A head MRI (magnetic resonance imaging) is an imaging test that uses powerful magnets and radio waves to create pictures of the brain and surrounding nerve tissues.
It does not use radiation.
Nuclear magnetic resonance - cranial; Magnetic resonance imaging - cranial; MRI of the head; MRI - cranial; NMR - cranial; Cranial MRI; Brain MRI; MRI - brain; MRI - head
How the Test is Performed
Head MRI is done in the hospital or radiology center.
You lie on a narrow table, which slides into a large tunnel-shaped scanner.
Some MRI exams require a special dye, called 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 watches you from another room. The test most often lasts 30 to 60 minutes, but may take longer.
How to Prepare for the Test
You may be asked not to eat or drink anything for 4 to 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.
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.
Before the test, tell your health care provider if you have:
Structural problems in the brain, blood vessels, or pituitary gland
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, tell your 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:
Head CT scan
Positron emission tomography (PET) scan of the brain
A CT scan may be preferred in the following cases, since it is faster and usually available right in the emergency room:
Acute trauma of the head and face
Bleeding in the brain (within the first 24 to 48 hours)
Early symptoms of stroke
Skull bone disorders and disorders involving the bones of the ear
Broder J, Preston R. Imaging of the head and brain. In: Broder J, ed. Diagnostic Imaging for the Emergency Physician. Philadelphia, PA: Elsevier Saunders; 2011:chap 1.
Wilkinson ID, Graves MJ. Magnetic resonance imaging. In: Adam A, Dixon AK, Gillard JH, Schaefer-Prokop CM, eds. Grainger & Allison's Diagnostic Radiology: A Textbook of Medical Imaging. 6th ed. Philadelphia, PA: Elsevier Chuchill Livingstone; 2014:chap 5.
Jason Levy, MD, Northside Radiology Associates, Atlanta, GA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.