Brain & Nervous System Health Center

What Affects the Test

Reasons you may not be able to have the test or why the results may not be helpful include:

• Pregnancy. An MRI test usually is not done during pregnancy.
• Medical devices that use electronics, such as a pacemaker or medicine infusion pump. The MRI magnet may cause problems with these devices, and that may keep you from having an MRI.
• Medical devices that have metal in them. The metal might make some of the detailed MRI pictures blurry. This may prevent your doctor from seeing the organ that is being looked at. For example, any metal in your spine may prevent your doctor from seeing it clearly.
• Inability to remain still during the test.
• Obesity. A person who is very overweight may not fit into standard MRI machines.

Many modern medical devices that do not use electronics-such as heart valves, stents, or clips-can be safely placed in most MRI machines. But some newer MRI machines have stronger magnets. The safety of MRI scans with these stronger MRI magnets in people with medical devices is not known.

What To Think About

• Sometimes your MRI test results may be different from the results of CT, ultrasound, or X-ray tests, because the MRI scan shows tissue differently.
• Magnetic resonance imaging (MRI) of the spine can often be used instead of other tests that use X-rays, such as a computed tomography (CT) scan or myelography.
• MRI is a safe test for looking at structures and organs inside the body. It costs more than other methods and may not be available in your area.
• Open MRI machines are now made so that the magnet does not completely surround you. But these machines may not be available in all medical centers. Open MRI is useful for people who are claustrophobic or obese.
• Contrast material that contains gadolinium may cause a serious skin problem (called nephrogenic fibrosing dermopathy) in people with kidney failure. Before having an MRI scan, tell your doctor if you have serious kidney disease or if you have had a kidney transplant.