The short answer
An MRI uses a powerful magnet and radio waves, not radiation, to take detailed picture slices of your body that can show where tumors may be. You lie still on a table that moves into a long chamber. The machine makes loud thumping and rhythmic beating noises. Sometimes a contrast dye is injected into a vein to make tumors show up more brightly.
An MRI uses a powerful magnet and radio waves to take pictures of your body in slices.
The slices are combined into detailed images that can show where tumors may be.
You lie still on a table that is pushed into a long chamber surrounding part or all of your body.
The MRI machine makes loud thumping noises and rhythmic beats while it works.
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The full explanation.
The short version
An MRI can sound intimidating before you have had one. The noise, and the idea of lying inside a machine, are usually why. Once you know what is actually happening, it is easier to feel ready for it. An MRI uses a powerful magnet and radio waves, not radiation, to take pictures of your body in slices. Those slices are combined into detailed images that can show where tumors may be.
How an MRI is different from other scans
Unlike a CT scan or an x-ray, an MRI does not use radiation. It relies on a strong magnet and radio waves to build its pictures. That is one reason your doctor may choose an MRI for certain parts of the body. The detail it captures is especially useful for seeing soft tissue clearly.
Before the scan
An MRI uses a powerful magnet, so your care team will ask you questions and give you instructions to prepare. You will likely change into a gown and remove anything metal. Ask your team ahead of time exactly what to expect for your particular scan.
During the scan
You lie still on a table. The table is pushed into a long chamber that surrounds part or all of your body, depending on the area being imaged. Staying still matters, because the machine builds detailed pictures over the course of the scan.
While the machine works, it makes loud thumping noises and rhythmic beats. This is completely normal. It is the sound of the magnet and the machine doing their job, not a sign that anything is wrong. Many people find it helps to know in advance how loud it will be, so the noise does not come as a surprise.
About the contrast dye
For some MRIs, a special dye called a contrast agent is injected into your vein before or during the exam. The dye helps tumors and other areas show up more brightly in the pictures, which gives your care team clearer information. Not every MRI needs contrast. Your doctor will let you know whether yours does.
Getting through the noise and stillness
Lying still inside a chamber, with loud noises happening around you, can feel like a lot to manage. It can help to know in advance roughly how long your scan will take. Ask your team about anything they offer to make it more comfortable, such as talking to you through the process. Some people find it helps to close their eyes and focus on breathing steadily.
After the scan
Once the scan is complete, you can usually resume your normal activities. Your care team will tell you if anything is different for you. If you had contrast dye, ask whether there is anything specific to do afterward.
Questions for your team
Before your appointment, ask whether you will need contrast dye. Ask roughly how long the scan will take. Ask what part of your body will be inside the machine. Knowing these details ahead of time can make the whole experience feel far less unfamiliar.
Words to know
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Common questions
Will an MRI be loud?
Yes. The MRI machine makes loud thumping noises and rhythmic beats while it takes pictures. This noise is a normal part of how the machine works.
What does an MRI actually do?
An MRI uses a powerful magnet and radio waves — not radiation — to take pictures of your body in thin slices. Those slices are combined into detailed images that can show where tumors may be.
What is the machine like during the scan?
You lie still on a table that is pushed into a long chamber that surrounds part or all of your body, depending on what area is being imaged.
Will I need an injection for my MRI?
Sometimes. A special dye, called a contrast agent, may be injected into your vein before or during the exam to make tumors show up more brightly in the pictures. Not every MRI requires this.
Questions to ask your doctor
Being prepared helps you get the most out of your appointments. Save or print these questions.
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Your next step
Get ready with a checklist and questions for the visit.
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Last updated: 2026-08-10Next planned review: 2027-07-14
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How this page was created
Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes. We do not employ clinicians and do not intend to — our work is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status: Source checked — This page was written with AI assistance and checked line by line against the sources listed on it. That confirms the sources support what the page says. It is not a medical review, and it does not confirm the page is complete or right for your situation.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
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