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.
In general, magnetic resonance (MR) imaging is considered to be a relatively safe diagnostic modality; however, the use of radiofrequency coils, physiologic monitors, electronically-activated devices, and external accessories or objects made from conductive materials has caused excessive heating, resulting in burn injuries to patients undergoing MR procedures. Heating of implants and similar devices may also occur in association with MR procedures, but this tends be problematic primarily for objects made from conductive materials that have elongated shapes such as leads, guidewires, and certain types of catheters (e.g., catheters with thermistors or other conducting components).
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.
Simply insulating conductive material or separating it from the patient may not be sufficient to prevent excessive heating or burns from occurring. To prevent patients from experiencing excessive heating and possible burns in association with MR procedures, the following guidelines are recommended, in particular, prepare the patient for the MR procedure by ensuring that there are no unnecessary metallic objects contacting the patient’s skin.
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Defined by: Brian Titus, MD