Method and apparatus for ferrous object and/or magnetic field detection for mri safety

The present application is a divisional of U.S. application Ser. No. 11/635,417, filed Dec. 7, 2006, which claims the benefit of U.S. Application Ser. No. 60/748,635, filed Dec. 8, 2005, both of which are hereby incorporated by reference herein in there entirety, including any figures, tables, or drawings.

Magnetic resonance imaging (MRI) technology is used for diagnostic purposes in hospitals and medical research centers. Through the use of two magnetic fields, one static and one time-variant, MRI technicians can obtain very detailed, high resolution images of the human body.

Magnets, such as superconducting magnets, permanent magnets, and electromagnetic magnets, used in applications such as magnetic resonance imaging produce stray static magnetic fields. The magnitude of these stray fields can vary significantly depending on the distance relative to the center of the magnet. The earth produces a magnetic field slightly less than one Gauss, but fields above 5 Gauss can cause electronic devices such as pacemakers to malfunction. In addition, the magnetic field strength of an MRI magnet is often large enough to turn ferrous objects into projectiles and cause electrical devices and magnetic strips to malfunction.

The static magnetic field can extend several meters outwards from an MRI machine cavity at strengths of up to 3 Tesla, or about 3×10⁵ times the strength of Earth\'s magnetic field. Objects with significant ferromagnetic content in the vicinity of an MRI machine can be attracted to this field and accelerated at high speeds toward the cavity, posing a significant risk of damage to the machine and the threat of injury to patients undergoing scanning. The removal of foreign ferromagnetic objects from an MRI cavity can also require the machine to be shut down completely (quenched), a time-consuming and expensive process.

Others have attempted to provide a safer environment for MRI\'s to be performed. U.S. Patent Application Publication No. US 2004/0135687 A1 teaches a ferromagnetic object detector that measures the change in a known magnetic field when a ferrous object passes through. The detector incorporates a proximity sensor to trigger the magnetic field detector, reducing the number of false alarms. U.S. Patent Application Publication No. US 2003/0171669 A1 teaches an MRI Protector that incorporates an array of Hall sensors around an entrance to an MRI room.

Embodiments of the subject invention relate to a method and apparatus for ferrous object and/or magnetic field detection. Embodiments can improve magnetic resonance imaging (MRI) safety and increase the safety of MRI facilities. Embodiments of the subject system can detect a given magnetic field strength around a magnetic resonance imaging (MRI) machine and alert users to the field\'s presence. In an embodiment, the magnetic field warning system can rely on a single badge that warns its user. In another embodiment, a badge with an RFID system can be utilized. The RFID system can turn the badge on when it enters the MRI room and off when it leaves the MRI room. In another embodiment, a badge with a rechargeable battery and charger can be utilized with or without an RFID tag. The subject badges or other detection devices can be worn by a person, located on or near a ferrous object, embedded in clothing, or located in other positions convenient to a user. Examples of ferrous objects include: fire extinguishers, wheelchairs, and crash carts.