Objective To establish the reliability of fetal magnetocardiography as a method of measuring the Design A prospective study.Setting Wellcome Biomagnetism Unit, Southern General Hospital.Subjects One hundred and six low risk pregnant women at 20 to 42 weeks gestation. Main outcome measuresSuccess in obtaining QRS complexes, P waves and T waves. Correlation of time intervals with fetal outcome. Results The technique was acceptable to pregnant women. A QRS complex was successfully demonstrated in 68 (67 "/ o) of the unaveraged traces. Using off-line averaging techniques on these 68 cases, P waves were obtained in 75 YO and T waves in 72 YO. Although good quality traces were obtained throughout the range of gestational ages, in general it was more difficult below 28 weeks. QRS duration (R2 = 7 %, P = 002) demonstrated a positive linear correlation with increasing gestation. Of the 35 (51 YO) cases with umbilical vein pH analysis available, only one result was less than 7.2. No significant relation was found between measurements of the fetal waveforms and the pH results. Conclusion The technique of fetal magnetocardiography provides a significant advance in the technological field for the demonstration of QRS complexes and the full PQRST waveforms in gestations from 20 weeks onwards. With further technical improvements the clinical impact

We describe the design, fabrication, and performance of planar thin-film dc SQUID’s and planar gradiometers in which a dc SQUID is incorporated as a null detector. Each gradiometer was fabricated on a planar substrate and measured an off-diagonal component of changes in the magnetic field gradient. The gradiometer with the highest sensitivity had 127×33-mm loops that could be connected in parallel or in series: The sensitivities were 2.1×10−13 and 3.7×10−13 T m−1 Hz−1/2, respectively. The intrinsic balance of the gradiometers was about 100 ppm for fields parallel to their plane, and a balance of about 1 ppm could be achieved for fields perpendicular to their plane. When the series-loop gradiometer was rotated through 360° in the earth’s field, the output returned to its initial value to within an amount corresponding to a balance of 1 ppm. Possible improvements in sensitivity are discussed.

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Abstruct-Magnetic tensor gradiometry provides gradient components of true potential fields which enables unique depth estimates and improves analytic signal methods as well as providing a number of other advantages. A high temperature SQUID (HTS) gradiometer can provide measurements of the components of the earth's field tensor creating a new tool for mineral exploration. A successful comparison between a HTS SQUID gradiometer and a Cs-vapour gradiometer under survey conditions has been conducted. Both instruments were configured vertically. The HTS gradiometer measured the B, component of the gradient tensor, while the Cs-vapor gradiometer measured the vertical gradient of the total magnetic intensity. The HTS gradient measurement was the difference in output between two coaxial SQUID sensors. Effective noise levels achieved were 0.16-0.3 nT/m RMS, compared with 0.1-0.5 nT/m RMS for the Cs-vapor system. The SQUID noise was dominated by vibration with additional contributions from the multiplexed sampling between the SQUIDs. This paper reports on the system development, design issues, trial results and the implications for geophysical exploration.