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A head MRI (magnetic resonance imaging) scan of the head is a imaging test that uses powerful magnets and radio waves to create pictures of the brain and surrounding nerve tissues.
It does not use radiation.
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You may be asked to wear a hospital gown or clothing without metal fasteners (such as sweatpants and a t-shirt). Certain types of metal can cause blurry images.
You will lie on a narrow table, which slides into a large tunnel-shaped scanner.
Some exams require a special dye (contrast). The dye is usually given before the test through a vein (IV) in your hand or forearm. The dye helps the radiologist see certain areas more clearly.
During the MRI, the person who operates the machine will watch you from another room. The test most often lasts 30 - 60 minutes, but it may take longer.
You may be asked not to eat or drink anything for 4 - 6 hours before the scan.
Tell your doctor if you are afraid of close spaces (have claustrophobia). You may receive medicine to help you feel sleepy and less anxious, or your doctor may suggest an "open" MRI, in which the machine is not as close to the body.
Before the test, tell your health care provider if you have:
The MRI contains strong magnets. Metal objects are not allowed into the room with the MRI scanner. This includes:
An MRI exam causes no pain. If you have difficulty lying still or are very nervous, you may be given a medicine to relax you. Too much movement can blur MRI images and cause errors.
The table may be hard or cold, but you can request a blanket or pillow. The machine produces loud thumping and humming noises when turned on. You can wear ear plugs to help reduce the noise.
An intercom in the room allows you to speak to someone at any time. Some MRIs have televisions and special headphones that you can help you pass the time or block the scanner noise.
There is no recovery time, unless you were given a medicine to relax. After an MRI scan, you can go back to your normal diet, activity, and medications.
MRI provides detailed pictures of the brain and nerve tissues.
A brain MRI can be used to diagnose and monitor many diseases and disorders that affect the brain, including:
An MRI scan of the head can also determine the cause of:
A special type of MRI called magnetic resonance angiography (MRA) may be done to look at blood vessels in the brain.
Abnormal results may be due to:
MRI uses no radiation. To date, no side effects from the magnetic fields and radio waves have been reported.
The most common type of contrast (dye) used is gadolinium. It is very safe. Allergic reactions to the substance rarely occur. However, gadolinium can be harmful to patients with kidney problems who require dialysis. If you have kidney problems, please tell your health care provider before the test.
The strong magnetic fields created during an MRI can make heart pacemakers and other implants not work as well. It can also cause a piece of metal inside your body to move or shift.
Tests that may be done instead of an MRI of the head include:
A CT scan may be preferred in the following cases, since it is faster and usually available right in the emergency room:
Wilkinson ID, Paley MNJ. Magnetic resonance imaging: basic principles. In: Grainger RC, Allison D, Adam, Dixon AK, eds. Diagnostic Radiology: A Textbook of Medical Imaging. 5th ed. New York, NY: Churchill Livingstone; 2008:chap 5.
Saunders D, Jäger HR, Murray AD, Stevens JM. Skull and brain: methods of examination and anatomy. In: Grainger RC, Allison D, Adam, Dixon AK, eds. Diagnostic Radiology: A Textbook of Medical Imaging. 5th ed. New York, NY: Churchill Livingstone; 2008:chap 55.