MRI Safety

Will Morton, a staff writer for AuntMinnie.com, published an article about safety issues during magnetic resonance imaging. It begins

As the push toward stronger and faster MRI scanners continues, so does concern over magnet safety, according to Filiz Yetisir, who discussed the potential effects MRI has on patients at the recent International Society for Magnetic Resonance in Medicine virtual meeting (ISMRM 2021).

Main Magnet

An MRI device creates a magnetic field having a strength of several tesla. Any magnetic objects near the device can be sucked into the main field, becoming dangerous projectiles. For instance, in 2001 a six-year-old was killed by an oxygen cylinder. Yetisir warns: “Remember, the magnet’s always on.”

Gradient Coils

The gradient coils used during imaging produce magnetic fields much weaker than the dc main field, but they are turned on and off throughout the imaging pulse sequence. This causes two safety concerns. 1) The changing magnetic field induces eddy currents in the patient, which can stimulate nerves—an effect similar to transcranial magnetic simulation. 2) The switching of current in the gradient coils creates mechanical vibrations, leading to noise so loud that ear plugs may be needed to prevent hearing loss.

Radiofrequency Fields

A radiofrequency magnetic field—which rotates the spins into the plane perpendicular to the main magnet—is an essential part of any MRI pulse sequence. This field can induce eddy currents that heat the tissue. Generally the field isn’t strong enough to cause significant heating, but if a person has metal implants or tattoos, the heating may be increased locally. Any implanted medical device, such as a pacemaker, can interact with all three types of magnetic fields.

Gadolinium

One issue Morton’s article doesn’t discuss is the toxicity of contrast agents such as gadolinium used in some MRI studies.

AuntMinnie.com is one of those websites that’s valuable for readers of Intermediate Physics for Medicine and Biology.

Screenshot of AuntMinnie.com

AuntMinnie.com provides the first comprehensive community internet site for radiologists and related professionals in the medical imaging industry.

We provide a forum for radiologists, business managers, technologists, members of organized medicine, and industry to meet, transact, research, and collaborate on topics within the field of radiology with the ease and speed that only the internet can provide.

AuntMinnie features the latest news and information about medical imaging. Staff members include executives, editors, and software engineers with years of experience in the radiology industry.

AuntMinnie.com reminds me of the Physicsworld medical physics website. Physicsworld is associated with the Institute of Physics, the main physics professional society in the United Kingdom. AuntMinnie is run by a consulting firm, the Science and Medicine Group of Arlington, Virginia. Both websites provide useful information about innovations and news in medical physics. 

For more information about MRI safety, see MRIsafety.com. For more information about the physics underlying these safety issues, see Chapter 18 of IPMB.