MRI Scans - FAQ
Written by Dr Joy Yip - BSc (Med) MBBS (UNSW) MPH (USYD)
What does MRI stand for?MRI stands for magnetic resonance imaging. It has been used in medical imaging since the 1980’s. It involves the production of a magnetic field that causes hydrogen atoms in the body to align in a certain direction. When the field is switched off, the atoms return to their normal alignment sending off a signal that can be interpreted by a computer to produce images.
How much radiation is there from an MRI scan?None that you need to worry about. There is no ionising radiation from an MRI scan as it uses magnetic and radio waves. This means that there is no increased risk of cancer and it is theoretically safe in pregnancy. This does not mean it is safe for everyone! Because a powerful magnetic field is created, people with metal implants should check if they are suitable for MRI scans as the magnetic field could dislodge metal parts depending on their size and location. Also, MRI scans can cause pacemakers or defibrillators to malfunction with potentially disastrous and lethal consequences.
Who should not have an MRI?People with the following:
- Brain aneurysm or haemostatic clips - may dislodge
- Cardiac pacemaker or cardiac defibrillator - may malfunction
- Cochlear implants - may move or malfunction
- Insulin pumps - may malfunction
- Metal shrapnel / bullets / shavings - may dislodge
- Metal splinters in the eye - may dislodge
- Claustrophobia / panic attacks*
*An MRI scan requires a person to lie perfectly still in a dark enclosed space for a considerable period of time. The loud knocking and banging noise produced by the magnetic coils are distressing for some people.