Abstract: The biomagnetic inverse problem is severely underdetermined. Even with large arrays (100 or more elements) of detectors we cannot measure the entire external biomagnetic field; instead we measure the magnetic field at a finite number of points on some surface. In order to determine the Nyquist sampling interval we must consider a large number of factors including the size of the source, the distance from the source to the pick-up coil, the size of the pick-up coil, the order of the gradiometer, and the baseline of the gradiometer. In this paper, we discuss the effects of the pick-up coil size and of the axial gradiometer on the Nyquist sampling interval. Our goal is to determine sampling rates for specific sources measured with circular pickup coils of various diameters. As an example of the effects of undersampling the magnetic field, we present reconstructed current densities from over- and undersampled data. !7
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