A vector fetal magnetocardiogram system with high sensitivity

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Abstract
The vector fetal magnetocardiogram (V-FMCG) system that measures the three orthogonal components of the magnetic field from a fetal heart has been developed to clearly observe fetal cardiac activity during pregnancy by using the superconducting quantum interference device. To detect a clear V-FMCG signal, the bottom of the cryostat was made of thin glass–fiber-reinforced plastic and the total length between the pickup coil to the outer surface is 12 mm. Because the cryostat bottom was made thinner, the area of the cryostat’s top and bottom could be made smaller, thus a low evaporation loss (10 days) were obtained. The gantry was able to tilt the cryostat and the bed could move in three axis directions, which made it possible to easily locate the vector pickup coil at an optimum position to obtain the maximum magnetic field from a fetal heart. We obtained V-FMCGs from 21 normal fetuses with gestation periods of 27–38 weeks. Using these vector signals, the dipoles were estimated and the relationship between the strength of the dipole moments and the number of gestation weeks could be obtained. Thus, V-FMCG seems to represent a new noninvasive tool for clearly detecting the electrophysiological activity of a fetal heart.