White-Wilson Medical Center

MRI MRI

What Is Magnetic Resonance Imaging (MRI)?

Magnetic Resonance Imaging, or MRI, is a painless and safe diagnostic procedure that uses a powerful magnet and radio waves to produce detailed images of the body's organs and structures, without the use of X-rays or other radiation.

A computer converts signals from the MRI scan into extremely clear, cross-sectional images of the part of the body that has been scanned. Each image is a slice of the body area scanned, and numerous images are created that clearly show all the features of that particular part of the body.

The images produced by MRI can be compared to a sliced loaf of bread. Just as you can lift each individual slice from the loaf and see both the slice and the inside of the bread, so too the image "slices" produced by the MRI show the exact details of the inside of the body.

The computer is able to reconstruct all the images into a single image resembling an X-ray. This reconstruction also can be made into three-dimensional images, allowing complete and remarkable visualization of the body area scanned from all angles. MRI is arguably the greatest advance in diagnostic medical techniques over the past century.

How Does Magnetic Resonance Imaging (MRI) Work?

Unlike CT, or computed tomography-another type of imaging-MRI uses no radiation. Instead, MRI uses a powerful magnet and radio waves to produce high-quality, cross-sectional pictures of the part of the body being studied. Each picture represents a virtual slice through the part of the body being imaged.

The MRI scanning machine is a large donut-shaped magnet with a sliding scanning table. A person lies on this table, which then slides into the desired position in the MRI magnet.

In our bodies, the nuclei of hydrogen atoms (called protons) normally point randomly in different directions. However, when exposed to the magnetic field in an MRI chamber, the nuclei line up in parallel formation, like rows of tiny magnets. Nearly two-thirds of the body's hydrogen atoms are found in water and fat molecules.

When the nuclei are subjected to a strong but harmless (and painless) pulse of radio waves from the MRI machine, they are knocked out of their parallel alignment. As they fall back into alignment, they produce a detectable radio signal.

The signal is recorded by the machine and transferred to a computer.

The computer uses these signals to calculate an image that is based on the strength of signal produced by different types of tissue. For example, tissues that contain little or no hydrogen (such as bone) appear black. Those that contain large amounts of hydrogen (such as the brain) produce a bright image.

How Safe Is MRI?

Because MRI does not involve the use of X-rays, it is safe for the majority of people. Certain people, however, may be unable to undergo the procedure. These include:

  • Those who have implanted medical devices, including heart pacemakers and inner ear implants.
  • Those with metal close to or in an important organ, for example a piece of metal in the eye possibly from an old injury, or metal clips in the brain following treatment for a brain aneurysm.

The reason for these limitations is that the powerful magnetic field of the scanner may interfere with the internal mechanism of some of these medical devices, which may be dangerous, as well as the fact that the presence of metal will cause poor quality pictures if it is near the part being scanned.

While there are no known hazards, MRI is not proven to be safe during pregnancy.

How Do I Prepare For A MRI?

The MRI scanner is located in the White-Wilson NeuroScience Center, on Hospital Drive across the street from the main campus.

Map & Directions


Under certain conditions, specialized MRIs that require an injection or ingestion of a contrast agent may require dietary restrictions provided by your physician. These include fasting for 8 hours prior to an MRI of the abdomen or MRCP.

You can wear regular clothing as long as it is free of metal (zippers, buttons, etc). You must remove all metal objects, including jewelry, and electronic devices (such as a watch), as these will interfere with the test and may be damaged by the strong magnetic field within the MRI scanner.

The technician will prepare you for the procedure and take you to the scanning table, which resembles a narrow bed, and position you for the test.

Before the MRI begins, the table is moved to the doughnut-shaped magnet. After the machine is adjusted, the MRI begins.

During the procedure, you will hear several series of pulsing noises. These noises are harmless and simply indicate that the machine is working. It is particularly important to remain completely still during these sequences of noises, as the MRI machine is obtaining images at these times.

If the first pictures are motion-free, it will shorten the total exam time and prevent delays.

An entire MRI exam may take from 20 minutes to 1.5 hours, depending on the type of information required by the radiologist and your physician, and the quality of the images they need to make a diagnosis.

Need To Know

The images are taken in 'sets' lasting anywhere between a few minutes to 15 minutes for each set. The technician will usually tell you when each new set commences. You need to lie still during these sets so that we are able to capture a high quality image.

If your doctor prescribes you a tranquilizer or sedative for the MRI, please make sure you have someone to drive you home from your procedure. .

What Should You Do After the Test?

After the images are obtained, you can resume normal activities immediately.


Fully Accredited By ACR

White-Wilson Medical Center is fully accredited by the American College of Radiology.