Fetal Magnetocardiography

Fetal magnetocardiography is a non-invasive method to study the fetal heart: the patient (i.e., the mother) is not even touched. A fetal magnetocardiogram (MCG) is the registration of a component of the magnetic field generated by the electrical activity of the fetal heart. Usually the component of the magnetic field that is perpendicular to the maternal abdomen is measured. Fetal MCGs show the typical features that are found in ECGs of adults (i.e. a P-wave, QRS-complex and T-wave). To enable the discrimination between pathological and healthy fetuses, values of the duration of these waveforms are collected in several research groups. These durations can be used as a reference. Measurements show that MCGs of fetuses with severe congenital heart disease have an abnormal shape. Hence, fetal MCGs may be of help in the early intra-uterine detection of congenital heart anomalies and the progress of the disease. Fetal magnetocardiography can also be used to classify fetal arrhythmias.

The fetal MCG is a very weak signal (about 10−13 tesla) compared with fields that are present in a hospital. The Earth’s magnetic field, for example, is about 5 × 10−5 tesla. The only magnetic field sensor that is sensitive enough to measure fetal MCGs is a SQUID. This sensor has to be cooled in liquid helium. The vessel containing the helium and the sensor is positioned near the maternal abdomen. At present, fetal MCGs are measured within magnetically shielded rooms in order to avoid disturbing fields. Signal processing techniques, such as filtering and averaging, are used to enhance the signal-to-noise ratio. The electrical activity in the heart gives rise to currents in the fetus and maternal abdomen. These currents also contribute to the fetal MCG. In order to estimate this influence, simulations are carried out and discussed in the last section of this chapter on fetal MCG.