What Is an MRI? A Simple Guide to Magnetic Resonance Imaging
Updated: Oct 29
An MRI is a medical imaging test that uses a strong magnet, radio waves, and a computer to make detailed pictures of the inside of your body. It does not use X-rays or any ionizing radiation, and the scan itself is painless. This guide explains how an MRI works, what it is used for, how to prepare, and what to expect on the day of your scan.
What does MRI stand for?
MRI stands for magnetic resonance imaging. Doctors order MRIs when they need a clear look at soft tissues, such as the brain, spinal cord, muscles, ligaments, tendons, cartilage, and organs. These tissues often don't show up well on a regular X-ray.
An MRI does not involve any cuts or needles, unless your exam uses contrast dye given through an IV. You simply lie still on a padded table while the machine takes pictures.
How does an MRI work?
Your body is mostly water, and water contains hydrogen atoms. An MRI uses those hydrogen atoms to build images. Here is the simple version:
The magnet: The MRI scanner creates a strong magnetic field that lines up the hydrogen atoms in your body.
Radio waves: The scanner sends short pulses of radio waves that briefly knock those atoms out of line.
Signals: When the radio waves stop, the atoms settle back into place and give off tiny signals.
Pictures: The scanner picks up those signals, and a computer turns them into detailed images.
Different tissues give off different signals. That is why an MRI can show the difference between healthy tissue and an injury or other problem so clearly. If you'd like a deeper look at the science, read our guide on how an MRI works.
The main parts of an MRI machine
Magnet: creates the strong magnetic field
Gradient coils: adjust the field so the scanner can image one slice of the body at a time
Radiofrequency (RF) coils: send and receive the radio wave signals
Computer: processes the signals and builds the images
The tapping and knocking sounds you hear during a scan come from the gradient coils switching on and off.
What is an MRI used for?
MRI can image almost any part of the body. Some common uses include:
Brain and nerves: tumors, multiple sclerosis, stroke, aneurysms, and other brain or nerve concerns
Spine: herniated discs, narrowing of the spinal canal, and spinal cord injuries
Joints and muscles: torn ligaments, cartilage damage, muscle injuries, and arthritis
Bones: bone infections and some injuries that are hard to see on X-ray
Abdomen and pelvis: organs such as the liver, kidneys, pancreas, and reproductive organs
Heart and blood vessels: heart structure and certain blood vessel problems
Breast: sometimes used along with mammography for people at higher risk of breast cancer
Your doctor decides which body part to scan based on your symptoms and history. For a closer look at the conditions an MRI can help find, see what an MRI scan can diagnose.
Benefits of MRI
No ionizing radiation
Unlike X-rays and CT scans, MRI does not use ionizing radiation. This makes it a good choice when someone needs repeat scans over time. Learn more in our article on why MRI scans use no radiation.
Clear pictures of soft tissue
MRI shows soft tissues in fine detail. This is why it is often used for the brain, spine, and joints.
Painless and non-invasive
There are no incisions. Most people say the hardest parts are lying still and putting up with the noise.
Is an MRI safe?
For most people, yes. The main safety concern is metal, because the MRI magnet is always on and very strong. Before your scan, the team will ask about:
Pacemakers, defibrillators, or other implanted devices
Cochlear implants or nerve stimulators
Metal pins, plates, screws, or clips from past surgeries
Any history of metal fragments, such as from metalworking
Allergies and kidney health, if contrast dye might be used
Tell your doctor and the MRI staff about any implants, even if you think they are MRI-safe. Bring any implant cards you have.
Some people feel nervous or closed in inside the scanner. If you are worried about this, talk with your doctor before your appointment. Our tips on handling claustrophobia during an MRI may also help.
How to prepare for an MRI
Clothing: Wear comfortable clothes with no metal, such as zippers, snaps, or underwire. You may be asked to change into a gown.
Metal items: Leave jewelry, watches, hair clips, and similar items at home.
Food and medicine: For most MRIs, you can eat and take your usual medicines. Some exams have special instructions, so follow what your doctor or the imaging center tells you.
Medical history: Let the team know about implants, allergies, kidney problems, or if you might be pregnant.
Paperwork: Bring your doctor's order, photo ID, and insurance card.
What about contrast dye?
Some MRI exams use a contrast agent given through a small IV. It helps certain tissues or blood vessels stand out more clearly. Your doctor decides whether your exam needs it. Tell the team if you have had a reaction to contrast before or if you have kidney problems.
What to expect during an MRI
You lie on a padded table that slides into the scanner.
The technologist may place a coil around the body part being scanned. It helps make the pictures sharper.
You get earplugs or headphones, because the machine is loud.
The technologist steps into the next room but can see you, hear you, and talk with you the whole time.
The scan is done in a series of short sets. You need to stay as still as possible during each one.
For some exams, you may be asked to hold your breath for a few seconds. If you move, the pictures can blur, and part of the scan may need to be repeated.
Time on the table depends on the body part and the type of exam, and the team can tell you what to expect for yours. See how long an MRI scan takes for more detail.
After your MRI
Most people can go back to their normal day right away. If you had contrast, the team may suggest drinking extra water.
A radiologist, a doctor who specializes in reading medical images, reviews your pictures and writes a report. That report goes to the doctor who ordered your scan, and your doctor will go over the results with you and talk about next steps.
Frequently asked questions
Does an MRI hurt?
No. The scan itself is painless. Some people feel a little uncomfortable lying still, and the machine is noisy, but you should not feel the magnet or the radio waves.
How is an MRI different from a CT scan?
MRI uses a magnet and radio waves. CT uses X-rays. MRI usually shows soft tissue in more detail, while CT is fast and very good for bones and some emergencies. Read our guide to MRI vs. CT scans to learn more.
Can I move during an MRI?
You should stay as still as you can. Even small movements can blur the images.
Do I need a doctor's order for an MRI?
If you're using insurance, yes. Your doctor's order tells the imaging team which body part to scan and why. If you pay cash (self-pay), no referral is needed at Millenium MRI, and you can call and book directly.
How long does it take to get MRI results?
At Millenium MRI, results are usually sent to your referring doctor within 24 hours. Your doctor will then share the results with you.
Related reading
Schedule an MRI at Millenium MRI
Millenium MRI has centers in Ocala, Largo, and Tamarac, Florida, and in North Little Rock, Springdale, Jonesboro, and Marion, Arkansas. Our board-certified radiologists and ARRT-certified technologists work to make your visit simple. Same-day appointments are often available, and most patients are in and out in about 35 minutes. We accept most insurance plans, workers' compensation, personal injury cases, and self-pay. Call your nearest center or request an appointment online.
This article is for general information and is not medical advice. Talk with your doctor about your specific situation.
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