This invention discloses methods and apparatuses for 3D imaging in Magnetoencephalography (MEG), Magnetocardiography (MCG), and electrical activity in any biological tissue such as neural/muscle tissue. This invention is based on Field Paradigm founded on the principle that the field intensity distribution in a 3D volume space uniquely determines the 3D density distribution of the field emission source and vice versa. Electrical neural/muscle activity in any biological tissue results in an electrical current pattern that produces a magnetic field. This magnetic field is measured in a 3D volume space that extends in all directions including substantially along the radial direction from the center of the object being imaged. Further, magnetic field intensity is measured at each point along three mutually perpendicular directions. This measured data captures all the available information and facilitates a computationally efficient closed-form solution to the 3D image reconstruction problem without the use of heuristic assumptions. This is unlike prior art where measurements are made only on a surface at a nearly constant radial distance from the center of the target object, and along a single direction. Therefore necessary, useful, and available data is ignored and not measured in prior art. Consequently, prior art does not provide a closed-form solution to the 3D image reconstruction problem and it uses heuristic assumptions. The methods and apparatuses of the present invention reconstruct a 3D image of the neural/muscle electrical current pattern in MEG, MCG, and related areas, by processing image data in either the original spatial domain or the Fourier domain.