The Knowledge Zone
How should I prepare for the procedure?
You will usually be asked to change into a gown before the exam to avoid any metal objects that may be in your clothing. Some modern materials used in clothing contain trace metals that may impact the scanning process.
EATING AND DRINKING
Guidelines about eating and drinking before an MRI exam vary with the specific exam. Unless you are told otherwise, you may follow your regular daily routine and take food and medications as usual but in some instances we may ask you to fast for a few hours before the scan.
INJECTIONS AND ALLERGIES
Some MRI examinations may require you to receive a contrast agent via an intravenous injection. The technologist may ask if you have any allergies to any drugs, food or the environment or if you have asthma. If you do then you should let them know. The contrast agent used in MRI contains a metal called gadolinium and is different from the iodine based agent used for X-ray and CT. So you can use the MRI agent even if you are allergic to iodine in shellfish. It is far less common for a patient to have an allergy to a gadolinium-based contrast compared to iodine. If you do have a history of allergies then your doctor or our radiologist may recommend that you get certain pre-medications before the injection. Your written consent will be required before giving you the contrast agent because of the small risk of serious allergic reactions. Please consult the ACR Website for more information on Contrast Media.
HEALTH ISSUES AND SURGERIES
You should also let the radiologist know if you have any serious health problems, or if you have had any recent surgeries. Some conditions, such as severe kidney disease, may prevent you from being given gadolinium contrast for an MRI. If you have a history of kidney disease or liver transplant, it will be necessary to perform a blood test to determine whether the kidneys are functioning adequately.
Women should always inform their physician 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 unborn babies. However, because the unborn baby will be in a strong magnetic field, pregnant women should not have this exam in the first three to four months of pregnancy unless the potential benefit from the MRI exam is deemed by your doctor to outweigh any potential risks. Pregnant women should not receive injections of gadolinium contrast material except when absolutely necessary for medical treatment.
If you have claustrophobia (fear of enclosed spaces) or anxiety, you may want to ask your physician for a prescription for a mild sedative prior to your scheduled examination.
JEWELLERY AND ACCESSORIES
Jewellery and other accessories should be left at home, if possible, or removed prior to the MRI scan. Because they can interfere with the magnetic field of the MRI unit, metal and electronic items are not allowed in the exam room. In addition to affecting the MRI images, these objects can become projectiles within the MRI scanner room and may cause you and/or others nearby harm. 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, pocket knives and eyeglasses
IMPLANTS AND MEDICAL DEVICES
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:
cochlear (ear) implant
some types of clips used for brain aneurysms
some types of metal coils placed within blood vessels
most cardiac defibrillators and pacemakers unless they are a recent model that is specifically designated MRI safe under certain conditions in which case special arrangements must be made.
You should tell the Trained MRI Technologists if you have medical or electronic devices in your body. These objects may interfere with the exam or potentially pose a risk, depending on their nature and the strength of the MRI magnet. Many implanted devices will have a pamphlet explaining the MRI risks for that particular device. If you have the pamphlet, it is useful to bring that to the attention of the scheduler before the exam and bring it to your exam in case the radiologist or technologist has any questions. Some implanted devices require a short period of time after placement (usually six weeks) before being safe for MRI examinations. Examples include but are not limited to:
artificial heart valves
implanted drug infusion ports
artificial limbs or metallic joint prostheses
implanted nerve stimulators
metal pins, screws, plates, stents or surgical staples
If there is any question of their presence, an x-ray may be taken to detect and identify any metal objects. 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.
Patients who might have metal objects in certain parts of their bodies may also require an x-ray prior to an MRI. You should notify the technologist or radiologist of any shrapnel, bullets, or other pieces of metal that may be present in your body due to prior accidents or if you are at risk of metal fragments in your eyes for example if you do metal work, welding and grinding. Foreign bodies near and especially lodged in the eyes are particularly important because they may move during the scan, possibly causing permanent damage to the eye. Dyes used in tattoos may contain iron and could heat up during an MRI scan, but this is rare. Tooth fillings and braces usually are not affected by the magnetic field, but they may distort images of the facial area or brain, so you should let the radiologist know about them.
INFANTS AND YOUNG CHILDREN
Infants and young children usually require sedation to complete an MRI exam without moving. Whether a child requires sedation depends on the child’s age, intellectual development and the type of exam. Moderate and conscious sedation can be provided at many facilities. A physician specializing in sedation would have to be scheduled to be available during the exam for your child’s safety. You will be given special instructions for how to prepare your child for the sedation.