An MRI scan — short for magnetic resonance imaging — is one of the most powerful and safe tools doctors use to see inside your body. Unlike X-rays or CT scans, an MRI scan uses no radiation at all. Instead, it uses a strong magnetic field and radio waves to create detailed images of your organs, tissues, and bones. In this article, we explain how MRI scans work, what to expect during the procedure, who should avoid them, and how to access one through Canada’s healthcare system.
What Is an MRI Scan?
An MRI scan is a non-invasive medical imaging technique. It produces highly detailed pictures of the inside of the human body without using X-ray radiation. This makes it a preferred choice for imaging soft tissues, the brain, the spine, joints, and internal organs.
The full name is magnetic resonance imaging (MRI). In French, you may see it written as IRM (imagerie par résonance magnétique), which you might encounter on Quebec health forms. Both refer to the same procedure.
According to Health Canada, medical imaging technologies like MRI are a core part of diagnostic medicine in Canada. They help doctors detect conditions early and plan the right treatment.
How Does an MRI Scan Work?
Your body is made up of over 90% water. Water contains hydrogen atoms, and those hydrogen atoms have tiny particles called protons. An MRI scan works by using those protons to build an image.
When you enter the MRI machine, a powerful magnet aligns all the hydrogen protons in your body in the same direction. Then, the machine sends radio waves — called radiofrequency (RF) waves — through your body. These waves cause the protons to shift out of alignment. When the radio waves stop, the protons snap back into place and release a small burst of energy. The machine detects that energy and uses it to create a detailed image.
Different tissues in your body contain different amounts of water. As a result, they release different energy signals. Fat and fluid-rich tissues appear bright white on the scan. Dense structures like bone cortex contain very few hydrogen protons, so they appear dark. This contrast helps doctors identify abnormalities with great precision.
What Is Resonance in an MRI?
The word “resonance” refers to the exchange of energy between two systems vibrating at the same frequency. In an MRI scan, the radiofrequency waves are tuned to match the natural vibration frequency of hydrogen protons. This is what makes the technique so precise and selective.
The radio waves used in an MRI fall between 1 and 100 MHz (megahertz). This is similar to the frequency range used by FM radio stations — and just as harmless to human tissue.
Inside the MRI Machine: The Magnet
The heart of every MRI scan machine is a superconducting magnet. This magnet is always on — even when no one is being scanned. It is cooled using liquid helium to maintain its superconducting properties.
Most clinical MRI machines operate at a magnetic field strength of 1.5 tesla (T). This level offers an excellent balance between image quality and safety. Some hospitals and research centres use 3 tesla machines, which produce even sharper images. Research MRI systems used in laboratories can reach 11 to 13 tesla, but these are not used on people.
Why Magnet Strength Matters
Higher magnet strength generally means better image resolution. At 1.5 tesla, an MRI can detect details smaller than 1 millimetre. However, stronger magnets also make the machine more sensitive to interference, which can affect image quality.
Furthermore, 1.5 T remains the standard in most Canadian hospitals because it delivers excellent diagnostic images with minimal distortion. Some specialized centres, such as academic hospitals in Toronto, Montreal, and Vancouver, offer 3 T scanning for complex neurological or musculoskeletal cases.
The Danger of Metal Near an MRI Machine
The MRI magnet is extraordinarily powerful. It can attract a solid iron key from more than 7 metres away. This is not a dramatic exaggeration — it is a real safety concern that MRI technologists take very seriously.
Any metal object near an MRI machine can become a dangerous projectile. This includes everyday medical items like stethoscopes, oxygen tanks, and stretchers. For this reason, strict safety screening is carried out before every scan. You will always be asked to remove all metal objects and complete a safety checklist before entering the scanning room.
Types of Images an MRI Scan Can Produce
One of the biggest advantages of an MRI scan is its flexibility in imaging. It can capture images in multiple planes and orientations.
These include:
Axial plane — horizontal cross-sections, like slices of bread
Sagittal plane — side-to-side views, dividing the body into left and right
Coronal plane — front-to-back views, dividing the body into front and back
Oblique planes — angled views for specific structures
3D images — full three-dimensional reconstructions of organs or regions
This multi-planar capability makes MRI particularly valuable for imaging the brain, spinal cord, knee joints, and pelvic organs. No other common imaging tool offers this level of detail across so many angles without repositioning the patient.
Hypersignal and Hyposignal: Reading the Images
On an MRI image, brightness indicates how strongly a tissue responded to the magnetic pulses. A bright white area is called a hypersignal. A very dark area is called a hyposignal.
For example, cerebrospinal fluid (the fluid around the brain and spinal cord) typically appears bright white. Bone cortex, which has very few hydrogen protons, appears very dark. Radiologists — the doctors who read these images — are trained to interpret these differences and identify anything unusual.
MRI Scan Safety: Who Should Be Careful?
An MRI scan is considered very safe for most people. It does not use ionizing radiation, so it does not carry the same risks as X-rays or CT scans. However, the powerful magnet means certain people need to take extra precautions.
You should always tell your doctor or the MRI technologist if you have any of the following:
A cardiac pacemaker or implantable defibrillator
Cochlear (inner ear) implants
Metal clips from previous brain or vascular surgery
Metal fragments in your eyes or body (from welding or industrial work)
Certain types of joint replacements or surgical hardware
Insulin pumps or nerve stimulators
Tattoos with metallic-based pigments (a rare concern)
Many modern implants are MRI-compatible, but it depends on the specific device. Always disclose your full medical history before the scan. The MRI team will verify whether it is safe to proceed.
Is MRI Safe During Pregnancy?
MRI scans are generally avoided during the first trimester of pregnancy unless medically necessary. After that, they are considered safe and are sometimes used when ultrasound does not provide enough information. Your doctor will weigh the benefits and risks for your specific situation. Always inform the MRI team if there is any chance you could be pregnant.
What About Claustrophobia?
Some people feel anxious or claustrophobic inside the narrow MRI tube. This is very common and nothing to be embarrassed about. If you are concerned, talk to your family doctor beforehand. In some cases, a mild sedative can be prescribed to help you relax. Open MRI machines are also available at some centres, though they typically have lower magnet strength.
Getting an MRI Scan in Canada
In Canada, MRI scans are covered by provincial and territorial health plans when they are medically necessary. However, you generally need a referral from a physician. You cannot simply walk into an imaging centre and book an MRI on your own — at least not through the public system.
Your family doctor or specialist will order the scan if they believe it is clinically indicated. The referral is sent to a hospital radiology department or an outpatient imaging centre. Wait times vary significantly by province. In some areas, non-urgent MRI scans can take weeks or months.
Private MRI Options in Canada
Private MRI clinics exist in several provinces, including British Columbia, Alberta, and Ontario. These clinics allow patients to pay out of pocket for faster access. Costs typically range from $600 to over $1,500 depending on the body part being scanned and the facility.
However, even with a private scan, a radiologist must interpret the results and forward a report to your referring physician. The images alone are not a diagnosis. Always work with your doctor to understand what the results mean for your health.
For more information on diagnostic imaging in Canada, visit Mayo Clinic’s guide to MRI procedures for a helpful overview of what to expect.
What to Expect During Your MRI Scan
Knowing what to expect can ease a lot of anxiety. Here is a simple walkthrough of a typical MRI scan appointment.
Before the scan, you will complete a metal safety screening form. You will be asked to remove jewellery, piercings, hearing aids, glasses, and any removable dental work. You will change into a hospital gown. A technologist will explain the procedure and answer your questions.
During the scan, you will lie on a padded table that slides into the MRI machine. The machine makes loud knocking and banging sounds during the scan — this is completely normal. You will be given earplugs or headphones to reduce the noise. Some centres play music through the headphones to help you relax. It is important to stay very still so the images are clear.
After the scan, you can return to your normal activities immediately. There is no recovery time required. A radiologist will review your images and send a report to your referring doctor, who will discuss the results with you at a follow-up appointment.
How Long Does an MRI Take?
Most MRI scans take between 30 and 60 minutes. Complex scans of the brain or spine may take longer. Some scans require an injection of contrast dye to highlight certain structures. If this is needed, the technologist will place a small IV in your arm before the scan begins. Healthline’s overview of MRI scanning offers additional detail on contrast-enhanced imaging.
When to See a Doctor
You do not book an MRI scan yourself — your doctor does that for you. However, there are situations where you should speak with your family doctor or visit a walk-in clinic and ask whether an MRI might be appropriate for your condition.
Consider speaking with a healthcare provider if you are experiencing:
Persistent or unexplained back or neck pain
Neurological symptoms such as numbness, tingling, or weakness
Unexplained headaches or vision changes
Joint pain that does not improve with conservative treatment
Follow-up imaging after a cancer diagnosis
Symptoms your doctor wants to investigate further after other tests
Your family doctor is your best first point of contact. If you do not have a family doctor, a walk-in clinic can assess your symptoms and refer you if needed. Many provinces also have nurse practitioner-led clinics that can order imaging referrals. Always consult a qualified healthcare professional before drawing conclusions about your health.
Frequently Asked Questions About MRI Scans
Is an MRI scan safe?
Yes, an MRI scan is considered very safe for most people. It does not use radiation, making it safer than X-rays or CT scans in that regard. However, the strong magnet means people with certain metal implants or devices may not be able to have one — always tell your doctor about any implants before your scan.
Does an MRI scan hurt?
No, an MRI scan is completely painless. You will not feel the magnetic field or the radio waves. The main discomfort most people notice is the loud noise the machine makes and, for some, the feeling of being in a narrow space. If you are anxious about the procedure, talk to your doctor beforehand about your options.
How long does an MRI scan take?
Most MRI scans take between 30 and 60 minutes, depending on the body part being imaged. Brain and spinal MRIs can sometimes take a little longer. Your technologist will give you a time estimate before the scan begins so you know what to expect.
Is an MRI scan covered by provincial health insurance in Canada?
Yes, MRI scans are covered by provincial health plans across Canada when they are medically necessary and ordered by a physician. You will need a referral from your family doctor or a specialist. Wait times vary by province, and some people choose to pay for a private scan for faster access.
Can I have an MRI scan if I have metal in my body?
It depends on the type of metal. Many modern surgical implants and joint replacements are MRI-compatible, but some older devices or certain pacemakers are not. Always disclose your complete medical history to the MRI team before your scan so they can verify whether it is safe for you to proceed.
What is the difference between an MRI scan and a CT scan?
Both are medical imaging tools, but they work very differently. A CT (computed tomography) scan uses X-ray radiation to create images, while an MRI scan uses a magnetic field and radio waves — no radiation at all. MRI is generally better for soft tissue detail, such
