MRI

Definition

Magnetic resonance imaging (MRI) is a scanning technique that provides pictures of the body without using ionising radiation (x-rays).

MRI makes use of powerful magnets and radio waves.

The magnetic field forces the body’s hydrogen atoms to line up in one direction. Radio waves are then sent in and the hydrogen atoms are knocked out of sync. As the hydrogen atoms re-align in the magnetic field they emit a signal. Different types of tissues emit different signals, which give different tissues their own different appearance.

How the test is performed

You will be asked to wear a gown. This is done so that any metal buttons or clips on your clothing are not brought into the scanner.

You will be positioned on a narrow table, which glides into the aperture of the MRI machine. At DiagnostiCare, the doughnut of the MRI is only 1.2 meters deep and most scans are performed with your head well out of the scanner. You will also be offered the choice of video or music to keep you pre-occupied whilst you are on the scanner. But if you fear confined spaces (i.e. claustrophobia), please tell your doctor before the exam. Your doctor may prescribe you a mild sedative

Small devices, called coils, may be positioned around the body part that is being studied. These coils are receivers which enhance the picture quality.

A contrast may be given before certain MRI tests through a vein in the back of your hand or your forearm. The contrast helps the radiologist demonstrate certain areas more clearly.

Whilst the scan is being done, the radiographer will be seated at the console, which is separated from the MRI room by a door and a glass window. The radiographer will talk to you and listen to you on an intercom system, and will be able to see you all the time. Usually, different kinds of images are needed, each type taking 3- 15 minutes. Depending on the areas being studied, the exam could take from 30 minutes to an hour.

How to prepare for the test

Preparation depends on the area being examined.

Some scans require no food or drink for 4 – 6 hours prior the scan. No other preparation is usually needed.

The magnetic fields encountered during an MRI scan may interfere with certain implants, in particular, pacemakers. Any patient who has a cardiac pacemaker cannot have an MRI, and indeed, is not allowed into the MRI scanning area.

MRI examination may not be possible if you have any of the following metallic objects in your body:

  • Aneurysm clips in the brain
  • Certain prosthetic/artificial heart valves
  • Inner ear (cochlear) implants
  • Recently placed joint replacements
  • Certain older types of vascular stents

Please tell your doctor and the DiagnostiCare MRI booking personnel if you have one of the above devices prior to, or at the time of booking the test, so the precise type of metal can be determined.

Prior to an MRI being done, metal workers or people who have been exposed to metal fragments, must have a skull x-ray to make sure that there are no metal fragments in the eyes.

No metal objects are allowed into the scanning room.

It is important to stress that people have been harmed in MRI machines in cases where they have not removed metal objects from their clothes, or when metal objects have been taken into the room by others.

How the test will feel

MRI causes no pain. A small percentage of patients may become anxious on the scanner. If you are an anxious person or find it difficult to lie still then, a mild oral sedative may be appropriate.

If you move on the scanner, then the images may become blurry.

You may request a blanket it you feel cold.

The MRI machine sound a bit like a jack-hammer and produces a thumping sound and humming noises when switched on. At DiagnostiCare we have various distraction options for you to choose from (music/video), and which will make the test as comfortable as possible.

You can go home as soon as the study is completed, unless you have been given sedation, in which case we will monitor you for a specified period after the scan. After the MRI scan, you can resume your normal diet, activity, and medications.

What the risks are

MRI contains no x-rays or ionising radiation. To date, no documented significant side effects of magnetic fields and radio waves have been described on the human body.

The most frequent type of contrast used is Gadolinium. It is very safe. Allergic reactions to the substance very rarely occur. It is avoided in patients with significantly abnormal renal function. The MRI radiographer will monitor your heart rate and breathing as needed.