Chapter 15: MRI Safety Mark D. Herbst, MD, PhD

Two main sources of danger Magnetic field RF Energy Also –Gradients –Acoustic noise

5 Gauss Line Generally regarded as safe

Magnetic field exposure No demonstrated biological effects in normal patients Internal objects-ferromagnetic –Metal in eyes—blindness? –Old steel aneurysm clips---movement/occlusion? –Implants or prostheses—depends on metal used— usually safe –Pacemakers—some say okay, but better safe than sorry –Use Shellock’s book or website

Magnetic field External objects—ferromagnetic only –Small projectiles –Large objects can pin a patient or cause harm

Gradients More heating with higher slew rates 6T/sec = safe Acoustic noise—use earplugs or headphones

RF energy Depositing energy like in a microwave oven! SAR = specific absorption rate (watts/kilo) –Depends on patient weight—do not lie! –Depends on imaging technique Surface burns –EKG leads

Responsibility of the TECH Make sure the pt has completed a screening form Keep unscreened people out of danger Listen to the patient when they are in the machine Refuse to scan patient if it may cause harm or if you are unsure.