Magnetoneurography: theory and application to peripheral nerve disorders.

Magnetoneurography (MNG) is a non-invasive method to trace and visualize three-dimensionally the propagation path of compound action currents (CAC) along peripheral nerves. The basic physical and physiological principle is the mapping of extremely weak magnetic fields generated by the intraaxonal longitudinal ion flows of evoked nerval CAC using SQUID sensors (Superconducting Quantum Interference Devices). During recent years, MNG protocols have been established which allow for a non-invasive spatiotemporal tracing of impulse propagation along peripheral nerves in humans and in particular along proximal nerve segments in a clinical setting. Thereby, the three-dimensional path, the local nerve conduction velocity, the length and strength of the CAC de- and repolarization phase have been reconstructed. First recordings in patients demonstrated that the method is sensitive enough to detect and to localize nerve conduction anomalities along nerve roots, as, e.g. caused by lumbosacral disc herniation. This review on MNG will focus on those studies which provide data from humans and thereby reveal perspectives for its future clinical applications.