A magnetic resonance imaging scan is usually called an MRI. An MRI does not use radiation (X-rays) and is a noninvasive medical test or examination. The MRI machine uses a large magnet and a computer to take pictures of the inside of your body. Each picture or "slice" shows only a few layers of body tissue at a time. The pictures can then be examined on a computer monitor.
Pictures taken this way may help caregivers find and see problems in your body more easily. The scan usually takes between 15 to 90 minutes.
A substance called gadolinium is injected into a vein to help the physicians see the image more clearly. The gadolinium collects around cancer cells so they show up brighter in the picture. Sometimes a procedure called magnetic resonance spectroscopy (MRS) is done during the MRI scan. An MRS is used to diagnose tumours based on their chemical make-up.
How does MRI works?
The MRI machine is a large, cylindrical (tube-shaped) machine that creates a strong magnetic field around the patient. This magnetic field, along with a radio-frequency, alters the hydrogen atoms' natural alignment in the body.
A magnetic field is created and pulses of radio waves are sent from a scanner. The radio waves knock the nuclei of the atoms in the body out of their normal position; as the nuclei realign back into proper position, they send out radio signals.
These signals are received by a computer that analyses and converts them into an image of the part of the body being examined. This image appears on a viewing monitor. Some MRI machines look like narrow tunnels, while others are more open.
MRI may be used instead of a CT scan in situations where organs or soft tissue are being studied, because with MRI scanning bones do not obscure the images of organs and soft tissues, as does CT scanning.