Magnetic resonance imaging (MRI) is a technique that uses a magnetic field and radio waves to create detailed images of the organs and tissues within your body.
Most MRI machines are large, tube-shaped magnets. When you lie inside an MRI machine, the magnetic field temporarily realigns hydrogen atoms in your body. Radio waves cause these aligned atoms to produce very faint signals, which are used to create cross-sectional MRI images — like slices in a loaf of bread.
The MRI machine can also be used to produce 3-D images that may be viewed from many different angles.
An open MRI machine has a larger opening and doesn’t completely surround the patient as compared to a standard MRI machine. But this kind of open MRI cannot do some types of MRI scans. People who get nervous in small places (are claustrophobic) may feel better using an open MRI machine. An open MRI machine also may be easier to use for people who are very overweight or obese. But not all medical centres have this kind of MRI machine.
Why it’s done
MRI is a noninvasive way for your doctor to examine your organs, tissues and skeletal system. It produces high-resolution images of the inside of the body that help diagnose a variety of problems.
MRI of the brain and spinal cord
MRI is the most frequently used imaging test of the brain and spinal cord. It’s often performed to help diagnose:
- Aneurysms of cerebral vessels
- Disorders of the eye and inner ear
- Multiple sclerosis
- Spinal cord injuries
- Brain injury from trauma
A special type of MRI is the functional MRI of the brain (fMRI). It measures the metabolic changes that occur within the brain. It may be used to examine the brain’s anatomy and determine which parts of the brain are handling critical functions. This helps identify important language and movement control areas in the brains of people being considered for brain surgery. Functional MRI may also be used to assess damage from a head injury or from disorders such as Alzheimer’s disease.
MRI of the heart and blood vessels
MRI that focuses on the heart or blood vessels can assess:
- The size and function of the heart’s chambers
- Thickness and movement of the walls of the heart
- The extent of damage caused by heart attack or heart disease
- Structural problems in the aorta, such as aneurysms or dissections
- Inflammation or blockages in the blood vessels
MRI of other internal organs
MRI may be used to check for tumors or other abnormalities of many organs in the body, including the:
- Liver and bile ducts
MRI of bones and joints
MRI may be used to help evaluate:
- Joint abnormalities caused by traumatic or repetitive injuries, such as torn cartilage or ligaments
- Disk abnormalities in the spine
- Bone infections
- Tumors of the bones and soft tissues
MRI of the breasts
MRI may be used in addition to mammography to detect breast cancer, particularly in women who have dense breast tissue or who may be at high risk of the disease.
Because MRI uses powerful magnets, the presence of metal in your body may be a safety hazard or affect a portion of the MRI image. Before having an MRI, tell the technologist if you have any metal or electronic devices in your body, such as:
- Metallic implant and joint prostheses
- Artificial heart valves
- An implantable heart defibrillator
- A pacemaker
- Metal clips
- Cochlear implants
- A bullet, shrapnel or any other type of metal fragment
- History as metallic worker
If you have tattoos, ask your doctor whether they might affect your MRI. Some of the darker inks may contain metal.
Before you schedule an MRI, tell your doctor if you think you’re pregnant. The effects of magnetic fields on fetuses aren’t well-understood. Your doctor may recommend choosing an alternative exam or postponing the MRI.
It’s also important to discuss any kidney or liver problems with your doctor and the technologist, because problems with these organs may limit the use of injected contrast agents during your scan.
How you prepare
Before an MRI exam, eat normally and continue to take your usual medications, unless otherwise instructed. You will typically be asked to change into a gown and to remove things that might affect the magnetic imaging:
- Hearing aids
- Underwire bras
What can I expect before my MRI exam?
There is little preparation for an MRI exam. Take your daily medications as you normally would, unless instructed otherwise. There are few dietary restrictions for an MRI. For those exams, you will be notified of the requirements.
- Please arrive at least 30 minutes prior to your exam and check in with the receptionist. You will need to complete the MRI screening form.
- To eliminate possible MR safety issues, you will be asked to change into a hospital gown. A locker/safe place will be supplied to secure your belongings.
- A technologist will verify your identification and the requested exam. Your screening form will be reviewed by the technologist in consultation with the radiologist if indicated. If MRI contrast is indicated for the exam, an IV catheter will be inserted in your arm by a nurse or technologist.
What can I expect during my MRI scan?
- The duration of the procedure will vary but the average is 45 minutes to one hour per body part.
- You will be required to lie still during the actual MR scanning. Depending on the body part that is being examined, you may be instructed to hold your breath for up to 30 seconds.
- The magnet is permanently open on both ends. It is well lit and there is a fan for patient comfort. There is also a two way intercom system for communication between patient and technologist. The part of the body being scanned will be placed in the middle of the magnet.
- During the actual imaging, you will hear a loud intermittent banging noise. You will be provided with earplugs or head phones to minimize the noise during the procedure.
- The technologist will also provide you with an alarm button to alert the technologist of any discomfort you may experience at any point during the MRI exam.
- Some MRI exams require an injection of intravenous MRI contrast. Inform the technologist if you experience any discomfort during the injection.
What can I expect after my MRI scan?
- If a dye injection is used, the IV line is removed from the arm before you go home.
- Allergic reaction from gadolinium dye is extremely rare. However, if you experience symptoms such as rash, hives, or shortness of breath, you should notify the technologist immediately if you are still at the imaging facility, or call your doctor or go to the nearest hospital if you have already left the imaging facility.
- In the event that sedation is needed (such as for claustrophobia), you will be sent home once awake and alert. If you receive sedation, someone must drive you home.
A doctor specially trained to interpret MRIs (radiologist) will analyze the images from your scan and report the findings to your doctor. Your doctor will discuss any important findings and next steps with you.