Graduate School of Engineering, University of Kyoto, Japan
Optically pumped atomic magnetometers (OPAMs) using alkali metal vapors contained in glass cells are capable of measuring extremely small magnetic fields. In recent years, OPAMs operating under spin-exchange relaxation-free (SERF) conditions have reached sensitivities comparable to and even surpassing those of superconducting quantum interference devices (SQUIDs). The most sensitive OPAM has sensitivity in the sub-femto tesla range. In addition, OPAMs have the intrinsic advantage of not requiring cryogenic cooling. Therefore, OPAMs are currently expected to overtake SQUIDs, and the possibilities for magnetoencephalography (MEG) and ultra-low field MRI have been demonstrated.
We have been developing super-sensitive OPAMs since 2006. After describing principles of the OPAM, we introduce our recent results of MEG and NMR/MRI measurements using a portable OPAM module to demonstrate its feasibility as a magnetic sensor towards innovative neuroimaging systems.
Finally, we describe some future research directions of the optical neuroimaging systems. For instance, we plan to detect neural magnetic field dependent (NMFD) changes in MR signals towards a new fMRI. To demonstrate the feasibility of the NMFD-fMRI, we present our results of both simulation and phantom studies using a spin-lock sequence, which is sensitive to oscillating magnetic fields.