What is MRI?
A non-technical explanationÖ
MRI Stands for Magnetic Resonance Imaging; once call Nuclear Magnetic Resonance Imaging. The "Nuclear" was dropped off about 15 years ago because of fears that people would think there was something radioactive involved, which there is not.
MRI is a way of getting pictures of various parts of your body without the use of x-rays, unlike regular x-rays pictures and CAT 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. 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.
Also, certain metal objects that we common have on our persons 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 CAT 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 CAT 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 itís higher cost compared to a regular x-ray or CAT scan. Also, CAT scans are frequently better at looking at the bones that MRI.
BackFor more information about how MRI works, see Radiopaedia MRI physics. Please visit this excellent educational site for radiology articles and teaching file cases!
Last Modified: July 27, 2013 by Ray Ballinger.