How to Prepare for a MRI of the Head
You may be asked to wear a gown during the exam or you may be allowed to wear your own clothing if it is loose-fitting and has no metal fasteners.
Guidelines about eating and drinking before an MRI exam vary with the specific exam. For some types of exams, you will be asked to fast for 8-12 hours. Unless you are told otherwise, you may follow your regular daily routine and take medications as usual.
Some MRI exams require you to swallow contrast material or receive an injection of contrast into the bloodstream. The radiologist or technologist may ask if you have allergies of any kind, such as allergy to iodine or X-ray contrast material, drugs, food, the environment, or asthma. The contrast material used for an MRI exam, called gadolinium, does not contain iodine and is less likely to cause side effects or an allergic reaction.
The radiologist should also know if you have any serious health problems or if you have recently had surgery. Some conditions, such as severe kidney disease may prevent you from being given contrast material for an MRI. If there is a history of kidney disease, it may be necessary to perform a blood test to determine whether the kidneys are functioning adequately.
Women should always inform their doctor or technologist if there is any possibility that they are pregnant. MRI has been used for scanning patients since the 1980s with no reports of any ill effects on pregnant women or their babies. However, because the baby will be in a strong magnetic field, pregnant women should not have this exam unless the potential benefit from the MRI is assumed to outweigh the potential risks.
If you have claustrophobia (fear of enclosed spaces) or anxiety, you may want to ask your doctor for a prescription for a mild sedative prior to the scheduled examination.
Jewelry and other accessories should be left at home or removed prior to the MRI scan. Because they can interfere with the magnetic field of the MRI unit, metal and electronic objects are not allowed in the exam room. These items include:
- Jewelry, watches, credit cards and hearing aids, all of which can be damaged.
- Pins, hairpins, metal zippers and similar metallic items, which can distort MRI images.
- Removable dental work.
- Pens, pocketknives and eyeglasses.
- Body piercings.
In most cases, an MRI exam is safe for patients with metal implants, except for a few types. People with the following implants cannot be scanned and should not enter the MRI scanning area unless explicitly instructed to do so by a radiologist or technologist who is aware of the presence of any of the following:
- Internal (implanted) defibrillator or pacemaker
- Cochlear (ear) implant
- Some types of clips used on brain aneurysms
You should tell the technologist if you have medical or electronic devices in your body, because they may interfere with the exam or potentially pose a risk, depending on their nature and the strength of the MRI magnet. Examples include but are not limited to:
- Artificial heart valves
- Implanted drug infusion ports
- Implanted electronic device, including a cardiac pacemaker
- Artificial limbs or metallic joint prostheses
- Implanted nerve stimulators
- Metal pins, screws, plates, stents or surgical staples
In general, metal objects used in orthopedic surgery pose no risk during MRI. However, a recently placed artificial joint may require the use of another imaging procedure. If there is any question of their presence, an X-ray may be taken to detect the presence of and identify any metal objects.
Patients who might have metal objects in their bodies also may require an X-ray prior to an MRI. You should notify the technologist or radiologist of any shrapnel, bullets, or other pieces of metal which may be present in your body due to accidents. Dyes used in tattoos may contain iron and could heat up during MRI, but this is rarely a problem. Tooth fillings and braces usually are not affected by the magnetic field but they may distort images of the facial area or brain, so the radiologist should be aware of them.