Magnetic resonance imaging (MRI) is a method that has evolved continuously during the past 20 years, yielding MR systems with stronger static magnetic fields, faster and stronger gradient magnetic fields, and more powerful radiofrequency transmission coils. It is increasingly being used and requested as several new indications have been established during the last few years—for example, cardiovascular MRI.

To evaluate the contraindications to MRI is equivalent to understanding the safety issues surrounding the use MRI.

MRI is often described as a “safe” modality due to the fact that, unlike x ray based systems, ionising radiation is not involved. However, there are hazards intrinsic to the MR environment that must be acknowledged and excluded. Most reported cases of MR related injuries and the few fatalities that have occurred have apparently been the result of failure to follow safety guidelines or have resulted from the use of inappropriate or outdated information related to the safety aspects of biomedical implants and devices. Therefore, for information on specific guidelines and devices, detailed sources of safety information—for example, dedicated websites (box 1)—are recommended.1 2 ^{w1 w2}

Risks associated with MRI may be attributed to one or to a combination of the three main mechanisms of the system:

1. Strong static magnetic fields—As a result of ferromagnetic interactions, an object or device may be moved, rotated, dislodged, or accelerated toward the magnet. The “projectile effect” means that, depending on the type of magnet and the intensity of the generated field, to varying extent, objects are attracted to the centre of the magnet (for example, helium or oxygen cylinders, ventilators, wheelchair, etc), possibly causing severe injuries and damage. Furthermore, articles such as metallic splinters, vascular clips, and cochlear implants may be dislodged. The strong magnetic field may also affect device function, as most, but importantly not …