MRI scans explained: how they work and what to expect

Of all the scans, MRI is the one that most often makes people nervous — the big machine, the tunnel, the noise. But it’s also one of the most powerful and safest tools in medicine. Here’s what it actually is, in plain English.

What an MRI is (and why it’s different)

MRI stands for magnetic resonance imaging. Instead of X-rays, it uses a powerful magnet, radio waves and a computer to create images.^[1] The magnet lines up the water molecules in your body; a pulse of radio energy nudges them; and as they settle back, they give off tiny signals that the scanner reads and turns into cross-sectional “slices” a radiologist can view from any angle.^[1]

The crucial point: there’s no ionising radiation.^[3] That’s the big difference from X-ray and CT, and it’s why MRI is often chosen for younger patients, in pregnancy, and any time detailed soft-tissue pictures are needed without a radiation dose.

What MRI is used for

MRI is the preferred scan for soft tissue — the parts an X-ray struggles to show.^[1] It’s used across the body, most commonly for the:

• Brain and spinal cord — stroke, multiple sclerosis, tumours, nerve problems
• Spine — discs, nerve compression, and the cause of persistent back or leg pain
• Joints — knees, shoulders, hips: cartilage, ligaments and tendons
• Muscles and soft tissues
• Abdomen and pelvis, blood vessels, the heart and the breasts^[1]

Because it distinguishes healthy from abnormal tissue so well, MRI often answers questions that other scans can’t.^[1]

What a scan is actually like

In an Australian radiology practice, a radiographer (the health professional who runs the scanner) looks after you. After a safety check (see below), you lie on a padded table that slides into the scanner — a large tube, open at both ends.^[1]

A few things to expect:

• It’s noisy. The machine makes loud tapping and knocking sounds as it works. You’ll get earplugs or headphones, and often music.^[1]
• You must stay still. Movement blurs the images, so you’ll be asked to keep still through each sequence.^[1]
• It’s painless, and you can talk to the radiographer through an intercom, with a call button in your hand the whole time.^[1]
• Time: most scans take 15–45 minutes, occasionally up to an hour, depending on the body part.^[1]

Contrast dye

Some MRIs use a contrast agent (gadolinium) injected into a vein to make certain tissues stand out.^[1] Unlike CT dye, gadolinium contains no iodine and rarely causes allergic reactions.^[1] Tell your team beforehand about kidney problems, a previous reaction, or if you’re breastfeeding — but many MRIs need no contrast at all.

The one big safety step: metal

Because the magnet is always on and extremely strong, the main safety task is making sure no problematic metal goes near it.^[1] Before your scan you’ll fill in a screening form and be asked to remove all metal (jewellery, watches, hairclips, cards, phones) and to declare any implant or device — pacemakers, aneurysm clips, cochlear implants, metal fragments and so on.^[1][5] Many modern implants are “MRI-conditional” (safe to scan under known conditions), which is why the exact details matter. (Our companion guide, Is an MRI safe?, covers this in depth.)

How to get ready

Most MRIs need little preparation — usually no fasting unless your clinic tells you otherwise. Wear simple clothing without metal (you may change into a gown), leave valuables at home, and arrive a little early to complete the safety form. If enclosed spaces worry you, raise it when booking — options include a wider scanner or mild sedation.^[1]

Getting your results

You won’t get results on the day. A radiologist — a specialist doctor — interprets the images and sends a report to the doctor who referred you, who’ll discuss what it means and any next steps.^[2]

A note on cost in Australia

MRI is the one scan where Medicare cover can depend on who referred you — some MRI items are only rebated on a specialist referral, others on a GP referral if criteria are met. It’s worth asking your doctor whether your MRI is Medicare-rebatable, and asking the clinic whether it’s bulk billed. (See our guide to scan costs in Australia.)

Frequently asked questions

Is an MRI better than a CT scan?

Neither is “better” — they’re suited to different things. MRI is superb for soft tissue (brain, spine, joints) and uses no radiation, while CT is faster and often better for bone detail, the chest and emergencies. Your doctor picks the one that answers the question.^[1]

Does an MRI hurt?

No. The scan is painless — you won’t feel the magnetic field. The main things you’ll notice are the loud noise (you’ll have ear protection) and having to lie still in an enclosed space.^[1]

How long does an MRI take?

Usually 15–45 minutes, sometimes longer for complex scans or multiple body parts. Your clinic can tell you roughly how long yours will take.^[1]

Can I have an MRI if I’m claustrophobic?

Usually yes, with planning. About 1 in 20 people need a mild sedative; many practices also have wider or more open scanners. Raise it when you book so the clinic can help.^[1]