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.
Updated definition 2020:
More than 70% of MRI complications are caused by burns.1 MRI burns are typically prevented by screening patients for presence of ferrous material; this is done by “wanding” before entering the MRI suite.2 The most common causes of burns are from looped cables lying directly on the skin that transmit electromagnetic energy. Heating of implants may also cause burns if made from conductive materials.
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
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Other References
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