Optical magnetometer array for fetal magnetocardiography

Abstract

We describe an array of spin-exchange-relaxation-free optical magnetometers designed for detection of fetal magnetocardiography (fMCG). The individual magnetometers are configured with a small volume with intense optical pumping, surrounded by a large pump-free region. Spin-polarized atoms that diffuse out of the optical pumping region precess in the ambient magnetic field and are detected by a probe laser. Four such magnetometers, at the corners of a 7 cm square, are configured for gradiometry by feeding back the output of one magnetometer to a field coil to null uniform magnetic field noise at frequencies up to 200 Hz. We present the first measurements of fMCG signals using an atomic magnetometer.

The atomic magnetometer: A new era in biomagnetism

“…6, the 4-channel system of Wyllie and coworkers was capable of recording high-quality MCG signals. This group also made the first fetal MCG recording (11). Signals were obtained from subjects as early as 21 weeks' gestation.…”

Optically pumped alkali magnetometers for biomedical applications

“…More recently, MCG detection by chip-scale ODMR magnetometers was compared to SQUID-based detection in the high performance magnetic shielding room at PTB-Berlin [9]. Spin-exchange relaxation free magnetometers [3] have been applied for recording magneto-encephalographic signals [10], and have recently produced human [11] and fetal [12] MCG signals of outstanding quality.…”

Magnetocardiography measurements with4He vector optically pumped magnetometers at room temperature

“…High sensitivity OPMs tested in the past are all based on a vapor of alkali atoms and exploit the optical and magnetic properties of paramagnetic alkali atoms. The most commonly used architectures of alkali OPM in the MCG field are Mx magnetometers (Bison, 2004) and the so-called Spin-Exchange Relaxation-Free (SERF) magnetometers (Wyllie et al, 2012), (Shah and Wakai, 2013). Both of them have only one sensitive axis.…”

“…In real clinical environment, demonstrated sensitivity of SERF prototypes is comprised between 10-100 fT/√Hz in the frequency range of interest for MCG (0.5-50 Hz). Fetal MCG measurements have recently been performed with an array of these alkali OPMs (Alem et al, 2015) (Wyllie, 2012).…”