Conductive neuromagnetic fields in the lumbar spinal canal

ObjectiveTo measure neuromagnetic evoked fields in the lumbar spinal canal.MethodsUsing a newly developed superconducting quantum interference device (SQUID) fluxmeter, neuromagnetic fields of 5 healthy male volunteers were measured at the surface of the lower back after stimulation of the tibial nerves at the ankles. For validation, we inserted a catheter-type electrode percutaneously in the lumbar epidural space in 2 of the subjects and measured cauda equina action potentials after tibial nerve stimulation.ResultsNeuromagnetic fields propagating from the intervertebral foramina into the spinal canal were measured, and the latencies of the magnetic fields corresponded largely with those of the cauda equina action potentials.ConclusionsWe successfully measured ascending neuromagnetic fields originating at the nerve root and the cauda equina with high spatial resolution. Future studies will determine whether neuromagnetic field measurement of the lumbar spine can be a useful diagnostic method for the identification of the disordered site in spinal nerves.SignificanceWe successfully measured neuromagnetic fields in the lumbar spinal canal, which have previously been difficult to verify. Future studies will determine whether neuromagnetic field measurement of the lumbar spine can be a useful diagnostic method for identifying disorders of spinal nerves.

► We used a superconducting quantum interference device fluxmeter developed for use with the spine to measure propagating neuromagnetic fields at the surface of the lower back after stimulation of tibial nerves at the ankle.
► We simultaneously measured cauda equina action potentials with an epidural catheter-type electrode to validate the accuracy of the neuromagnetic field measurements.
► This method provides a noninvasive functional examination tool for lumbar spine disease.