**3.4. Colour and symbol coding**

Various means have been adopted to help with ensuring safety in an MRI unit. This is usu‐ ally meant to provide on the spot recognition of MR- safe equipment and surroundings, likewise unsafe and MRI-conditional equipments and locations. At the University of Califor‐ nia San Francisco (2011), yellow is used to signify caution and is painted around the en‐ trance of the door. Gas tanks that have been painted green signifies ferrous cylinder and hence make it easy for identification as MRI unsafe equipment. For safe MRI tanks, the cyl‐ inders are coloured silver. Symbols have also been used as a new classification system for implants and ancillary clinical devices.

An MRI safe symbol signifies that the device or implant is completely non-magnetic, nonelectrically conductive, and non-RF reactive, eliminating all of the primary potential threats during an MRI procedure. An MRI Conditional sign is used to identify a device or implant that may contain magnetic, electrically conductive or RF-reactive components that is safe for operations in proximity to the MRI, provided the conditions for safe operation are defined and observed (such as 'tested safe to 1.5 teslas' or 'safe in magnetic fields below 500 gauss in strength). Finally, an MRI unsafe symbol is reserved for objects that are significantly ferro‐ magnetic and pose a clear and direct threat to persons and equipment within the magnet room. An appropriate coding system is thus necessary to be adopted by every MRI unit to facilitate easy identification of safe items.
