External magnetic field measuring method and static magnetic field amendment manner, magnetic detection means are installed in the vicinity

摘要

In order to nullify the adverse effect of an external magnetic field on a static magnetic field generated in an MRI system, small-size coils are used to generate a compensation magnetic field. Thus, the component of the static magnetic field to be applied to a magnetic sensor is canceled. The magnetic sensor can therefore detect the external magnetic field highly precisely. A correction current proportional to the external magnetic field detected highly precisely is fed to BO correction coils. Eventually, the external magnetic field that adversely affects the static magnetic field is canceled.