What is magnetic resonance imaging (MRI)?
Magnetic resonance imaging (MRI) is a medical imaging technology that uses a magnetic field and computer-generated radio waves to create detailed images of the organs and tissues in your body.
Most MRI machines are large tube-shaped magnets. When you lie inside the MRI machine, the magnetic field temporarily realigns the water molecules in your body. The radio waves cause these aligned atoms to produce faint signals, which are used to create cross-sectional MRI images – like slices in a loaf of bread. The MRI machine can likewise deliver 3D pictures that can be seen from various edges.
How does MRI work?
MRI machines use powerful magnets that produce a strong magnetic field that forces the protons in the body to conform to that field. When the radiofrequency current pulses through the patient, the protons are stimulated, spin out of equilibrium, tensing against the magnetic field pull. When the radiofrequency field is turned off, the MRI sensors are able to detect the energy released during the rearrangement of the protons with the magnetic field. The time it takes for protons to realign the magnetic field, as well as the amount of energy released, varies depending on the environment and the chemical nature of the molecules. Doctors can tell the difference between different types of tissue based on these magnetic properties.
To obtain an MRI image, the patient is placed inside a large magnet and it must remain still during the imaging process so that the image is not blurred. Contrast agents (which often contain gadolinium) may be given to the patient intravenously before or during the MRI to increase the speed of the realignment of protons with the magnetic field. The faster the protons are realigned, the brighter the image.
What are the uses of an MRI?
An MRI scan can be used as a very accurate way to detect disease throughout the body and is often used after other tests have failed to provide enough information to confirm a patient’s diagnosis. In the head, trauma to the brain can be seen as a haemorrhage or swelling. Other abnormalities that are often found include brain aneurysms, stroke, and brain tumors, in addition to tumors or inflammation of the spine.
Neurosurgeons use an MRI scan not only to define the anatomy of the brain but also to evaluate the integrity of the spinal cord after trauma. It is also used when thinking about the problems associated with the vertebrae or intervertebral discs in the spine. An MRI scan can evaluate the structure of the heart and aorta, as it can detect an aneurysm or a tear. MRI scans are not the first line of imaging testing for these problems or in cases of trauma.
It provides valuable information on glands and organs inside the abdomen, and accurate information on the joint structure, soft tissues, and bones of the body. Often times, surgery can be delayed or directed with more precision after the results of the MRI scan are known.
Risks of magnetic resonance imaging
Because an MRI uses strong magnets, the presence of metal in your body can pose a safety risk if you are attracted to the magnet. Even if you are not attracted to the magnet, metallic objects can distort the MRI image. Before having an MRI, you’ll probably finish a survey that incorporates whether you have metal or electronic gadgets in your body.
Unless your device is certified as safe for MRI, you may not be able to get an MRI scan. Hardware included:
- Metallic joint prostheses
- Implanted nerve stimulators
- An implantable heart defibrillator
- A bullet, shrapnel, or any other type of metal fragment
- Cochlear implants
- Intrauterine device
- Implanted drug infusion pumps
- A pacemaker
- Artificial heart valves
- Metal clips
- Metal pins, screws, plates, stents, or surgical staples
If you have permanent tattoos or makeup, ask your doctor if they will affect the MRI. Some darker inks contain a mineral.
Before scheduling an MRI scan, tell your doctor if you think you could be pregnant. The effects of magnetic fields on fetuses are not well understood. Your doctor may recommend an alternative test or delay the MRI. Also tell your doctor if you are breast-feeding a baby, especially if you will be receiving a contrast material during the procedure.
It is also important to discuss kidney or liver problems with your doctor and technologist, as problems in these organs may limit the use of the contrast agents injected during the examination.
How should I prepare for an MRI?
When you make your MRI appointment, you’ll get detailed instructions on how to prepare.
- What are you going to eat: You may need to avoid eating for two hours or more before the MRI.
- Topics for discussion: Tell your doctor about any medications you are taking. Also mention if you have any allergies to any medication or any other medical condition. Women should tell their doctors if there is any possibility of pregnancy.
- It is important to mention any metal implants or metal fragments in your body. They can cause serious, even fatal, problems when exposed to the magnetic traction of an MRI. For example, people who use pacemakers cannot have an MRI.
- Consider asking if you can bring music to the appointment. Some centres allow people to listen to music through headphones during an MRI scan. It may help to distract you from the loud noises made by the MRI machine.
- Insurance, costs, and approval: Before your appointment, ask your health insurance provider what costs will be covered. Discover the amount you should pay. Once you get to the doctor’s office or hospital, you will be asked to sign a consent form. This form demonstrates that you understand the benefits and risks of the procedure and that you agree to it.
During the magnetic resonance imaging test
What should I wear?
Before the test, you will remove the jewellery and other metal items. You may also need to wear a hospital gown.
What will happen during the operation?
- Depending on the part of your body to be scanned, you may be given a contrast medium. This is a special dye. It is given intravenously (IV) or orally.
- If the dye is given through a vein, the nurse or doctor will insert a small needle into a vein in your arm or hand. The saline solution will flow through the line until the dye is injected. Brine is a mixture of salt and water. Once infused, the colour will go through the circulation system and help make a more clear image of explicit pieces of your body.
- Next, you’ll lie on a moveable examination table outside of the MRI machine. You will lie on your back with your arms at your side, with your head on a headrest.
- Small devices, called coils, help transmit and receive radio waves. These may be placed over or around a part of your body to create a clearer image.
- When you are ready, the examination table will slide through the hole in the centre of the MRI machine. You will need to lie down while the device takes a series of photos. Each series will last up to 15 minutes. You may need to get 2 to 6 sets. This means the Magnetic resonance imaging usually lasts for up to 90 minutes. The technician can give you an estimate of time before you begin.
- During the examination, the technologist will be in an adjacent computer room, separated by a window. The technologist will be able to see you. You will be able to speak with the technician through the intercom system.
- You will know when the device is taking pictures because you will hear loud banging sounds. Also, the part of your body being examined may feel warm during the MRI. This is normal.
- Magnetic resonance imaging is not painful. But you may feel uncomfortable when lying. If you received an IV, you may feel discomfort when the needle is inserted. Intravenous saline may feel cold at the injection site.
- Meanwhile, some people find the loud device sounds annoying. You can reduce this discomfort by wearing earplugs or listening to music.
- If you are afraid of small spaces, tell the technician before starting the examination. A radiologist may be able to give you medication to help you relax. This drug is called a sedative.
- Once the MRI is complete, you may be asked to remain on the examination table while a radiologist reviews the images to see if more is needed.
After a magnetic resonance imaging scan
After the examination, the radiologist will examine the images to check if more is needed. In the event that the radiologist is fulfilled, the patient can return home.
The radiologist prepares a report for the requesting physician. Patients are generally approached to make a meeting with their primary care physician to examine the outcomes.
Results of magnetic resonance imaging
A doctor specially trained to interpret an MRI (radiologist) will analyze the images taken from the scan and report the results to your doctor. Your doctor will discuss the important results and the next steps with you.