MRI Safety Flashcards

During a magnet quench, what is the main danger to people in the scan room if the quench pipe fails?

Answer: Asphyxiation and cryogenic burns from helium gas

Boiling helium can displace oxygen and cause frostbite, so the room should be evacuated at once.

Rapidly switching gradient fields (dB/dt) most directly cause which effect?

Answer: Peripheral nerve stimulation

Fast-changing gradient fields induce currents in tissue that can stimulate peripheral nerves and cause tingling or twitching.

Which patient has the highest risk of nephrogenic systemic fibrosis after receiving gadolinium?

Answer: eGFR below 30 mL/min/1.73 m² or on dialysis

NSF risk is mainly in severe chronic kidney disease or acute kidney injury, especially with higher-risk (group I) agents.

What is the FDA guideline limit for peak unweighted sound pressure level in MRI?

Answer: 140 dB

FDA guidance sets the peak unweighted sound pressure limit at 140 dB, and hearing protection is required for all patients.

A patient has a medication patch with a metallic foil backing. What is the main safety concern?

Answer: RF heating that can burn the skin

Metallic backing can heat during RF transmission, so these patches are usually removed before scanning with the prescriber's approval.

Why does an ECG tracing inside the magnet often show an elevated T wave?

Answer: The magnetohydrodynamic effect of blood flowing in the static field

Ionic blood moving through the static field creates a voltage that adds to the ECG, mostly during the T wave.

An MR Conditional implant's labeling specifies a B1+rms limit. What does this parameter describe?

Answer: The time-averaged RF transmit field magnitude

B1+rms is the root-mean-square RF transmit field, a more accurate measure of RF exposure for implants than SAR.