Risk from magnetic fields:

Magnetic resonance imaging (MRI), Functional magnetic resonance imaging (FMRI) Magnetic resonance spectroscopy (MRS)

These scans use strong magnets to develop pictures of the brain. This means that a person must remove all jewelry, piercings, and clothing with metal before entering the scanning machine. Medication patches, such as nicotine patches or ones that release hormones, sometimes contain metal in the sticky backing, which can burn the skin if worn during an MRI. If you use such patches, talk to your doctor about if and when you should remove them. It’s important to tell your doctor if you have any metal in your body, such as metal braces or metal fillings in your teeth, embedded bullets, shrapnel, or implanted medical devices – pacemakers, aneurysm clips, medication pumps, metal plates, screws, or pins. If located close to the head, they may distort the scanned image. Sometimes, the strong magnetic field causes these objects to move, which can cause an injury. If you’re not sure about your risk, check with the doctor before getting this type of brain scan. Magnetoencephalography (MEG) scanning does not carry these risks because it does not use magnets.

Risk from radiation:

Computed tomography (CT) or computed axial tomography (CAT), Positron emission tomography (PET), Single positron emission computed tomography (SPECT)

These scans expose people to low levels of radiation. For example, the amount of radiation from one CT scan of the head is about the same as the amount that the average person receives from natural sources of radiation over eight months.1 1 Computed Tomography (CT) – Head. http://www. radiologyinfo.org/en/info.cfm?pg=headct. Accessed on June 18, 2008. Natural sources of radiation include naturally occurring radioactive materials and cosmic rays such as emitted by the sun. Also, some people may be allergic to the chemicals, called contrast dyes or tracers, used to make sure brain structures show up in these types of scans. In some cases, these chemicals are radioactive but lose their potency fairly quickly. If you have ever had a bad reaction to a contrast dye or tracer, tell the doctor before you get the scan. In general, children should not have PET or SPECT scans.

1 Computed Tomography (CT) – Head. http://www. radiologyinfo.org/en/info.cfm?pg=headct. Accessed on June 18, 2008.

For more detailed descriptions of the different types of brain scans and other tests used to diagnose brain disorders, see the booklet “Neurological Diagnostic Tests and Procedures,” distributed by the National Institute on Neurological Disorders and Stroke (http://www.ninds.nih.gov).