Elektromagnetische Felder

8. Static magnetic fields like those used in medical imaging

• 8.1 What are the sources of static magnetic fields?
• 8.2 What possible health effects of static magnetic fields have been studied?

8.1 What are the sources of static magnetic fields?

MRI scanners use static magnetic fields
Credit: Kasuga Huang

A magnetic field is a force field created by a magnet or as a consequence of the movement of the charges (flow of electricity). The magnitude (intensity) of a magnetic field is usually measured in Tesla (T or mT).

Static magnetic fields do not vary over time, and as such do not have a frequency (0 Hz). Examples are the fields generated by a permanent magnet or the Earth’s magnetic field.

Man-made static magnetic fields are generated wherever electricity is used in the form of direct current (DC), such as in some rail and subway systems, in industrial processes such as aluminium production, the chloralkali process, and gas welding.

The number of artificial sources of such fields is limited, but there are rapid developments of new technologies producing static fields. The number of people with implanted metallic devices such as pacemakers that can be affected by static magnetic fields is also growing.

One prominent application of strong static magnetic fields is Magnetic Resonance Imaging that provides three-dimensional images of soft body tissue such as the brain and the spinal cord. This medical imaging technique uses very powerful permanent magnets, which can lead to high exposure levels both for patients and for operators. More...

8.2 What possible health effects of static magnetic fields have been studied?

Few epidemiological studies are available on the effects of static fields and the available evidence is not sufficient to draw any conclusion about potential health effects of exposure to static magnetic fields.

A large number of experimental studies have been carried out in an effort to detect biological effects of static magnetic fields.

Experimental data have established that static magnetic fields can exert small forces that result in changes in the orientation or position of biological molecules and cellular components – such as haemoglobin, rhodopsin, free radicals, and nitric oxide – according to their magnetic properties.

These effects are detectable at static magnetic field strengths of about 1 T, without known health consequences.

Static magnetic fields can also exert forces on, and affect the functioning of, implanted devices such as pacemakers.

Adequate data for proper risk assessment of static magnetic fields are almost totally lacking. The advent of new technology, and in particular MRI equipment, makes it a priority for research. More...