Magnetic Resonance Imaging (MRI) allows different types of tissues inside the body to be seen with great clarity, including disks, muscles, and tendons.

MRI utilizes magnetic fields, radio waves and computer algorithms to produce high-resolution cross-section images of the human body.

Here's how it works. First, the very powerful magnet used in MRI technology aligns the spin angles of hydrogen atoms in the body. Then a low-power radio-frequency pulse is transmitted, perturbing the hydrogen atoms and altering their spin direction and resonant frequency. When the radio signals are halted and the hydrogen atoms return to their aligned state, the stored energy from the initial radio signal produces a faint radio wave that, when analyzed by a computer, can be transformed into detailed images of the body's interior with image resolutions of a millimeter or less.

Altering the local magnetic field in the specific tissue being examined produces variations in the stored-energy radio waves, depending on the type of tissue.

It is this contrast in wave frequency that allows a radiologist to distinguish between normal and abnormal tissue.

Diagnosis

MRI is used for a variety of diagnoses, including spine and joint problems, sports injuries, coronary disease and heart damage, and cancer detection. Because an MRI involves no radiation exposure, it is often used in place of traditional X-rays or CAT scans when radiation exposure might pose a risk to the patient.

Your Exam

Because the magnets used in the MRI procedure are extremely powerful, you will be required to remove any metal objects before entering the exam room. And if you have metal inside your body, such as a pacemaker, metal fragments or orthopedic devices, other imaging techniques will probably have to be used to make a diagnosis.

Some patients also experience anxiety or claustrophobia as a result of being confined in the small space of the magnet's bore. Being required to lie very still (which is necessary to obtain a clear image) can heighten this anxiety. An MRI unit also emits a number of sounds while the procedure is taking place. If small spaces or loud noises make you uncomfortable, you should ask your doctor for medication to help you relax during the examination. New open MRI technology also helps lessen this claustrophic effect.

For more information about MRI, visit the American College of Radiology/Radiological Society of North America Web site.