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In this paper, an attempt is made to simulate and compare spatio-temporal VCG and VMCG derived from epicardial potentials. Electric (EHV) and Magnetic heart vectors (MHV) are computed from the ECG and MCG at various time instants and their orientations with respect to time are found to show a reasonable tilt of 90 to 100 degrees. The complimentary information with reference to the orientation of cardiac vector offered by MHV could be attributed to its sensitivity to intracellular myocardial currents, while EHV exhibits the orientation associated with only the extracellular currents owing to volume conduction. By comparing the orientations of EHV and MHV generated from a simulated equivalent current dipole model, the present work demonstrates the usefulness of these spatiotemporal vectors in tracing the cardiac current flow inside the thorax for a healthy heart. It could be thus expected that clinically relevant information could be obtained if the present analysis is extended to highly complex and irregular cardiac activation sequences that could be seen in arrhythmia and myocardial infarction. The main contribution of this paper is to mathematically model and derive the magnetic heart vectors from the MCG system extracted from IGCAR lab and verify it with the conventional VCG extraction.. [ABSTRACT FROM AUTHOR]

• Measurement of MCG with First order gradiometer in unshielded environment. • Noise cancellation capability of gradiometer augmented by EEMD technique. • Detailed comparison of MCG measured in shielded and unshielded sites. • Method used is suitable for unshielded MCG for deeper cardiac source estimations. Measurement of weak magnetic fields generated by the electrical activity of the heart is known as magnetocardiogram (MCG). MCG is usually measured using highly sensitive Superconducting Quantum Interference Devices (SQUIDs) inside a Magnetically Shielded Room (MSR). Since MCG signals have a relatively higher amplitude, researchers have attempted to measure MCG in poorly shielded or even in unshielded environments using higher order gradiometers to cancel excess noise. However, they also attenuate signals of interest, especially, those originating from deeper sources. Here, we report a feasibility study to examine the suitability of use of First Order Gradiometers (FOG) to measure MCG in a totally unshielded environment. Usually, conventional noise reduction methods involve averaging of a large number of cardiac cycles aligned by R-peak time instants derived from a simultaneously recorded electrocardiogram (ECG). In addition to this, here we employ a novel noise reduction approach based on Ensemble Empirical Mode Decomposition (EEMD) technique to manage the fall in Signal to Noise Ratio (SNR) in unshielded environment. The study demonstrated an improvement in SNR of about 18 dB in unshielded setup measured using a four channel low T C -DC SQUID system when tested on eight healthy subjects and one subject with a known cardiac dysfunction. MCG traces were measured across different locations on the thorax and the spatial distribution of cardiac magnetic field is visualized using magnetic field maps. The resulting data have been critically evaluated and compared with those derived from MCG measurements made inside the MSR and encourages its clinical utility. [ABSTRACT FROM AUTHOR]