Multichannel SQUID system for detecting fetal magnetocardiograms

A nine-channel SQUID magnetometer system is developed to detect weak magnetic fields generated by fetal cardiac activity. The nine 20-mm-diameter axial first-order gradiometers are mounted at intervals of 30 mm. A baseline length of 60 mm is applied to the pickup coil to measure the weak magnetic field from a fetal heart in a deep position. The SQUID is operated with a flux-locked loop (FLL) circuit and the FLL output is recorded at 1 kHz by a computer. Fetal magneto-cardiograms (FMCG) were measured for 109 fetuses of 20 to 39 weeks' gestation. In most cases, maternal MCG interference was negligible. R-wave peaks were detected in 81% of all subjects. The results of FMCG measurements and Fourier analysis of fetal the R-R interval are shown in this paper.