Magnetic Resonance Imaging (MRI)

inside an mri machine
photo by Remco Frank

Magnetic Resonance Imaging (MRI) is a type of test that uses magnetic fields rather than radiation to take pictures of a patient's internal organs. An MRI machine is built with many electrical coils, which create changing magnetic fields. A radio antenna detects the changes in these magnetic fields and sends this information to a computer, which changes the information into an image.

Because it doesn't use any radiation, MRI is very safe for most patients. Of course, all metal must be removed from the body – this includes body piercings and jewelry – prior to the scan. Patients with metal implanted into their body or with pacemakers may not be able to receive a scan. The magnetic field is very strong, so metal may react to it.

Like a CT scan, some patients may receive an injection of a "contrast agent". This dye helps doctors view the internal organs more clearly. Iodine is usually used, and it rarely has any serious side effects. A feeling of warmth is typical when the dye is injected, but this goes away quickly.

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.

Patients should be aware that the MRI machine is very loud. Physicians usually provide earplugs, but the noise can still be overwhelming.

Also, because the patient lies in a small tube, there is a chance of claustrophobia. If a patient knows they suffer from claustrophobia, they may be knocked out with anesthesia prior to the scan. Another option is to have an open MRI, which uses an open area to perform the scan instead of a small tube.

Why MRI?

Magnetic resonance imaging is great for looking at the soft tissue in a body. This includes all of the internal organs – heart, lungs, liver, etc. – and the blood vessels. Though it is not as good at imaging bone.

Similar Tests

CT, gallium scans, and the newer PET scans all provide similar data for the diagnosis of cancer.

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 CT 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 it’s higher cost compared to a regular x-ray or CT scan. Also, CT scans are frequently better at looking at the bones that MRI.

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