Realistic Neural Current Model for Developing a Phantom for the Evaluation of Spinal Cord Biomagnetic Measurement

Spinal cord functional imaging by magnetospinography (MSG) is a noninvasive diagnostic method for spinal cord diseases. However, the accuracy and spatial resolution of lesion localization by MSG have barely been evaluated in detail thus far. We propose a realistic neural current model to become part of a spinal cord phantom for evaluation of MSG. The realistic neural current model is composed of a catheter with four electrodes dipped in saline water. The neural current distribution accompanied with action potential propagating along the spinal cord, which is composed of intracellular current in the axons and extracellular volume current, is properly emulated. To show the effectiveness of the developed model, the distribution of the magnetic field evoked by the emulated neural current was recorded by an MSG system with a superconducting quantum interference device (SQUID) vector gradiometric magnetometer array. To evaluate the neural current model, the results of the magnetic field recording were compared with the numerical simulation using the boundary element method and Geselowitz equations. Goodness of fit between the measurement and the simulation was more than 95%. It revealed that the neural current model would be sufficiently effective for the evaluation of MSG systems.