Magnetic Resonance Imaging (MRI) Magnetic resonance imaging (MRI) is a technology that uses a strong magnetic force, radiofrequency waves and a computer to create images of the body. MRI targets the protons in the nuclei of hydrogen atoms. (Since the body contains a large amount of water - or H2O, there is an abundant amount of hydrogen in the tissues.) When the magnetic field is turned on, the hydrogen protons become excited and "spin." Next, the magnetic force is interrupted. As the protons "relax" they emit a faint radio signal, which is detected by a receiver in the MRI unit. A computer measures the strength of the signals and creates an image from that information.

MRI is one of several different diagnostic imaging techniques. The standard imaging procedure, X-rays, uses radiation to produce images of dense structures in the body, like bone. MRI, on the other hand, is used to take pictures of soft tissue and blood. It doesn't expose the patient to radiation and may be especially important for imaging areas like the heart, blood vessels, lungs, liver, kidneys and bladder. MRI may also be useful for detecting or evaluating tumors.

MRI Safety Concerns According to the Institute for Magnetic Resonance Safety, Education, and Research, about 10 million people undergo an MRI annually. So far, more than 150 million of the procedures have been done. While MRI is proved to be a safe and effective diagnostic procedure, it is associated with some risk.

An important safety concern with MRI is the machine's ability to attract metal objects. Today's MRI machines are faster, have stronger magnetic fields and more powerful radiofrequency transmission coils. The typical MRI is 30,000 times more powerful than the earth's gravitational field. So any metal objects in the room can be pulled into the MRI unit.

In 2001, a six-year-old boy undergoing an MRI died when a steel oxygen tank was suddenly pulled into the patient chamber at high speed. The oxygen tank had been brought into the room during the scan and was pulled out of the doctor's hands. The young child suffered a skull fracture and brain hemorrhage, and died two days later. Since then, healthcare workers have reported other objects being inadvertently caught in the pull of the MRI unit, such as a tool box, vacuum cleaner, defibrillator and wheelchair. Even small objects can be dangerous. Experts say a metal wrench pulled from just two feet away from an MRI unit will hit the machine at a speed of about 30 to 40 miles per hour.

The risks associated with MRI aren't limited to metal objects in the room. Any magnetic-susceptible metal in or on the body can also be affected by the magnetic force from an MRI. Metallic objects in the body, like surgical wires, clips and pacemakers can be pulled into the magnetic field. Serious injury or death can occur if the implant is dislodged (as in an aneurysm clip in the brain) or malfunctions (interference with a pacemaker). Metal can also heat during an MRI scan and cause severe burns in the surrounding area. Jewelry, electrode leads and foil-backed drug patches have been reported to cause serious burns during an MRI scan. Even metal fragments in tattoo ink or cosmetics can cause burns.

Safety Precautions Most cases of MRI-related injury occur because safety guidelines were not followed or staff had outdated information. One important misunderstanding is the impression that an MRI unit is safe when not in use. However, an MRI is never turned off, except for maintenance (suddenly shutting the unit down can damage the very costly magnet). So even though there may not be anyone in the scanner, the machine still has a very strong magnetic force. Therefore, all personnel who may have access to the room with the MRI unit, including housekeeping personnel, security and other healthcare providers, should be educated about potential dangers.

Patients who are having an MRI should be prescreened for the presence of any metal objects or accidental exposure to metal fragments (at least one patient sustained a serious eye injury due to metallic fragments lodged in the eye). On the day of the scan, the patient should be screened again. Hearing aids, jewelry, hairpins, keys, clothing with metal zippers or closures and metal belt buckles should be removed prior to the scan.

Health experts have develop a list of safety questions for consumers to ask before undergoing an MRI:

1. Is the facility and the technologist(s) accredited? The American College of Radiology (ACR) has issued guidelines for MRI facilities and personnel. Certification is not a guarantee of safety. However, facilities that take the time to achieve certification may be more likely to take safety issues seriously and adhere to safety guidelines.

2. Does the facility follow the ACRs 4-zone safety and screening procedures? The ACR has divided MRI facilities into four safety zones, each with separate screening. Zone I is the area outside the building. Zone II is the area inside the facility. Zone III is the area just outside the magnet room. Even though zone III is outside of the immediate scanning area, there is still a potential for magnetic fields to interact with susceptible devices. Zone IV is the magnet room, where the risk of dangers is the highest.

3. Is there an MRI-safe fire extinguisher? Traditional fire extinguishers are made of metal and can be attracted by the MRI magnet, which could pose a significant danger if a fire broke out in the room.

4. Is the furniture and equipment in the room MRI-safe? Metal beds, IV poles and wheelchairs can be very dangerous in the MRI suite. Once an object is attached to the strong magnet, it can be very difficult to remove and it can take several people to pry it off the machine.

5. Where are outside metal objects stored in the facility? Sometimes patients come to be scanned in their own wheelchairs or with their own oxygen tanks or equipment. The MRI magnet can attract any metal in these items. Therefore, the facility should have a dedicated area where potentially problematic equipment and personal items can be safely stored.

6. What happens if a patient develops breathing problems while having a scan? Some facilities are equipped with special oxygen sources that can be used during a scan. However, if a patient requires any type of medical attention, he/she should be removed from the room and taken to a safe area before treatment is given.

7. What steps do you take to prevent someone from bringing unsafe objects into the magnet room? MRI facilities should screen patients for any metal objects. Checklists are often provided to reduce the chance something will be overlooked (like a metal snap on a piece of clothing). Some facilities are using special metal detectors that detect the presence of iron in objects.

8. How do you prevent inadvertent entrance into the room during a scan? People who accidentally wander into the room during a scan may bring along pens, cleaning equipment, or other metallic devices that could be pulled into the scanner. If there is no locked door into the magnet room, the MRI technologist should have a clear view of the door to watch for unauthorized entry.

9. Is everyone who will be in the suite at the time of scan trained in MRI safety? MRI facilities should train all staff in safety measures - including those in housekeeping, transportation and administrative positions.

10. Does the facility share space with other types of imaging devices? If CT scans, X-rays, PET scans or ultrasounds are offered in the same facility, there is a chance a patient receiving a different type of scan may wander into the MRI area. If the person carried anything metal, the object could potentially be grabbed and drawn into the magnet.

Dr. NessAiver has put together some background information on MRI safety on his website at http://www.simplyphysics.com

For the list of 10 questions to ask your MRI facility and providers, visit the following website: http://www.koppdevelopment.com. Follow the MRI safety links, then click on the selection for "10 questions."

For general information about magnetic resonance imaging: American College of Radiology, public website, http://www.radiologyinfo.org Food and Drug Administration, Center for Devices and Radiological Health, http://www.fda.gov/cdrh Institute for Magnetic Resonance Safety, Education, and Research, http://www.imrser.org, or http://www.mrisafety.com Junk Architects, PC, http://www.mri-planning.com