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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.
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
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.
How to Prepare for the Test
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:
- Brain aneurysm clips
- Certain types of artificial heart valves
- Heart defibrillator or pacemaker
- Inner ear (cochlear) implants
- Kidney disease or dialysis (you may not be able to receive contrast)
- Recently placed artificial joints
- Certain types of vascular stents
- Worked with sheet metal in the past (you may need tests to check for metal pieces in your eyes)
Because the MRI contains strong magnets, metal objects are not allowed into the room with the MRI scanner:
- Pens, pocketknives, and eyeglasses may fly across the room.
- Items such as jewelry, watches, credit cards, and hearing aids can be damaged.
- Pins, hairpins, metal zippers, and similar metallic items can distort the images.
- Removable dental work should be taken out just before the scan.
How the Test Will Feel
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 use to help the time pass.
There is no recovery time, unless you were given a medicine to relax. After an MRI scan, you can resume your normal diet, activity, and medications.
Why the Test is Performed
MRI provides detailed pictures of the brain and nerve tissues. It also provides clear pictures of parts of the brain that are difficult to see clearly on CT scans.
A brain MRI can be used to diagnose and monitor many diseases and disorders that affect the brain, including:
- Birth defect of the brain
- Bleeding in the brain (subarachnoid or intracranial hemorrhage)
- Brain infection
- Brain tumors
- Hormonal disorders (such as acromegaly, galactorrhea, and Cushing syndrome)
- Multiple sclerosis
An MRI scan of the head can also determine the cause of:
- Muscle weakness or numbness and tingling
- Changes in thinking or behavior
- Hearing loss
- Headaches when certain other symptoms or signs are present
- Speaking difficulties
- Vision problems
A special type of MRI (called MRA, or magnetic resonance angiography) may be done to look at blood vessels in the brain. For more information see: MRA
What Abnormal Results Mean
Abnormal results may be due to:
- Abnormal blood vessels in the brain (arteriovenous malformations of the head)
- Acoustic neuroma
- Bleeding in the brain
- Brain abscess
- Brain aneurysms
- Brain tissue swelling
- Brain tumors
- Damage to the brain from an injury
- Hydrocephalus (fluid collecting around the brain)
- Infection of the bones (osteomyelitis)
- Loss of brain tissue
- Multiple sclerosis
- Optic glioma
- Pituitary tumor
- Stroke or transient ischemic attack (TIA)
- 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, 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:
- Cranial CT scan
- Positron emission tomography (PET) scan of the brain
- Skull x-ray
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 - 48 hours)
- Early symptoms of stroke
- Skull bone disorders and disorders involving the bones of the ear
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.
Reviewed By: Ken Levin, MD, private practice specializing in Radiology and Nuclear Medicine, Allentown, PA. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M. Health Solutions, Ebix, Inc.