MRI Stands for Magnetic Resonance Imaging. Once called Nuclear Magnetic Resonance Imaging, the "nuclear" was dropped due to public concerns about radioactivity.
MRI produces pictures of various parts of your body without the use of x-rays (unlike regular x-rays pictures & CT scans) and without the use of nuclear element injection like gallium scans. A MRI scanner consists of a large and very strong magnet in which the patient lies. A radio wave antenna is used to send signals* to the body and then receive signals back. These returning signals are converted into pictures by a computer attached to the scanner. Pictures of almost any part of your body can be obtained at almost any particular angle. (* These "radio wave signals" are actually a varying or changing magnetic field that is much weaker than the steady, strong magnetic field of the main magnet.)
How safe is MRI?
MRI is quite safe in the majority of patients and there are no documented side effects. Certain patients may not be able to have an MRI. These include people who get nervous in small spaces (claustrophobic) and those with implanted medical devices such as aneurysm clips in the brain, heart pacemakers and cochlear (inner ear) implants. Also, people with pieces of metal close to or in an important organ (such as the eye) may not be scanned. There are a few additional safety considerations and some exceptions based on individual circumstances.
Advise the scanning staff if you think you might be pregnant - because the effects of strong magnetic fields on a fetus are not well documented at this time, pregnant women are usually advised to avoid MRI scans. Also, certain metal objects that we commonly have on like watches, credit cards, hair pins, writing pens, etc. may be damaged by the MRI scanner or may be pulled away from our bodies if we go into an MRI room. Also, metal can sometimes cause poor pictures if it is close to the part being scanned. For these reasons, patients are asked to remove these objects before entering the MRI scanner.
What will I experience during the MRI examination?
You will most likely be lying on a special table that moves into the center of the magnet. Prior to going into the magnet you will be offered earplugs to reduce the noise that you hear. You will then hear some "hammering" noises while the scanner is preparing for scanning and taking the pictures. During this hammering noise, it is important not to move, as this would blur the pictures. You may also feel some vibration during the hammering noise and some slight movement of the table during the examination. Some patients will be given an injection in their arm of a substance that improves certain types of pictures. This substance, called a contrast agent, is very safe and is unrelated to the iodine used for CT scans and kidney x-rays.
What are the uses and advantages of a MRI scan other types of scans?
MRI scanners are good at looking at the non-bony parts or "soft tissues" of the body. In particular, the brain, spinal cord and nerves are seen much more clearly with MRI than with regular x-rays and CT scans. Also, muscles, ligaments and tendons are seen quite well so that MRI scans are commonly used to look at knees and shoulders following injuries. A MRI scanner uses no x-rays or other radiation. A disadvantage of MRI is it’s higher cost compared to a regular x-ray or CT scan. Also, CT scans are frequently better at looking at the bones that MRI.
Similar Tests
CT, gallium scans, and the newer PET scans may provide similar data on disease when compared to MRI scans.
Modern Advances
Advances in MRI technology have led to open MRI machines that are less confining than the tunnel type MRI machines of old. If you have a tendency for claustrophobia then see if an open MRI machine is available in your area. I had one January 2004 - went great and metal was not a problem.
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