MRI

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MRI scans

Magnetic resonance imaging (MRI) is a non-invasive way to take pictures of the body.

Unlike x-rays and computed tomographic (CT) scans, which use radiation, MRI uses powerful magnets and radio waves. The MRI scanner contains the magnet. The magnetic field produced by an MRI is about 10 thousand times greater than the earth's.

The magnetic field forces hydrogen atoms in the body to line up in a certain way (similar to how the needle on a compass moves when you hold it near a magnet). When radio waves are sent toward the lined-up hydrogen atoms, they bounce back, and a computer records the signal. Different types of tissues send back different signals. For example, healthy tissue sends back a slightly different signal than cancerous tissue.

Single MRI images are called slices. The images can be stored on a computer or printed on film.

MRI can easily be performed through clothing. However, because the magnet is very, very strong, certain types of metal can cause significant errors, called artifacts, in the images.

Magnetic resonance imaging; Nuclear magnetic resonance (NMR) imaging

You may be asked to war a hospital gown or clothing without metal fasteners (such as sweatpants and a t-shirt).

You will be asked to lie on a narrow table, which slides into the middle of the MRI machine. If you have a fear of confined spaces (claustrophobia), tell your doctor before the exam. You may be prescribed a mild sedative, or your doctor may recommend an "open" MRI, in which the machine is not as close to the body.

Small devices, called coils, may be placed around the head, arm, or leg, or other areas to be studied. These devices help send and receive the radio waves, and improve the quality of the images.

Certain exams require that a special dye (contrast) be given before the test. The dye is usually given through an intravenous line (IV) in your hand or forearm. The contrast helps the radiologist see certain areas more clearly.

During the MRI, the person who operates the machine will watch you from a room next door. Several sets of images are usually need, each taking from 2 to 15 minutes. Depending on the areas being studied and type of equipment, the exam may take 1 hour or longer.