Modeling of cardiac electrical activity for characterizing vortex components

Abstract

In this study, source model for solving biomagnetic inverse problem is developed with a new method, where vortex components along with the flow component of the equivalent source is considered. The model is an aggregation of a single current dipole and a magnetic dipole. The single current dipole denotes the flow component while the magnetic dipole is an abstract of the vortex component of the biomagnetic source.Simulation results indicate that this model could be more efficient for modeling cardiac electrical activity, compared with single current dipole. Despite that this model is more complicated than the single current dipole model; simple algorithm can still be used for solving inverse problem with only small revision. Meaning of the model parameters solved from the inverse problem is also discussed.Keywords-Modeling; Magnetocardiography; vortex source; magnetic dipole; current dipole I.INT RODUCTION Magnetocardiography (MCG) and Electrocardiography (ECG) are both non-invasive biomedical functional imaging method for cardiac electrical activ ity. However, the problem is whether these two approaches could provide complementary information for each other.Some theoretical and experimental efforts have been made to verify that MCG could provide more valuable information besides ECG. In 1982, Wikswo et al. suggested that a kind of electrically silent magnetic field could be detected by magnetic detection device [1]. Brockmeier et al. proved this theory by experiments [2]. They found that when the subjects were stress induced, there were dramatic changes in the MCG while no comparable changes in the mu lti-lead ECG. One of the most recent works in this area was reported by Haueisen et al, who found different patterns of the mapping of MCG and ECG produced by artificial open loop current in a body phantom [3]. In other words, MCG surely provides some differentiating information about the electrical activity besides the ECG.According to the Helmholtz theory, the equivalent source of electrical activ ity, either electrical potential or current, consists of a flow (rectilinear) component and a vortex (close-loop) component [4]. ECG can only provide the information about the flow part of the electrical potential source. But MCG can detect the magnetic field produced by both vortex and flow part of the current source [2]. This brings the difference between mappings of MCG and ECG. So models of the cardiac current source in MCG study should include the vortex co mponent of the source.In this study such a model for the equivalent source of cardiac electrical activity is proposed. In section the mathematical fundament of our model is presented. Higherorder terms in mu ltipole expansion is o mitted to obtain this new equivalent model. It can be formatted as an aggregation of a single current dipole and a magnetic dipole (Equivalent Current and Magnetic Dipole, ECMD). In section , we simulate the characteristics of the field produced by our model and compare this model with an equivalent single current dipole model. In secti...