Mobile reference sensors for reducing magnetic noise originating from a cryocooler of an MEG System

Abstract

The authors have developed a noise reduction signal processing method, named a mobile-reference sensor method, for biomagnetic measurement systems. In this study, we proposed employing a vibration meter (VM) and a fluxgate magnetometer (FGM) as reference sensors to detect the noise generated by the cryocooler installed near a magnetoencephalography (MEG).We placed an MEG cryostat and a helium-recycling system composed of a pulse tube cryocooler inside a magnetically shielded room and connected them by a transfer tube. We measured the vibration and the magnetic noise during operating the cryocooler using the MEG sensors, the VM and the FGM with various positions. The coherence values between the MEG sensors and the mobile reference sensors were maximized when the VM and FGM were put on the top and the side of the cryocooler, respectively. The obtained results suggested that the possibility to reduce the cryocooler-related magnetic noise from the recorded MEG data.