What is an MRI scan?
Magnetic Resonance Imaging (MRI) is a type of scan used to look inside the body. It uses magnetic fields and radio waves which are used by a computer to create images of any part of the body. It is able to look at soft tissues that x-rays cannot see in detail, and also the internal structure of bones, muscles and other structures from any angle. It can define injury to these structures and differentiate between normal and abnormal tissues better than almost any other type of scan. Because of this, it has become one of the most widely used techniques for diagnosing sports injuries, and monitoring their response to treatment. It is used on all elite athletes to diagnose injury, guide treatment and determine fitness to play.
Can everyone have an MRI scan?
Although MRI is harmless, the use of strong magnetic fields means certain patients cannot have a scan: Patients with pacemakers, certain types of artificial heart valve, cochlear implants (a device used to help certain deaf people hear), internal nerve stimulators and internal pump devices cannot be scanned, as the magnet can damage them. People who have had certain types of surgery cannot be scanned for up to 6 weeks after their operation (or sometimes at all). People who have had metal injury to the eyes (welders or angle grinders) and people with shrapnel injury to any part of the body may require an x ray before the scan to see if they will be safe. People who have had most types of surgery can be scanned and this includes joint replacements or metalwork placed in the body to help bones heal, or in the spine. MRI has been used safely for over 20 years but pregnant women are not routinely scanned as a precaution, because the long term effects of a scan on the developing baby are not yet known.
People scheduled for a scan should not wear jewellery, including watches, and should remove any body piercings they have. People who have tattoos should let the technician know of this as the tattoo site can become warm in the scanner. Before the scan, a questionnaire is filled out by the patient to ensure none of the above conditions apply for complete safety.
How is an MRI scan performed?
The MRI scanner is comprised of a tube roughly 2 meters long into which the patient is placed. The part of the body being scanned is then covered with an “aerial” which picks up the signal created by the scanner to turn into images on the computer. The pictures take roughly 20-30 minutes to be created during which the patient is asked to lie as still as possible to prevent the pictures from becoming blurred. Sometimes a special dye is used to gain more information about the tissue being scanned.
The scan is entirely painless, and there are no known harmful effects on the body. Usually no special preparation is required before the scan. During the time in the scanner, the patient is in constant contact with the technicians performing the scan via an intercom, and the scan can be stopped at any time for any reason. The scan can be quite noisy, but the patient is provided with special headphones to protect the ears, and allow them to listen to the radio or a CD to pass the time (Many patients bring their own music).
After the scan, the patient can go home and return to normal activities. The pictures are then reviewed by a Radiologist (a doctor specially qualified to interpret the images) who issues a report for the specialist. This normally takes 1-2 days.
MRI scan of a shoulder joint (compare with CT and Ultrasound pictures in the relevant pages). Muscle and tendon can be seen in great detail. Certain types of inflammation are best seen on MRI. Bone injuries are also well seen, although CT may be better in some situations. MRI can see deeper into soft tissues than ultrasound, but cannot routinely image joint structures whilst they are moving.