AUA Summit - What is an MRI?


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What is Magnetic Resonance Imaging (MRI)

Magnetic resonance imaging (MRI) uses radio waves and magnets to make detailed pictures of the body's organs and soft tissues. These images can be seen in 3-D (3 dimensions).

How is MRI unlike Other Tests?

  • MRI does not use ionizing radiation (unlike X-rays or CT scans).
  • MRI clearly shows differences between normal and diseased tissues. The images are clearer than with CT.
  • MRI does not typically need a dye for contrast (like with CT). This is good if you have kidney problems.
  • With MRI, certain settings will show different types of tissue. This can help to more accurately make a diagnosis.

When is it Used?

MRI can be tailored to help answer almost any clinical question. It can show soft tissues in great detail. It can spot masses and cystic structures. It can clearly show blood vessels and lymph nodes.

For example, if a mass is found in the kidney, MRI can tell the difference between a hollow cystic mass and a solid mass. It can show clear 3-D images of its shape. Based on 3-D MRI images, a urologist or radiologist can see if a mass is cancerous or benign (not cancerous).


This test is done in a hospital radiology department or in a health care provider’s office by a technician, supervised by a doctor.

You will be asked to lie on a narrow table. Your head will be placed in a padded plastic cradle or on a pillow. This table will slide into a large tunnel-like tube in the scanner, and you will be told to breathe quietly and normally but to stay very still.

Lying inside a large, hollow magnet, you will be exposed to radio waves. This energy is directed at water molecules in the body, "exciting" and then "relaxing" the protons in water molecules.

The MRI reads the energy from the water molecules and builds a 3-D image of the different types of tissue.

MRI often involves taking many sets of images, each lasting about 2 to 15 minutes.

Some people don’t feel comfortable in close or confined spaces. For this test, you do have to lie still on a hard table inside a narrow tube. If you have a history of anxiety or fear of closed spaces, you should talk to your doctor. You may be able to take a drug to relax you before the test. No other preparation is needed.

The technician will be able to talk to you during the test through an intercom. While the scanner is working, you will hear rapid, loud noises coming from the walls of the scanner. You may be given earplugs to help with the noise.

To get clearer images, your doctor may decide you may need an IV placed for gadolinium contrast.


If you are generally healthy, there is little to no risk with MRI. This test cannot be done if you have any metal in your body, such as:

  • Metal hip/knee/joint replacements
  • Cardiac pacemaker/defibrillator or other implanted devices
  • Brain aneurysm clips/coils
  • Ear implants

The technician or doctor will ask if you have any metal in your body to prevent trauma or burn with an MRI.


MRI does not work very well in the urinary tract. Its signals will not show calcifications in soft tissue and bladder abnormalities.

Also, MRI does not show bones clearly, so it’s less useful if your doctor is trying to see if cancer has spread to the bone.

MRI is very useful when gadolinium contrast is added. This results in much more detail for soft tissue than CT scans. But this should not be used if you have kidney or liver problems.

After the Test

The whole test takes about 30 to 60 minutes. After the test you can go back to your normal daily activities.

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