The human body is controlled by electrical impulses in, for
example, the brain, the heart and nervous system. These electrical signals
create tiny magnetic fields, which doctors could use to diagnose various
diseases, for example diseases of the brain or heart problems in young
foetuses. Researchers from the Niels Bohr Institute have now succeeded in
developing a method for extremely precise measurements of such ultra-small
magnetic fields with an optical magnetic field sensor. The results are
published in the scientific journal, Scientific Reports.
Small magnetic fields from the human
body can usually only be picked up by very sensitive superconducting magnetic
field sensors that have to be cooled by liquid helium to near absolute zero
(which is minus 273 degrees Celsius). But now researchers from the Niels Bohr
Institute at the University of Copenhagen have developed a much cheaper and
more practical optical magnetic field sensor that even works at room
temperature or at body temperature.
"The optical magnetic field
sensor is based on a gas of caesium atoms in a small glass
container. Each caesium atom is equivalent to a small bar magnet,
which is affected by external magnetic fields. The atoms and thus the magnetic
field are picked up using laser light. The method is based on quantum optics
and atomic physics and can be used to measure extremely small magnetic fields,"
explains Kasper Jensen, assistant professor in the Center for Quantum Optics,
Quantop at the Niels Bohr Institute at the University of Copenhagen.
The researchers at the Niels Bohr
Institute have been developing the sensitive magnetic field sensor for several
years in the Quantum research group laboratories.
The magnetic field sensor itself
consists of a glass container, which has a channel that is approximately 1cm
long and 1 mm wide. At the bottom of the glass container is caesium metal.
Caesium evaporates into gas at room temperature and the gas atoms rise up into
the small channel in the sensor head. Each caesium atom rotates around itself
and the axis is like a tiny bar magnet. Now the sensor is held close to a
nerve, which emits an electrical nerve pulse. The electrical pulse has a
magnetic field that causes a change in the tilt of the axes of the caesium
atoms and by sending a laser beam through the gas, you can read the ultra-small
magnetic fields of the nerve signals.
The laboratory tests, which were
carried out in collaboration with researchers from the Faculty of Health and
Medical Sciences, have shown that you can use the magnetic field sensor to
detect the magnetic fields from the electrical impulses from the nervous
system. The tests were done on the sciatic nerve from a frog, which in many
ways resemble the nerves in the human body. For practical reasons, the nerve was
removed from the frog before the tests, but it is also possible to pick up
electrical impulses from live frogs or from humans.
The advantage of the optical sensor
is precisely that the magnetic fields and electrical
impulses can be safely and easily picked up at a distance of a few
millimetres or centimetres – without the sensor actually coming into contact
with the body.
"We expect that the sensor will
be used for special medical examinations, where it is important for the sensor
not to be directly in contact with the body, for example, for diagnosing heart
problems in tiny foetuses. Here the magnetic
field sensor is placed on the mother's abdomen and you can easily
and safely detect the heartbeat of the foetus and you will be able to diagnose
any heart problems at an early stage so that the foetus can get the right
treatment quickly," explains Eugene Polzik, professor and head of Quantop
at the Niels Bohr Institute.
Eugene Polzik explains that you can
calculate the speed at which the nerve impulses are moving from the measured
signals. There are a large number of diseases where the nerves are damaged, for
example, multiple scleroses, where the nerve impulses move more slowly than in
people who are not ill. Other issues could, for example, be a number of eye
diseases where you will be able to make the diagnosis without having to put
electrodes on the eye or Alzheimer's, where you will be able to measure the
electrical signals in specific nerve pathways.
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