MRI MRI Safety 1 — Questions and Answers
Question 1: Which MRI zone is defined as the area containing the MRI scanner itself where the static magnetic field is always present?
- Zone I
- Zone II
- Zone III
- Zone IV (Correct answer)
Correct answer: Zone IV
Zone IV is the MRI scanner room where the magnet is always on and unrestricted ferromagnetic items pose immediate danger.
Question 2: A patient reports having a cardiac pacemaker. What is the standard MRI safety classification for most older pacemakers?
- MR Safe
- MR Conditional
- MR Unsafe (Correct answer)
- MR Compatible
Correct answer: MR Unsafe
Most older pacemakers are classified MR Unsafe because the magnetic field can interfere with device function or cause heating.
Question 3: What is the main biological risk associated with rapidly switching gradient magnetic fields during an MRI scan?
- Radiofrequency burns
- Peripheral nerve stimulation (Correct answer)
- Acoustic damage
- Hypothermia
Correct answer: Peripheral nerve stimulation
Rapidly switching gradients can induce electrical currents in body tissue, causing peripheral nerve stimulation (PNS).
Question 4: Which SAR limit (Specific Absorption Rate) is the FDA guideline for whole-body RF energy deposition in a 15-minute period for non-controlled conditions?
- 1.5 W/kg
- 2 W/kg
- 3 W/kg
- 4 W/kg (Correct answer)
Correct answer: 4 W/kg
The FDA guideline for whole-body average SAR under normal operating mode is 4 W/kg over any 15-minute period.
Question 5: A patient with a metallic foreign body in the eye should be evaluated with which imaging modality BEFORE entering the MRI suite?
- Ultrasound
- CT scan (Correct answer)
- Bone scan
- PET scan
Correct answer: CT scan
A CT scan of the orbits is used to detect metallic ocular foreign bodies before MRI because ferromagnetic metal near the eye is a contraindication.
Question 6: What term describes an object becoming a high-speed projectile when brought near a strong MRI magnetic field?
- Quenching effect
- Missile effect (Correct answer)
- Gradient artifact
- Susceptibility effect
Correct answer: Missile effect
The missile effect (or projectile effect) occurs when ferromagnetic objects are rapidly accelerated toward the bore by the strong static magnetic field.
MRI MRI Safety 1
Which MRI zone is defined as the area containing the MRI scanner itself where the static magnetic field is always present?