Calibration for a Multichannel Magnetic Sensor Array of a Magnetospinography System

A method for calibrating a multichannel superconducting quantum interference device (SQUID) magnetic sensor array of a magnetospinography (MSG) system is proposed. The MSG system detects weak magnetic fields generated by the neural activity of the spinal cord using the array of SQUID sensors. To calibrate 120 SQUID magnetic sensors, we employed an array of precisely machined circular coils to generate fundamental magnetic fields instead of employing Helmholtz coils, which are generally used for the calibration of magnetic sensors. The effective position, orientation, and sensitivity of each SQUID sensor were determined simultaneously by a parametric numerical optimization algorithm. These sensor parameters are essential for improving the accuracy of the magnetic source analysis. Using this method, we could calibrate the magnetic sensors even though they were installed in a non-transparent cryostat. In addition, the shifts from the designed position and orientation of the sensors as well as their variability were evaluated.