart activation is a distributed source model, which allows to follow how the heart activation spreads over the myocardium. We developed a four compartments human torso model including the heart cavity and two lungs. Different values of the compartment conductivities are used to study the effect of the inhomogeneities on the reconstructed sources. The comparison between rest and stress data is done by means of correlations coefficients that indicate how close the reconstructed sources are in terms of dipoles moments, since in the source model considered the dipoles positions are fixed and depend on the source space model geometry. The same analyses are repeated using the 3D magnetic data and only the normal component, to investigate the additional information given by the tangential components. The results show that the torso and heart conductivities have a stronger influence than the one of the lungs, and that the 3D data are less sensitive to the changes of the compartment conductivities.
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