Before you receive an MRI, a technician will ask you to remove any metal items you are wearing, such as jewellery, glasses or belt buckles. You should tell her about any medical implants you have. The MRI machine's powerful magnetic field attracts ferrous, or iron-containing, metals and can cause serious injury. Even in the absence of injury, metal objects can distort the MRI image and make it difficult to read. Safety experts have cleared some metals for use during MRIs.
Orthopaedic surgeons favour titanium implants for their strength and compatibility with body tissues. Titanium's nonmagnetic properties make it compatible for use with an MRI as well. Joint replacements, surgical screws, bone plates and pacemaker cases all use titanium. In addition, doctors can use surgical tools made of the metal in MRI rooms.
Though cobalt has magnetic properties, implants such as coronary stents made of cobalt-chromium alloy have tested safe during an MRI. The alloy also tests safe for larger items, such as knee and hip replacements.
Researchers have tested intrauterine contraceptive devices (IUDs) for MRI safety. Some of these devices have a small copper coil. The magnetic field didn't move the IUD at field strengths up to 3 teslas, nor did the copper heat up. Some metal objects become warm during an MRI, even if the magnetic field doesn't pull at them. Copper wiring for pacemakers has also tested safe for an MRI.
Some stainless steel alloys have a very low reaction, or susceptibility, to magnetic fields. Medical supply companies sell stainless steel tools and accessories that staff can safely use in the MRI room. Stainless steel items such as dental braces can distort MRI images, however. If the metal interferes too much with the MRI image, the doctor may recommend you have your braces removed.
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