The physics of MRI safety

Abstract

The main risks associated with magnetic resonance imaging (MRI) have been extensively reported and studied; for example, everyday objects may turn into projectiles, energy deposition can cause burns, varying fields can induce nerve stimulation, and loud noises can lead to auditory loss. The present review article is geared toward providing intuition about the physical mechanisms that give rise to these risks. On the one hand, excellent literature already exists on the practical aspect of risk management, with clinical workflow and recommendations. On the other hand, excellent technical articles also exist that explain these risks from basic principles of electromagnetism. We felt that an underserved niche might be found between the two, ie, somewhere between basic science and practical advice, to help develop intuition about electromagnetism that might prove of practical value when working around MR scanners. Following a wide‐ranging introduction, risks originating from the main magnetic field, the excitation RF electromagnetic field, and switching of the imaging gradients will be presented in turn. Level of Evidence: 5 Technical Efficacy: 1 J. Magn. Reson. Imaging 2018;47:28–43.

Magnetic Resonance Imaging System–Driven Medical Robotics

“…The main (static) magnetic field of current human MRI scanners is typically 1.5 or 3 T, which are the ones mostly available in clinics, and it is possible to see even 10.5 T (which is about 200 000 times stronger than the magnetic field of earth) in preclinical environments . Such strong magnetic fields can be highly dangerous as they can exert strong forces and torques on any magnetic material coming close to MRI.…”

“…However, cardiac stimulation can be of high risk. In the current clinical systems, cardiac stimulation does not seem to be a risk, but some research systems, in theory, have the potential to stimulate cardiac tissue . The effect on metallic devices in the human body or inside MRI is also a point to consider about safety.…”

Magnetic Resonance Imaging of Myocardial Deformation and Scarring in Coronary Artery Disease.

“…Because MRI does not employ ionizing radiation, referring physicians may consider MRI examinations to pose no risk to the patient [30]. There are, however, some important aspects to consider.…”

“…When the gradients change polarity, vibrations in the gradient coils produce noise, which becomes louder with increasing slew rate [30] and field strength [32]. Patients must therefore wear ear protectors [33].…”

“…The changing gradients can also cause nerve stimulation, which can have discomforting effects such as finger contractions [30]. At high magnetic field strengths, such as 7 Tesla, vestibular effects are common [34].…”