The Facts About MRIs and Metal Implants

Magnetic waves can displace or damage certain devices

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Over two million Americans have an implanted medical device of which 50 percent will need evaluation requiring magnetic resonance imaging (known as an MRI scan). MRIs are used to diagnose and monitor many types of medical conditions, including orthopedic and cardiovascular problems. However, people with certain types of metal implant may not be able to undergo the procedure. 

The reason for this that MRIs use a very strong magnetic field to create diagnostic images. Some metal implants can not only distort the imaging, they can be adversely affected by the powerful magnetic waves.

The radio frequency (RF) energy created by an MRI may cause certain devices to malfunction or significantly heat up, potentially damaging the device and injuring the individual. Vibration and displacement of an implant have also been known to occur.

Implants Potentially Affected by MRIs

The metal implants that are most prone to problems during MRIs include:

Many individuals with these types of implants cannot have an MRI. In addition, persons who have been injured by bullets or shrapnel, or those who work with metals, should be specifically questioned to determine whether an MRI is possible.

Not all metal implants are affected by an MRI. Some have been classified as being "MRI safe" while others are considered "MRI conditional." In fact, some of the newer pacemakers and cochlear implants use advanced technologies and are considered safe when under the influences of an MRI.

Ferromagnetic Versus Non-Ferromagnetic Implants

There are two types of metal that are used, either in part or in whole, in certain implants. One is ferromagnetic and the other is non-ferromagnetic.

Ferromagnetic metals such as iron, nickel, and cobalt are those that, when placed in a magnetic field, become a magnet themselves. When these metals come under the influence of an MRI, problems can occur.

Firstly, the MRI and the ferromagnetic metal become individual magnets with a negative and positive pole. As with all magnets, the two will be attracted and immediately align pole-to-pole. With one magnet (the MRI) weighing several tons and the other (the ferromagnetic implant) weighing several ounces, the more powerful magnetic influence can cause the implant to twist, turn, and even displace entirely. 

Non-ferromagnetic metals are those that don't become magnets under the influence of an MRI. That doesn't mean, however, that they will be problem-free. Non-ferromagnetic metals can still interfere with the magnetic field created by the MRI and distort images so that they can't be read properly.

Additionally, the RF energy created by the MRI can cause problems with any conductive metal within an implant that can inadvertently become a radio transceiver. When this happens, the metal can absorb the RF energy and begin to overheat, potentially damage the implant and any tissue surrounding it.

Metal Implants and MRI Safety

Today, most metal implants, including orthopedic prostheses and dental implants, are made with MRI-safe metals such as titanium. These include hip and knee replacement components (plates, screws, rods) and cavity fillings.

While all of these implants can distort the MRI image if near the body part being scanned, they will usually do not cause problems that an experienced technician can't overcome.

When it comes to MRI safety, the bottom line is this: always advise your doctor and MRI staff of any implant you have that they may otherwise be unaware of. Even if you think the implant is compatible, it is important to let the technicians know in order to for them confirm that it is either MRI safe or MRI conditional. Other imagining options ( CT scans, PET scans) may be available.

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