MRI Units: Medical Technology that Should Attract Your Attention
STRATEGY & TACTICS
Emergencies involving magnetic resonance imaging units require unusual tactics and procedures.
(Photos by Robert Drennen.)
MORE AND MORE hospitals and healthcare facilities have begun using magnetic resonance imaging (MRI) as a diagnostic tool. Magnetic resonance is considered revolutionary in that it involves no pain or radiation: It provides a three-dimensional view of soft tissues within the body’s soft tissues—tumors in the brain, muscles, and tendons, for example. Soft tissues create little or no shadows so they cannot be detected by conventional X-ray methods.
In 1982 only six MRI units were in operation in the United States. In 1988 that figure rose to more than 600. Located in main hospital buildings, adjoining buildings, or trailers parked in adjacent lots, they pose a unique problem to firefighters: Their strong magnetic field and their ability to attract ferromagnetic items with such strength that they can become airborne can result in serious injury or death.
In an accident at the University of Cincinnati Medical Center in 1986, a technician was almost killed while installing an MRI unit in a converted semitrailer for use as a mobile diagnostic center. While he lay inside the heart of the machine, two steel tines weighing about 80 pounds each, attracted by the magnetic field, flew off an approaching forklift and knocked him 15 feet, causing him serious injury. The magnetic field also complicated efforts to help the victim. A doctor had to remove his stethoscope before he could approach the victim, and when a paramedic tried to cut off the injured man’s pants, the scissors flew out of his hand.
MRI technology combines the use of radio frequency transmissions with the unit’s ability to generate and sustain high and uniform magnetic fields. A patient lies on a flat, motorized platform, which is located in the “scan room.” The platform carries the patient through a cylinder approximately three feet wide and six feet long. The magnetic field exists within the entire scan room.
The magnetic field inside the cylinder causes the hydrogen atoms within the body to align. A radio frequency signal is then transmitted to upset the formation. When the signal is turned off, the hydrogen atoms return to their formation. By measuring the speed and volume with which the atoms return, the computer makes an assessment and displays a diagnostic image on a monitor.
The magnetic field is sustained with a superconductive magnet, which is immersed in a liquid helium bath and encased in an aluminum holding tank of liquid nitrogen. The liquid nitrogen and helium are usually stored in nonmagnetic dewars within the building. The scan room contains the magnet and is shielded with copper sheathing to protect the unit from outside radio frequency transmissions and to contain the magnetic field.
It is important to realize that radio frequency shielding prevents fire department radio communications with personnel in the scan room. With superconductors, once the magnetic field has been established in the conductor no further power needs to be supplied. Shutting down the electric supply to the scan room does not shut down the unit.
QUENCHING THE MAGNET
The only way to shut down the MRI unit is to “quench” the magnet. In limited cases where human life is in jeopardy, quenching the magnet may be necessary. This process involves eliminating superconductivity by releasing helium and nitrogen from the unit through vents to the exterior. Quenching may take between two and five minutes, and it is possible that some gases may escape into the scan room, causing an oxygen-deficient atmosphere.
(Photo by Robert Drennen.)
Quenching should be done by the attending technician, who activates the emergency quench valve. However, if the technician is injured or unavailable, fire department personnel should be familiar enough with this operation to carry it out.
Quenching the unit is an expensive proposition and should only be done for life-safety reasons. A quench can cost the hospital in excess of S 10,000 for the loss of nitrogen and helium, approximately S 16,000 for every day the unit is unavailable for patients, and the salaries of the hospital technicians who would normally operate the unit. What can’t be calculated is the impact on the patients who need the services of the machine but who cannot receive medical diagnoses because the unit is down.
Technicians also can “rhine down” the unit. This is a shutdown process that recovers most of the helium and nitrogen for subsequent use. ,It may take between two and four hours. This process is impractical for immediate rescue in the scan room but is appropriate when the unit is threatened by fire extension from another area of the building or when salvage operations in the room may become necessary.
The following are considerations firefighters should take into account when responding to a call in an MRI unit:
- Do not enter the scan room with any ferromagnetic items, such as hand tools, SCBA, extrication equipment, and jewelry. Also, remove all credit cards from your pockets, since these will become activated by the magnetic field.
- Control the activity of personnel so no one strays into the scan room. Assemble emergency personnel at safe standby locations and assign as needed.
- Consult with technicians who are operating the machine before implementing a plan of action.
- Remember, you cannot communicate with personnel operating in the scan room via portable radio. Hand signals must be used.
- Avoid opening the walls and ceiling of the scan room, if possible, because of the damage to the copper sheathing.
- Do not use dry chemical extinguishing agents because of damage to the unit. Halon is recommended by manufacturers and many scan rooms are protected with Halon automatic discharge systems. Generally, there are few combustibles in the scan room. Should water application be necessary, electrical power to the area must be shut down and the unit quenched beforehand. If there is no life hazard in the scan room, an immediate quench probably will not be necessary. However, in an extended fire operation in which the scan room is a threatened exposure, it may be necessary to quench the unit.
MRI units represent the latest technological advancement for medical diagnosis, and their use is increasing steadily. As usual, a fire department’s best action is to have a preplan in place. Familiarize yourself with your local hospitals and healthcare facilities, and know where their MRI units are located. Knowing how to handle incidents involving MRls will help you to keep your head—and your tools—during a rescue.