An arrangement for association with an MRI and detecting presence of ferrous material and discriminating out far field magnetic disturbance. The arrangement includes a detector configured to monitor the magnetic field and includes an array of sensors arranged about the periphery of an opening in a spaced arrangement such that each sensor is associated with a different portion of the opening. Each of the sensors is configured to output a signal having a value indicative of the sensed magnetic field at the associated portion of the opening. The arrangement includes a corrector configured to correct each signal value from the change in response to the far field magnetic disturbance and to provide respective corrected signal values. The arrangement includes a processor configured to use the corrected signal values to determine a ferrous-indicating limit is exceeded and to provide a safety response that addresses the ferrous-indicating limit exceed condition.