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Magnetic Resonance Imaging (MRI) (cont.)

Risks

MRI is a very safe procedure. The strong magnetic field itself does not hurt people, unless they have certain types of metal implanted in their body. The magnetic field can cause certain types of metal to move, which could potentially cause an injury.

People with any metal on or in their bodies should tell the technologist. Most people who have metal in their body after surgery can have an MRI. For example, people with hip or knee replacements can have an MRI as soon as 6 weeks after surgery. Other implanted devices require less time after surgery.
Certain devices (eg, heart pacemakers, some implanted pumps, nerve stimulators) can never go into the MRI machine, as they may malfunction or become damaged. Some brain aneurysm clips also cannot go into the scanner.
People who have had prior surgery must inform the technologist prior to the scan. Also, if metal might be in any part of the body from a prior injury or accident, people must inform the technologist prior to the scan. Certain people should not be scanned. For example, in a rare case, one person went blind from being scanned because he had metal in his eye from a welding injury.
Some MRI exams require an injection of an MRI contrast or dye. This MRI contrast or dye is very safe and is completely different from the contrast agent or dye used for imaging tests using x-rays, such as an intravenous pyelogram (IVP) or a CT scan. Allergic reactions to the contrast used are possible but extremely uncommon. The doctor and the MRI technologist should be informed beforehand of any allergies.
An MRI has no known side effects on pregnancy. Most centers will scan pregnant women in their second and third trimesters.