What is MRI (Magnetic Resonance Imaging)?

MRI is a non-invasive procedure that uses powerful magnets and radio waves to construct pictures of the body. MRI imaging is based on the magnetic properties of atoms. A powerful magnet generates a magnetic field roughly 10,000 times stronger than the natural background magnetism from the earth. A very small percentage of hydrogen atoms within a human body will align with this field. When focused radio wave pulses are broadcast towards the aligned hydrogen atoms in tissues of interest, they will return a signal. The subtle differences in that signal from various body tissues enables MRI to differentiate organs, and potentially contrast benign and malignant tissue. Any imaging plane (or "slice") can be projected, stored in a computer, or printed on film. MRI can easily be performed through clothing and bones. However, certain types of metal in the area of interest can cause significant errors in the reconstructed images.

How is the Procedure Performed? 

Since MRI makes use of radio waves very close in frequency to those of ordinary FM radio stations, the scanner must be located within a specially shielded room to avoid outside interference. The patient will be asked to lie on a narrow table which slides into a large tunnel-like tube within the scanner.

In addition, small devices may be placed around the head, arm, or leg, or adjacent to other areas to be studied. These are special body coils which send and receive the radio wave pulses, and are designed to improve the quality of the images. If contrast is to be administered, an IV will be placed, usually in a small vein of the hand or forearm. A technologist will operate the machine and observe you during the entire study from an adjacent room.

Several sets of images are usually required, each taking from 2 to 15 minutes. A complete scan, depending on the organs studied, sequences performed, and need for contrast enhancement may take up to one hour or more. 

There is no pain. The magnetic field and radio waves are not felt. The primary possible discomfort is the claustrophobic feeling that some experience from being inside the scanner. The table may be hard or cold, but you can request a blanket or pillow. The machine produces loud thumping and humming noises during normal operation. Ear plugs are usually given to the patient to reduce the noise.

A technologist observes the patient during the entire procedure and may be spoken to through an intercom in the scanner. Some MRI scanners are equipped with televisions and special headphones to help the examination time pass.

Excessive movement can blur MRI images and cause certain artifacts. If the patient has difficulty lying still or is very anxious, an oral or intravenous sedative may be given. There is no recovery time, unless sedation was necessary. After an MRI scan, you can resume normal diet, activity, and medications

Where is MRI Performed?

The Calgary Health Region operates MRI units at the Foothills Medical Centre , the Rockyview, Peter Lougheed and Alberta Children's Hospitals and the South Calgary Health Centre.