MRI is a relatively new form of diagnosis using powerful magnetic fields and radio waves producing images of internal organs with a much greater soft tissue contrast than that offered by conventional CT scanners.
Despite intensive research (and in contrast to ionising radiations) there is no evidence to suggest any dangers to patients or associated clinical staff from the radio waves. There is, however, a requirement for electromagnetic shielding commonly known as RF shielding to block external radio frequency interference which may adversely affect the image quality. This is in the form of a six sided ‘box’ (Faraday Cage) constructed from electrically conductive materials.
The Faraday Cage serves two purposes:
- to isolate the scanner from outside interference
- to stop the radio frequencies produced by the scanner from interfering with equipment outside the cage e.g. monitoring equipment
In some instances magnetic shielding will also be required to contain the magnetic fringe field within the room in order to minimise the risk to people and also avoid disturbance to sensitive medical equipment. It also performs the function in reverse where large ferrous metal objects such as excessive road traffic or lift shafts are in the immediate location which may cause interference and affect the quality of the scanner images.
This type of shielding is achieved using low carbon steel or any other suitable ferrous metal.
RF shielding generally follows a standard pattern for all MRI scanners. However, the extent and thickness of magnetic shielding involves detailed calculations based on the strength and position of the magnet within the room, room size and an assessment of any potential outside interference.
These calculations are usually available from the equipment manufacturers or the shielding suppliers.
We also offer this service via our Consultant Radiation Protection Advisor (RPA). Please refer to full details of our RF cage facilities.