Radiofrequency Safety for Interventional MRI Procedures 1

Abstract

During an interventional magnetic resonance imaging (MRI) procedure, various kinds of surgical and interventional devices, such as needles, catheters, and guidewires, that contain metallic components are used inside the MRI scanner. Interference of these devices with radiofrequency pulses is known to be a possible health risk. The radiofrequency (RF) power delivered by an RF body coil may become concentrated on these metallic devices and may cause a significant increase in the specific absorption rate (SAR), potentially resulting in excessive local temperature rise and burns (1). This risk is very well known and has been extensively studied (2). The source of this problem is also well known (3). This temperature rise has been shown in a multitude of studies by many investigators (4‐8). Unfortunately, absolute values of the results are conflicting, primarily because the methods used in these measurements have not been uniform. In addition, guidelines that could be used to prevent this problem from occurring in humans have not been established. During an MRI procedure, RF pulses are applied to the subject in order to excite the spins and generate echo signals, which are used to generate images. As an undesired side effect, the temperature of the subject increases as a result of absorption of the RF energy (9). The amount of applied RF energy depends on the pulse sequence that is being used, the type of the coil that is used to transmit this energy to the body, and the size, shape, and electromagnetic and thermodynamic properties of the body. This effect is very well known and various guidelines that are in place are safely used (10). Reported RF safety problems are only related to the use of metallic devices that come into contact with the body (11). The existence of metallic devices inside or in contact with the body during an MRI examination is infrequent. As a safety precaution, during routine diagnostic examinations, patients are asked to remove all the metallic objects that may be in contact with their body. With few exceptions, the presence of metallic implants is a contraindication for MRI examinations. When the subject is free from metallic devices, an MRI examination can be conducted very safely with current guidelines, as used in approximately 2 million examinations per year.