Magnetic resonance imaging (MRI) is one of the most technologically advanced diagnostic tools available. MRI uses a powerful magnet, low intensity radio frequency pulses and computer technology to create detailed images of the soft tissues, muscles, nerves and bones in your body. In many instances, it replaces the need for X-rays, hospitalization and exploratory surgery. There are no known side effects of MRI, and it uses no radiation.
How MRI Scanners Work
The main component of the MRI scanner is a magnet. This magnet causes your body's hydrogen atoms to align themselves in such a way as to receive radio signals from the magnetic resonance system. When your body receives these signals, it reacts by sending its own radio signals back to the machine. It is this radio frequency transmitted by your body that is computer-processed and turned into highly detailed images.
Types of MRI Scans
There are two types of MRI scanners, high-field and open configuration. With a high-field MRI, the bore (chamber) in which you lie is cylindrical, and the body part to be examined is placed in the center of the magnet. Open configuration MRI systems have larger openings to accommodate larger and claustrophobic patients. The main functional differences between open and high-field MRI is the strength of the magnet. The magnet in a high-field MRI is stronger than that of the open unit. The stronger the magnet, the better the image quality and the greater the speed of the scan.
Understanding Contrast Media
Certain types of MRI scans require the use of a safe paramagnetic agent or contrast media. This contrast media, which is given during the exam, enhances blood vessels and highlights certain body parts. The Food & Drug Administration (FDA) has requested manufacturers of gadolinium based contrast add additional warnings to their product labels. To read the FDA warnings regarding gadolinium contrast agents follow this link and view "The Information for Healthcare Professionals" document. You should receive complete instructions concerning the use of a contrast agent from your physician when he or she orders the test. Tell your physician before your exam if you have ever had an adverse reaction to contrast media. If a contrast agent is used, it is recommended you not eat or drink anything for two hours prior to the exam.
During the Exam
While the MRI test is being conducted, you will lie on a scanning bed with the body part of interest placed in the center of the magnet. If you are having a high-field MRI, the inside of the magnet chamber is cylindrical. If you are having an open MRI, the magnet opening is larger and rectangular shaped. Often times, a family member or friend may accompany you during the exam.
Your technologist will conduct the test from an adjacent room. You will be able to communicate with your technologist through a patient intercom system during the entire exam. You should remain relaxed and as still as possible. You will hear a knocking sound from the MRI system that ranges from barely audible to quite noticeable. Hearing protection or headphones will be provided when necessary. Most exams take 30-to-40 minutes to complete, and you may resume normal activities afterward.
A radiologist will interpret your exam, and the results will be sent to your physician as soon as possible.