Magnetoneurography as a novel functional imaging technique for the ulnar nerve at the elbow

Abstract

Objective: To visualize the neural activity of the ulnar nerve at the elbow using magnetoneurography (MNG).

Methods: Subjects were asymptomatic volunteers (eight men and one woman; age, 26-53 years) and a male patient with cubital tunnel syndrome (age, 54 years). The ulnar nerve was electrically stimulated at the left wrist and evoked magnetic fields were recorded by a 132-channel biomagnetometer system with a superconducting quantum interference device at the elbow. Evoked potentials were also recorded and their correspondence to the evoked magnetic fields was evaluated in healthy participants.

Results: Evoked magnetic fields were successfully recorded by MNG, and computationally reconstructed currents were able to visualize the neural activity of the ulnar nerve at the elbow. In the affected arm of the patient, reconstructed intra-axonal and inflow currents attenuated and decelerated around the elbow. Latencies of reconstructed currents and evoked potentials were correspondent within an error of 0.4 ms in asymptomatic participants.

Conclusions: Neural activity in the ulnar nerve can be visualized by MNG, which may be a novel functional imaging technique for ulnar neuropathy at the elbow, including cubital tunnel syndrome.

Significance: MNG permits visualization of evoked currents in the ulnar nerve at the cubital tunnel.

Keywords: Evoked magnetic field; Evoked potential; Magnetoneurography; Magnetospinography; Recursively applied null-steering; Superconducting quantum interference device.