Fetal magnetocardiography measurements with an array of microfabricated optically pumped magnetometers

Abstract

Following the rapid progress in the development of optically pumped magnetometer (OPM) technology for the measurement of magnetic fields in the femtotesla range, a successful assembly of individual sensors into an array of nearly identical sensors is within reach. Here, 25 microfabricated OPMs with footprints of 1 cm(3) were assembled into a conformal array. The individual sensors were inserted into three flexible belt-shaped holders and connected to their respective light sources and electronics, which reside outside a magnetically shielded room, through long optical and electrical cables. With this setup the fetal magnetocardiogram of a pregnant woman was measured by placing two sensor belts over her abdomen and one belt over her chest. The fetal magnetocardiogram recorded over the abdomen is usually dominated by contributions from the maternal magnetocardiogram, since the maternal heart generates a much stronger signal than the fetal heart. Therefore, signal processing methods have to be applied to obtain the pure fetal magnetocardiogram: orthogonal projection and independent component analysis. The resulting spatial distributions of fetal cardiac activity are in good agreement with each other. In a further exemplary step, the fetal heart rate was extracted from the fetal magnetocardiogram. Its variability suggests fetal activity. We conclude that microfabricated optically pumped magnetometers operating at room temperature are capable of complementing or in the future even replacing superconducting sensors for fetal magnetocardiography measurements.

Measuring MEG closer to the brain: Performance of on-scalp sensor arrays

“…In practice, the thermal insulation needed between the outside surface of the sensor and the heated vapor cell imposes a lower limit on this distance. Alem and colleagues (2015) have manufactured OPMs with small vapor cells of (1.5 mm) 3 and with a distance of 4.5 mm from the center of the cell to the outer surface of the sensor housing. OPMs by QuSpin Inc. (Louisville, USA) contain vapor cells of (3 mm) 3 and exhibit a distance less than 6 mm from the center to the surface of the sensor.…”

Chip-scale atomic devices

“…210 Advances in sensor design and engineering now make it possible to fabricate moderate numbers of chip-scale magnetic sensors with a high degree of uniformity from sensor to sensor in terms of operating power and sensitivity. 221,222 An example of such a sensor is shown in Fig. 44.…”

“…The ability to measure epileptic discharges is therefore an important demonstration for any new magnetometer technology and such measurements were carried out in mice. 242 The development of flexible, reconfigurable chip-scale atomic magnetometer arrays 222 has enabled the detection of fetal magnetocardiographic signals with reduced interference from the heartbeat of the mother. 222 A photograph of the array used for MEG imaging is shown in Fig.…”

Magnetic field imaging with microfabricated optically-pumped magnetometers

“…Due to the small size of the sensor heads, they can be positioned very close to the area of interest, which can result in large signal strengths. The same sensor heads were used for magnetocardiography in a related publication [9]. Previously, a multichannel image of a coil has been evaluated with a very large OPM consisting of a single cell of volume (5 cm) 3 , which restricted the relative position of the array channels to within that volume [10].…”