30-Second Summary
An MRI uses a powerful magnet and radio waves to take pictures of the body in slices.
MRI does not use ionizing radiation, unlike CT scans and X-rays.
The detailed images can show places where there may be tumors.
During the scan you lie still inside a long chamber, and the machine makes loud thumping and rhythmic sounds.
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The full explanation.
The simple version
An MRI — magnetic resonance imaging — uses a powerful magnet and radio waves to take pictures of your body in slices. Those slices are combined into detailed images of the inside of your body, which can show places where there may be tumors.
One important difference from a CT scan or X-ray: an MRI does not use ionizing radiation. It makes its pictures with a magnet and radio waves instead.
What to expect
When you have an MRI, you lie still on a table that is pushed into a long chamber that surrounds part or all of your body. The machine makes loud thumping noises and rhythmic beats while it works. The scan does not hurt, but holding still matters, because movement can blur the images.
Contrast dye
Sometimes a special dye, called a contrast agent, is injected into your vein before or during the exam. This dye can make tumors show up more brightly in the pictures, helping your care team see them more clearly.
How MRI fits with other tests
Like other imaging tests, an MRI is one piece of the picture. Its images are read alongside your lab tests and, in most cases, a biopsy — which is often the only way to tell for sure if you have cancer. Your doctor decides when an MRI is the best tool and explains what the results mean for you.
Words to know
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Common questions
▸What is an MRI?
An MRI (magnetic resonance imaging) uses a powerful magnet and radio waves to take pictures of your body in slices. These slices are combined to create detailed images of the inside of your body, which can show places where there may be tumors.
▸Does an MRI use radiation?
No. Unlike CT scans and X-rays, an MRI does not use ionizing radiation. It creates its images using a strong magnet and radio waves instead.
▸What does an MRI feel like?
When you have an MRI, you lie still on a table that is pushed into a long chamber that surrounds part or all of your body. The machine makes loud thumping noises and rhythmic beats during the scan. It does not cause pain, but staying still is important for clear pictures.
▸Will I be given a contrast dye?
Sometimes. A special dye, called a contrast agent, may be injected into your vein before or during the exam. This dye can make tumors show up more brightly in the pictures. Your care team will let you know if you need it.
▸How is an MRI different from a CT scan?
Both create detailed pictures of the inside of the body, but they work differently. A CT scan uses X-rays (a form of radiation) and a computer, while an MRI uses a magnet and radio waves and no radiation. Your doctor chooses the scan that will best answer the question at hand.
Questions for your care team
Consider bringing these to your next appointment.
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