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Fetal magnetocardiography measurements with a multichannel microfabricated atomic magnetometer array

Published

Author(s)

Svenja A. Knappe, Orang Alem, Tilmann H. Sander, Rahul R. Mhaskar, John LeBlanc, Hari Eswaran, Uwe Steinhoff, Yoshio Okada, John E. Kitching, Lutz Trahms

Abstract

Following the rapid progress in the development of atomic magnetometer 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. The goal is the demonstration of multichannel measurements to obtain a spatial magnetic field mapping as a basis of biomagnetic applications. Here, an array of 25 microfabricated atomic magnetometers (υAM) was assembled using sensors with a footprint of 1 cm3. The individual sensors were inserted into three flexible belt-shaped holders and connected to their respective light sources and electronics, which reside outside the magnetically shielded room, by long optical and electrical cables. With this setup the fetal magnetocardiogram (fMCG) of a pregnant woman was measured by placing two sensor belts over the abdomen and one belt over the chest. The preprocessing of the measured data from the υAM array consists of a demodulation step (lock-in technique), since the directional readout of the sensors relies on a field modulation technique. The fMCG recorded over the abdomen is usually dominated by contributions from the maternal MCG (mMCG) as the maternal heart generates a much stronger signal than the fetal heart. This is well known from fMCG recordings using superconducting quantum interference devices (SQUIDs) where signal processing methods have to be applied to obtain the pure fMCG. Here, two methods, orthogonal projection (OP) and independent component analysis (ICA), are used to suppress the mMCG. The identification of mMCG is facilitated by analyzing the channels over the chest. Results from the two independently applied methods agree well as the fMCG field map, extracted by ICA, matches the average fMCG R peak map after OP. In a further step, the fetal heart rate variability was extracted from the fMCG and the result is consistent with published data of SQUID fMCG. We found that υAMs are capable of co
Citation
Physics in Medicine and Biology
Volume
60
Issue
12

Keywords

atomic magnetometer, MEMS, microfabrication, biomagnetics, magnetocardiography, MCG
Created June 3, 2015, Updated November 10, 2018