MRI: Thermal burns
Advanced, Generic Clinical Sciences, Special Problems or Issues in Anesthesiology
It is generally understood that direct electromagnetic induction in looped cables associated with the patient are responsible for the excessive heating, and it is on this theory that present guidelines are based.
MR systems require the use of RF pulses to create the MR signal. This RF energy is transmitted readily through free space from the transmit RF coil to the patient. When conducting materials are placed within the RF field, the result is a concentration of electrical currents sufficient to cause excessive heating and tissue damage. The nature of high frequency electromagnetic fields is such that the energy can be transmitted across open space and through insulators; therefore, only devices with carefully designed current paths can be made safe for use during MR procedures.
Updated definition 2020:
MRI requires radiofrequency pulses to create the MR signal, and therefore the desired image. If there are conductive materials placed near the RF field, that material can concentrate the electrical currents from the radiofrequency pulses to generate enough heat to cause severe burns.3 This most commonly happens when conductive surfaces are looped or coiled, and electrical currents cycle in a continuous path. Insulating conductive surfaces via padding, or displacing from skin may not be enough to prevent thermal burns, so it is best practice to avoid burns by ensuring no ferrous material enters the MRI suite. 4
Dempsey MF, Condon B. Thermal injuries associated with MRI. Clin Radiol 2001;56:457-65.