Posts Tagged ‘Missile Effect’
• Implants and Electronics
• Missile Effect
Magnetic Resonance Imaging (MRI) uses powerful magnets and radio waves to produce detailed images of the body. While the magnets and radio waves are inherently safe, the powerful magnetic field can attract magnetic items and adversely affect electronic equipment.
The most dangerous hazard presented by the magnetic field is the Missile Effect. The Missile Effect occurs when magnetic items are quickly pulled into the bore (center) of the MR scanner. Standard, 1.5 Tesla MR scanners can attract items such as keys, paper clips or scissors at forty miles per hour. The more mass an item has, the stronger the attractive force on it will be. Heavier items, such as wheelchairs, can be pulled in just as quickly as smaller objects. The Missile Effect will not only damage equipment, but can fatally injure someone that is located between the item and the MR scanner.
The magnetic field poses other serious hazards if proper precautions are not taken. The magnet can twist and dislocate metallic components in electronics, power tools and surgically implanted medical devices. Aneurysm clips can be pulled or twisted from their original position, causing dangerous internal bleeding. Not all metallic objects are magnetic, but it is impossible to tell if an object is magnetic by sight alone. Testing is done on every item brought into the MR Suite to confirm its safety for that particular MR environment.
The magnetic field negatively affects electromagnetic devices brought into the MR suite. This poses a potentially fatal danger to those with surgically implanted medical devices. Pacemakers, neurostimulators, insulin pumps and intrathecal pumps can malfunction inside the MR scanner room.
While not as hazardous as the Missile Effect or the disruption of medical implants, the powerful magnet can also erase information from storage devices. Some common items that contain stored information are ID badges, credit cards, cell phones and flash drives.
Magnetic Resonance Imaging (MR) facilities and hospitals have specific rules and precautions for the areas surrounding the MR Suite. However, some general rules apply to all MR facilities and hospitals.
The most basic and important rule is to only bring MR-compatible equipment into the controlled access areas. All items should be tested and labeled before entering controlled access areas of the facility. The greatest type of hazard is bringing magnetic items into the MR Suite, which can be rapidly drawn into the magnet of the scanner – known as the Missile Effect.
Any hand tools or housekeeping supplies used in the magnet room must be made entirely of non-magnetic material such as brass, plastic, rubber or carbon fiber. Never bring power tools or mechanical cleaners, such as floor buffers, into the MR suite. All furniture in the controlled access areas of the MR suite must be completely free of metal, including screws or fasteners.
Surgically implanted medical devices can be negatively effected by the magnet. Pacemakers can malfunction near the MR scanner and aneurysm clips can be pulled out of place. The magnet can negatively affect any metallic fragments, bullets or shrapnel inside the body.
Minor emergencies in the MR suite can turn into more dangerous situations (situations that are more dangerous) when proper procedures are not followed. During an emergency inside the MR suite, three simple steps should be followed: 1) Evacuate the MR scanner room; 2) secure the room to prevent entry, and 3) alert a senior technologist or manager.
If the emergency involves the health of a person, such as cardiac arrest or a seizure, remove the person from the magnet room using MR-compatible equipment before administering medical treatment. Do not attempt to resuscitate or defibrillate anyone inside the MR scanner room.
If a fire occurs in the MR suite, evacuate the scanner room, secure the door, sound the alarm and call nine-one-one or your local fire department. Once the MR suite is evacuated, only properly trained personnel should attempt to contain the fire, using only MR tested and approved extinguishers. Untrained or unsupervised personnel should never enter the MR Suite. Not all firefighters or other first responders are aware of the hazardous magnetic field.
If the Missile Effect pulls an item into the scanner, a potential emergency situation may occur. Only after an object has completely settled on the magnet should a careful attempt be made to remove it. If the object can not be removed by two people without the aid of tools, an MRI service company should be called. The service company may have to ramp-down the MRI system, which slowly reduces the strength of the magnetic field.
A system quench rapidly shuts down the magnet, but is the last resort because it is both dangerous and can permanently damage the scanner. Unless it is a life-threatening situation, a quench must be authorized by the appropriate personnel. Evacuate the magnet room before a quench, or as soon as possible after the quench begins. Only trained and qualified personnel may enter the MR suite after a quench is initiated.
Pressure from released cryogen gas can force inward-swinging doors shut. If this occurs while inside the MR suite, break the glass or a window to release the pressure. Remember, the priorities in an emergency are to evacuate the MR suite, sound the alarm, secure the scanner room,and alert the proper personnel.