Magnetic Resonance Imaging

Introduction

MRI or magnetic resonance imaging scan is an imaging test that creates pictures of internal body structures (bones and soft tissues) with the help of magnetic fields and radio waves.

The MRI can also be combined with other imaging techniques to provide a more definitive diagnosis. The scan is often used to clarify findings from previous X-rays or CT scans.

Indications

MRI scans provide information on a variety of conditions and procedures and to assess function of the internal organs such as:

• Brain and spinal cord abnormalities
• Prostate, liver and breast abnormalities
• Function and structure of the heart
• Joint problems
• Blood flow through blood vessels
• chemical composition of tissues
• Tumour detection and help in staging (tumour size, severity and spread)

Procedure

Before the procedure you will be asked to remove any metallic devices such as hearing aids, hairpins, removable dental work or other objects that may interfere with the procedure. You may be provided with ear plugs or music to block the strong noises from the MRI scan. You may be sedated if required.

The MRI machine consists of a large strong magnet and a table that moves into the opening of the scanner. During the procedure you will be asked to lie on the table, which will be advanced into the scanner. The machine creates a magnetic field that creates loud noises. In some cases, a contrast dye may be injected through your arm to provide a clearer view of the scan. A radio wave antenna directs signals to the body and receives them back to create images by a computer attached to the scanner. You need to keep very still throughout the scan as movement may blur the resulting images. The entire procedure may take up to an hour to complete.

If you were not sedated, you may resume your usual activities immediately after the MRI. If you have been given a sedative, you will need to arrange for a relative or friend to take you home after the scan.

Advantages & Disadvantages

Advantages of MRI include:

• Does not use radiation
• Is non-invasive
• Can take images of any part of the body from almost any direction and orientation
• Produces better images of soft-tissue structures compared to other imaging techniques
• Can differentiate between tissues based on their biochemical properties such as water, fat, iron
• Can scan large regions of the body

Disadvantages of MRI include:

• Certain patients who get nervous in small spaces (claustrophobic) may not be able to have an MRI.
• Elderly or ill patients may find it difficult to cooperate, which may result in blurred images.
• MRI cannot be done on patients with implanted medical devices such as aneurysm clips in the brain, heart pacemakers and cochlear (inner ear) implants
• MRI is an expensive procedure

Risks and complications

Since an MRI scan is a non-invasive test, it is a very safe procedure. However, there is a very small risk of an allergic reaction to the contrast dye or sedation medicine if used. Any metal or electronic devices in your body are a safety threat and you should not undergo an MRI in those circumstances. Before your MRI test, make sure you notify your doctor and the MRI technologist if you:

• Have any health conditions, such as kidney or liver problems that may prevent you from having an MRI using contrast material
• Are pregnant as the effects of magnetic fields on the baby are not yet known