Abstract
Activation of the cardiac muscle is associated with ion transport through
the membrane of the cardiac cell. This gives rise to the strongest
electrophysiological signals in human body: the cardiograms. Segments of
the cardiogram are related to the contraction of the hearts chambers. In
fetal magnetocardiography, the magnetic field of a fetal heart is recorded
in the vicinity of the maternal abdomen. This magnetic field, however, is
extremely weak and can only be recorded by means of Superconducting
QUantum Interference Devices (SQUIDs). To reach the superconducting
state the SQUIDs are cooled to about - 270oC. Typically, fetal
magnetocardiograms are recorded inside magnetically shielded rooms in
order to reduce the influence of the environmental magnetic interference.
As an alternative to magnetic shielding, higher-order gradiometers can be
used. Ideally, a higher-order gradiometer is insensitive to the lower-order
gradients of the magnetic field that originate from relatively remote noise
sources. In practice, however, it is difficult to manufacture a gradiometer
such that its sensitivity to these lower-order gradients is eliminated
completely. The residual sensitivity to the lower-order gradients is
referred to as imbalance. Balancing a gradiometer reduces imbalance and,
thus, improves the environmental interference suppression. The objective
of the work presented in this thesis is to design a highly-balanced higherorder
gradiometer that enables measurements of fetal magnetocardiograms
in unshielded environment. This includes optimization of the geometry of
the gradiometer with respect to signal-to-noise ratio, design of a magnetic
coils set for gradiometer balancing and gradiometer balancing
experiments.
Original language | English |
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Qualification | Doctor of Philosophy |
Awarding Institution |
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Supervisors/Advisors |
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Award date | 6 Jun 2008 |
Place of Publication | Enschede |
Publisher | |
Print ISBNs | 978-90-365-2670-8 |
Publication status | Published - 6 Jun 2008 |