Quantum sensors have the potential to significantly improve medical diagnostics. In a joint research project with the University Hospital of the Friedrich Schiller University of Jena, a measuring device was developed to examine the well-being of foetuses in the last weeks of pregnancy. The meaningful goal of the work is to establish the magnetic measurement method as an additional clinical diagnostic for gynaecology and obstetrics and thus to improve medical care for the benefit of expectant mothers and their offspring.
Objective
Supracon joined forces with the developers of the Leibniz-Institute of Photonic Technology(IPHT) and the Grönemeyer Institute for Microtherapy to create an unique device for prenatal diagnostics.
The aim is to develop a non-invasive measurement system for heart function diagnosis of fetuses in the womb using highly sensitive SQUID sensors. SQUID systems are used in medical diagnostics to measure and analyse very weak local magnetic fields of living organisms and human organs. The measurement method allows, for example, a functional tomographic recording of cardiac muscle activity with the highest temporal resolution and is completely safe and painless for the patient.
Signal of fetus at the 36. week of gestation measured in unshielded environment, top: mother and fetus signal, middle: mother signal, bottom: fetus signal
The routine screening of fetuses is currently being conducted primarily by Cardiotocography (CTG) and Doppler-ultrasound in clinical practice. Differentiated clinical diagnostic value of these methods has limits especially when it comes to precise analysis of heart rate variability and the assessment of fetal arrhythmia. Electrocardiography (ECG) cannot be routinely applied because the electrically isolating Vernix caseosa around the fetus substantially attenuates the signals.
The magnetic fields produced by the fetal heart however propagate unhindered. Our measuring devices ultimate sensitivity allows the detection of biomagnetic signals from the 2. trimester of pregnancy onwards.
Signal of a pregnant woman and her foetus in the 36th week of pregnancy, measured in unshielded environment, top: Mother and foetus signal, middle: Mother's signal, bottom: Fetal signal
Routine monitoring of the foetus today is primarily carried out with cardiotocography (CTG) and Doppler ultrasound. Although differentiated clinical-diagnostic statements are possible on the basis of these procedures, a precise calculation of heart rate variability as well as the assessment of foetal arrhythmias from an electrophysiological point of view is only possible to a limited extent.
Electrocardiography (ECG) cannot be used routinely due to the isolating effects of the Vernix caseosa.
However, since the magnetic fields generated by the foetal heart can spread unhindered, it is possible with sensitive biomagnetic measuring systems to register the ECG (an ECG-like signal) from the 2nd trimester onwards and to evaluate it.
Heart rate analysis shown as R-R interval in a foetus at 28 weeks gestation.
FVC measurements are of particular diagnostic importance for the identification and classification of foetal arrhythmic activity.
Furthermore, the high temporal resolution of the FVC signal allows an accurate and highly differentiated analysis of fetal heart rate variability. The latter has a high diagnostic value in the assessment of fetal condition and acute fetal stress.
Furthermore, the morphology of the PQRST course can be used to make statements about growth retardation or possibly ST changes in the context of ischaemia.
Results
In the project and also through publications by the scientific cooperation partners, it could be shown that FVC can be used to expand conventional ultrasound-based technology to include the analysis of fetal beat-to-beat variability and arrhythmia diagnostics. It provides a convincingly demonstrated alternative to monitor the critical phase of fetal autonomic nervous system (ANS) development. The fMCG allows electrophysiological recording of cardiac excitation throughout the second half of pregnancy (van Leeuwen et al. 1999, van Leeuwen et al. 2004). The method is largely independent of tissue conductivity, non-invasive because it is passive, and contact-free. A top innovation is the implementation and validation of the fMCG in a magnetically unshielded environment directly in the hospital. The fMCG system is to be transferred from basic research to the clinic and thus opened up to a broader spectrum of obstetric patients, especially those with risks and under inpatient supervision. This is associated with an expected improvement in patient compliance due to the smaller size of the measuring device and the elimination of transport. The unshielded fMCG has the potential to expand the existing possibilities of fetal condition monitoring in an exclusive way during a critical phase for fetal development.
Performance
Our fMCG system is based on integrated first-order planar gradiometers. This type of gradiometers provides very high common mode rejection of magnetic noise from distance sources.
The gradiometers are manufactured in standard all-refractory Nb/Al-O/Nb technology developed at IPHT Jena. They are waterproof and robust against thermal cycling. Standard silicon 4-inch wafers are used.
The gradiometer has two pick-up loops connected in series. The main gradiometer parameters are shown in Table I. A more detailed description of the SQUID and gradiometers is given in reference [4].
Main gradiometer parameters
| Chip size: | 6 cm × 2 cm |
| Size of one pick-up loop: | 2 cm × 2 cm |
| Size of Josephson junction: | 3.2 μm × 3.2 μm |
| SQUID inductance: | 350 pH |
| Pickup loop inductance: | 250 nH |
| Effective volume: | 300 mm3 |
| Effective pick-up area: | 7.5 mm2 |
| Baseline: | 4 cm |
Typically, the gradiometer has an intrinsic noise resolution better than 2 fT/ √Hz and common mode rejection more than 5000.