Download Chapter 15: MRI Safety

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 www.mrisafety.com
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.