Magnetoneurography

In the human body, sensations are mediated by impulse propagation along peripheral nerves through the spine to the brain. Blockades or irritations of nerves affected, e. g., by intervertebral disc herniaton, may lead to sensory loss or palsy. The localisation of the damaged area is of great importance for diagnosis and therapy.

The extremely weak biomagnetic fields associated with the electrical currents in the nerves which mediate a sensation and its strength ask for sensors of extremely high sensitivity. The most sensitive magnetic field sensors based on SQUIDs (superconducting quantum interference devices) worldwide are developed by PTB. They are used for contactless multichannel measurements of such biomagnetic fields.

Recently, PTB developed the technique of clinical magnetoneurography in cooperation with neurologists of the Benjamin Franklin School of Medicine of the Free University Berlin. This technique allows to trace the path of an impulse along the nerves from an arm or leg to the spine with high temporal and spatial precision. Detection of the weak signals is a true challenge because they are hidden in magnetic fields of the earth, technical devices, or the human heart that are up to thousand million times stronger. Therefore, sophisticated methods for shielding and signal processing had to be developed and implemented to enable the measurement of magnetic signals produced by nerve currents. Once the spatial and temporal magnetic field distribution is recorded, mathematical models allow to reconstruct the way taken by the underlying stimulus.

The first visualisation of the impulse block of a leg nerve in a patient caused by a herniated intervertebral disc was recently accomplished and opens very attractive future possibilities for clinical diagnosis and therapy.