Acquisition of Fetal Magnetocardiograms in an Unshielded Hospital Setting

The acquisition of fetal magnetocardiographic signals in various noisy environments is studied, and improvement in the signal-to-noise ratio (SNR) of weak biomagnetic signals is investigated for various noise levels and gradiometer implementations. There is a consistent improvement in the SNR as fetal gestation age (GA) increases. The SNR in unshielded environment is shown to be acceptable over a wide range of GA values when using the second-order gradiometers with a field balance ${\rm C}_{\rm B}=5\times 10^{-4}$ and a gradient balance ${\rm C}_{{\rm G}1}=5\times 10^{-3}$ or better. It is also shown that the optimal gradiometer baseline length strongly depends on the ambient noise level and the overall gradiometer balance. Shorter ($≪$80 mm) baselines are preferred only when using highly balanced gradiometers in a very high noise environments.