MRI Safety Flashcards

Under IEC normal operating mode, what is the whole-body averaged SAR limit?

Answer: 2 W/kg

Normal operating mode limits whole-body SAR to 2 W/kg, while first level controlled mode allows up to 4 W/kg.

If all other parameters stay the same, how does SAR change when a patient moves from a 1.5T to a 3T scanner?

Answer: It roughly quadruples

SAR is proportional to the square of the static field strength, so doubling B0 roughly quadruples SAR.

Which ACR safety zone is the MR scanner room itself?

Answer: Zone IV

Zone IV is the magnet room and must be clearly marked and accessible only under direct MR personnel supervision.

Which MR labeling symbol is a red circle with a diagonal line through it?

Answer: MR Unsafe

Under ASTM F2503, MR Unsafe items are labeled with a red circle and a diagonal slash.

Which force on a ferromagnetic object depends most directly on the spatial field gradient, not just field strength?

Answer: Translational (projectile) force

Translational attraction depends on the spatial gradient of the static field, which is often greatest near the bore entrance.

What is the main purpose of having a patient avoid crossed legs or hands clasped during scanning?

Answer: To prevent conductive loops that can cause RF burns

Skin-to-skin contact can form a closed conductive loop in which RF energy induces current, causing burns.

A metalworker reports possibly getting metal in his eye years ago but has no documentation. What is the most appropriate step before MRI?

Answer: Get orbital radiographs to screen for a foreign body

Orbit radiographs are the standard way to screen for intraocular metal, which could move and cause blindness.