Guidelines to Prevent Excessive Heating and Burns Associated with Magnetic Resonance Procedures*
Magnetic resonance (MR) imaging is a relatively safe diagnostic modality. However, damaged radiofrequency coils, physiologic monitors, electronically-activated devices, and external accessories or objects made from conductive materials have caused excessive heating, resulting in burn injuries to patients undergoing MR procedures. Heating of implants and similar devices may also occur, but this tends to be problematic primarily for objects made from conductive materials that have elongated shapes or that form loops of a certain diameter. For example, excessive MRI-related heating has been reported for leads, guidewires, catheters (e.g., catheters with thermistors or other conducting components), and external fixation systems, and cervical fixation systems.
In the United States, many incidents of excessive heating have been reported in patients undergoing MR procedures that were unrelated to equipment problems or the presence of conductive external or internal implants or materials review of data files from U.S. Food and Drug Administration, Center for Devices and Radiological Health, Manufacturer and User Facility Device Experience Database, MAUDE. In a review of the MAUDE database over a 10 year period, Hardy and Weil (2010) indicated that 419 thermal injuries were associated with MRI.
These incidents included first, second, and third degree burns that were experienced by patients. In many of these cases, the reports indicated that the limbs or other body parts of the patients were in direct contact with transmit body radiofrequency (RF) coils or other transmit RF coils of the MR systems. In other cases, skin-to-skin contact points were suspected to be responsible for these injuries, however, the exact mechanism responsible for these incidents is unknown.
MR systems require the use of RF pulses to create the MR signal. This RF energy is transmitted through free space from the transmit RF coil to the patient. When conducting materials are placed within the RF field, a concentration of electrical currents sufficient to cause excessive heating and tissue damage may occur. Therefore, only devices with carefully designed current paths can be made safe for use during MR procedures. Simply insulating conductive material (e.g., wire or lead) or separating it from the patient may not be sufficient to prevent excessive heating or burns from occurring for some devices.
Furthermore, certain elongated shapes (i.e. depending on the length and the transmit RF frequency) exhibit the phenomenon of “resonance” that increases their propensity to concentrate RF currents. At the operating frequencies of present day MR systems, conducting loops of tens of centimeters in size can create problems and must be avoided, unless high impedance techniques are used to limit the RF current. Importantly, even loops that include small gaps separated by insulation may still conduct currents.
Pietryga et al. (2013) reported a case of a thermal burn that occurred during MRI that was likely caused by invisible silver embedded microfibers in the fabric of an undershirt. As the prevalence of fabrics containing nondetectable metallic microfibers increases for use in athletic clothing or other garments, the importance of having patients change into gowns or other appropriate attire that do not contain metallic materials is advised as another means of preventing MRI-related burns.
To prevent excessive heating and possible burns in association with MR procedures, the following guidelines are recommended:
- The patient should change into a gown or other appropriate attire that does not contain metallic material.
- Prepare the patient for the MR procedure by ensuring that there are no unnecessary metallic objects contacting the patient’s skin (e.g., drug delivery patches with metallic components, jewelry, necklaces, bracelets, key chains, etc.).
- Prepare the patient for the MR procedure by using insulation material (i.e. appropriate padding) to prevent skin-to-skin contact points and the formation of “closed-loops” from touching body parts.
- Insulating material (minimum recommended thickness, 1-cm) should be placed between the patient’s skin and transmit RF coil that is used for the MR procedure (alternatively, the transmit RF coil itself should be padded). There should be no direct contact between the patient’s skin and the transmit RF body coil of the MR system. This may be accomplished by having the patient place his/her arms over his/her head or by using elbow pads or foam padding between the patient’s tissue and the transmit RF body coil of the MR system. This is especially important for MR examinations that use the transmit RF body coil or other large RF coils for transmission of RF energy.
- Use only electrically conductive devices, equipment, accessories (e.g., ECG leads, electrodes, etc.), and materials that have been thoroughly tested and determined to be safe or otherwise acceptable for MR procedures.
- Carefully follow the MR Safe or MR Conditional criteria and recommendations for implants and devices made from electrically-conductive materials (e.g., bone fusion stimulators, neurostimulation systems, cardiac devices, cochlear implants, etc.).
- Before using electrical equipment, check the integrity of the insulation and/or housing of all components including surface RF coils, monitoring leads, cables, and wires. Preventive maintenance should be practiced routinely for such equipment.
- Remove all non-essential electrically conductive materials from the MR system prior to the MR procedure (i.e. unused surface RF coils, ECG leads, EEG leads, cables, wires, etc.).
- Keep electrically conductive materials that must remain in the MR system from directly contacting the patient by placing thermal and/or electrical insulation between the conductive material and the patient.
- Keep electrically conductive materials that must remain within the transmit body RF coil or other transmit RF coil from forming conductive loops. Note: The patient’s tissue is conductive and, therefore, may be involved in the formation of a conductive loop, which can be circular, U-shaped, or S-shaped.
- Position electrically conductive materials to prevent “cross points”. A cross point is the point where a cable crosses another cable, where a cable loops across itself, or where a cable touches either the patient or sides of the transmit RF coil more than once. Even the close proximity of conductive materials with each other should be avoided because cables and RF coils can capacitively-couple (without any contact or crossover) when placed close together.
- Position electrically conductive materials (e.g., cables, wires, etc.) to exit down the center of the MR system, not along the side of the MR system or close to the transmit RF body coil or other transmit RF coil.
- Do not position electrically conductive materials across an external metallic prosthesis (e.g., external fixation device, cervical fixation device, etc.) or similar device that is in direct contact with the patient.
- Allow only properly trained individuals to operate devices (e.g., monitoring equipment) in the MR environment.
- Follow all manufacturer instructions for the proper operation and maintenance of physiologic monitoring or other similar electronic equipment intended for use during MR procedures.
- Electrical devices that do not appear to be operating properly during the MR procedure should be removed from the patient immediately.
- RF surface coil decoupling failures can cause localized RF power deposition levels to reach excessive levels. The MR system operator will recognize such a failure as a set of concentric semicircles in the tissue on the associated MR image or as an unusual amount of image non-uniformity related to the position of the transmit RF coil.
- Do not permit patients to wear clothing items (e.g., sportswear, underwear, yoga pants, etc.) that have metal-based fibers.
- Closely monitor the patient during the MR procedure. If the patient reports sensations of heating or other unusual sensation, discontinue the MR procedure immediately and perform a thorough assessment of the situation.
The adoption and regular practice of these guidelines will ensure that patient safety is maintained, especially as more conductive materials and electronically-activated devices are used in association with MR procedures.
Abdel-Rehim S, et al. Burns from ECG leads in an MRI scanner: Case series and discussion of mechanisms. Ann Burns Fire Disasters 2014;27:215-8.
Bashein G, Syrory G. Burns associated with pulse oximetry during magnetic resonance imaging. Anesthesiology 1991;75:382-3.
Bennett MC, et al. Mechanisms and prevention of thermal injury from gamma radiosurgery headframes during 3T MR imaging. J Appl Clin Med Phys 2012;13:3613.
Brown TR, Goldstein B, Little J. Severe burns resulting from magnetic resonance imaging with cardiopulmonary monitoring. Risks and relevant safety precautions. Am J Phys Med Rehabil 1993;72:166-7.
Chou C-K, et al. Absence of radiofrequency heating from auditory implants during magnetic resonance imaging. Bioelectromagnetics 1997;44:367-372.
Dempsey MF, Condon B. Thermal injuries associated with MRI. Clin Radiol 2001;56:457-65.
Dempsey MF, Condon B, Hadley DM. Investigation of the factors responsible for burns during MRI. J Magn Reson Imag 2001;13:627-631.
Diaz F, Tweardy L, Shellock FG. Cervical fixation devices: MRI issues at 3-Tesla. Spine 2010;35:411-5.
ECRI Institute. Health Devices Alert. A new MRI complication? Health Devices Alert May 27, pp. 1, 1988.
ECRI Institute. Thermal injuries and patient monitoring during MRI studies. Health Devices Alert 1991;20:362-363.
ECRI Institute. Hazard Report. Patients can be burned by damaged MRI AV entertainment systems. Health Devices 2008;37:379-80
Friedstat JS, et al. An unusual burn during routine magnetic resonance imaging. J Burn Care Res 2013;34:e110-1.
Haik J, Daniel S, et al. MRI induced fourth-degree burn in an extremity, leading to amputation. Burns 2009;35:294-6.
Hall SC, Stevenson GW, Suresh S. Burn associated with temperature monitoring during magnetic resonance imaging. Anesthesiology 1992;76:152.
Hardy PT, Weil KM. A review of thermal MR injuries. Radiol Technol 2010;81:606-9.
Heinz W, Frohlich E, Stork T. Burns following magnetic resonance tomography study. Z Gastroenterol 1999;37:31-2.
International Commission on Non-Ionizing Radiation Protection (ICNIRP) statement, medical magnetic resonance procedures: Protection of patients. Health Physics 2004;87:197-216.
Jacob ZC, et al. MR imaging-related electrical thermal injury complicated by acute carpal tunnel and compartment syndrome: Case report. Radiology 2010;254:846-50.
Jones S, Jaffe W, Alvi R. Burns associated with electrocardiographic monitoring during magnetic resonance imaging. Burns 1996;22:420-421.
Kainz W. MR heating tests of MR critical implants. J Magn Reson Imag 2007;26:450-1.
Expert Panel on MR Safety, Kanal E, Barkovich AJ, et al. ACR guidance document on MR safe practices: 2013. J Magn Reson Imag 2013;37:501-30.
Kanal E, Shellock FG. Burns associated with clinical MR examinations. Radiology 1990;175:585.
Kanal E, Shellock FG. Policies, guidelines, and recommendations for MR imaging safety and patient management. J Magn Reson Imag 1992;2:247-248.
Karoo RO, et al. Full-thickness burns following magnetic resonance imaging: A discussion of the dangers and safety suggestions. Plast Reconstr Surg 2004;114:1344-1345.
Keens SJ, Laurence AS. Burns caused by ECG monitoring during MR imaging. Anaesthesia 1996;51:1188-9.
Kim LJ, et al. Scalp burns from halo pins following magnetic resonance imaging. Case Report. Journal of Neurosurgery 2003:99:186.
Knopp MV, et al. Unusual burns of the lower extremities caused by a closed conducting loop in a patient at MR imaging. Radiology 1996;200:572-5.
Kugel H, et al. Hazardous situation in the MR bore: Induction in ECG leads causes fire. Eur Radiol 2003;13:690-694.
Lange S, Nguyen QN. Cables and electrodes can burn patients during MRI. Nursing 2006;36:18.
Nakamura T, et al. Mechanism of burn injury during magnetic resonance imaging (MRI)-simple loops can induce heat injury. Front Med Biol Eng 2001;11:117-29.
Newcombe VF, et al. Potential heating caused by intraparenchymal intracranial pressure transducers in a 3-Tesla magnetic resonance imaging system using a body radiofrequency resonator: Assessment of the Codman MicroSensor Transducer. J Neurosurg 2008;109:159-64.
Nyenhuis JA, et al. Heating near implanted medical devices by the MRI RF-magnetic field. IEEE Trans Magn 1999;35:4133-4135.
Pietryga JA, et al. Invisible metallic microfiber in clothing presents unrecognized MRI risks for cutaneous burns. Am J Neuroradiol 2013;34:E47-50.
Ruschulte H, Piepenbrock S, Munte S, Lotz J. Severe burns during magnetic resonance examination. Eur J Anaesthesiol 2005;22:319-320.
Scheel M, et al. Evaluation of intracranial electrocorticography recording strips and tissue partial pressure of oxygen and temperature probes for radio-frequency-induced heating. Acta Neurochir Suppl. 2013;115:149-52.
Shellock FG. Radiofrequency-induced heating during MR procedures: A review. J Magn Reson Imag 2000;12: 30-36.
Shellock FG, Crues JV. MR procedures: Biologic effects, safety, and patient care. Radiology 2004;232:635-652.
Shellock FG, Slimp G. Severe burn of the finger caused by using a pulse oximeter during MRI. Am J Roentgenol 1989;153:1105.
Tanaka R, et al. Overheated and melted intracranial pressure transducer as cause of thermal brain injury during magnetic resonance imaging. J Neurosurg 2012;117:1100-9.
Takahashi T, et al. MRI-related thermal injury due to skin-to-skin contact. Eur J Dermatol 2016;26:296-8.
Tjalma WA. Burning of an ulcerated breast cancer during MRI: A lesson to be learned. JBR-BTR 2014;97:125.
Tsai LL, et al. A practical guide to MR imaging safety: What radiologists need to know. Radiographics 2015;35:1722-37.
Wright BB, et al. A neck burn of unexpected etiology during magnetic resonance imaging of a one year old boy. J Clin Anesth 2014;26:86-7.
Yamazaki M, et al. Investigation of local heating caused by closed conducting loop at clinical MR imaging: Phantom study. Nippon Hoshasen Gijutsu Gakkai Zasshi 2008;20;64:883-5.