Patent ID: 7489128

Claim:
A protection arrangement for association with an operable MRI apparatus located within a room that has an access opening, the MRI apparatus providing a residual magnetic field that extends to a location of the opening, the arrangement including: a detector for passively monitoring the residual magnetic field at the location of the opening, the detector includes an array of passive magnetic field sensors arranged about the periphery of the opening in a spaced arrangement such that each sensor is associated with a different portion of the access opening, the field changing in response to a presence of ferrous material at the opening, each of the sensors including means for outputting a signal indicative of the ferrous material responsive change in the magnetic field at the associated portion of the access opening; and means for receiving the change indicative signals, for determining whether the change indicated by at least one of the change indicative signals exceeds a limit and for providing a safety response that addresses the condition of ferrous material at the opening of the room within which the MRI apparatus is located upon determination of at least one threshold being exceeded.