The MRI scanner sends the signals to a computer, which manages the information and creates a 3-D image of the scanned tissue. The image then prints on photographic film or videotape. MRI scans can penetrate bone and provide clear, detailed pictures of tissues and muscles. In preparation for the MRI, the patient lies on a narrow table that slides inside a large tunnel-like tube. The scanner then surrounds the patient with a magnetic field. A radiologist who specializes in MRIs examines the film or computer for abnormalities.
People who are claustrophobic, agitated, or disturbed by the loud noise may be given an anti-anxiety medication before the examination. Additionally, ear plugs may be used, and are oftentimes provided by the MRI center. Sometimes hospitals use open MRI machines that are less noisy and not as confining as the closed models but have other limitations.
The MRI technique operates on the principle that the most abundant atom in the body is hydrogen, which is present in every water molecule. When placed in a powerful magnetic field, such as that of an MRI machine, the nuclei of these hydrogen atoms line up in one direction, just as compass needles point to the poles of the earth's magnetic field. When energy from radio waves is directed into the field of the body part that is being examined, the nuclei are temporarily moved out of alignment. When the radio waves stop, the nuclei return to their alignment, giving off their own energy in the process. The machine's computers record the duration and intensity of these signal changes and convert the data into information that produces a series of images, showing the internal structure of the examined part. An MRI usually costs about $1,000 or more per examination, and the machines themselves are prohibitively expensive for small hospitals or rural areas. In many cases, a less expensive test may be ordered prior to obtaining an MRI. Patients should discuss this with their physicians.
Last updated: 06-Jun-07