Free MRSO Static Magnetic Field Safety Questions and Answers

Question 1

An MR technologist is moving a patient into the bore of a 7T MRI scanner. The patient suddenly reports a strong sensation of vertigo and dizziness. What is the most likely physiological mechanism responsible for this effect?

Accepted Answer

Lorentz forces acting on ionic currents within the endolymph of the vestibular system.

Answer

The sensation of vertigo when moving into a strong static magnetic field is primarily caused by the magnetohydrodynamic effect. This involves the interaction between the static magnetic field (B0) and the naturally occurring ionic currents in the endolymph fluid of the inner ear's vestibular system. This interaction creates a Lorentz force that stimulates the semicircular canals, inducing a sense of motion or vertigo.

Question 2

Which of the following forces, exerted by the static magnetic field (B0), poses the most significant risk for projectile accidents in the MR environment?

Accepted Answer

Translational force

Answer

The translational force is the primary cause of the projectile effect. This force attracts ferromagnetic objects towards the magnet, accelerating them to dangerous speeds. The force is greatest where the spatial gradient of the magnetic field is highest, which is typically near the opening of the magnet bore.

Question 3

According to the American College of Radiology (ACR) Manual on MR Safety, what is the recommended controlled access area demarcation for the general public concerning the static magnetic field's fringe field?

Accepted Answer

The 5 Gauss (0.5 mT) line

Answer

The ACR recommends that access by the general public be restricted outside of the 5 Gauss (0.5 mT) line to prevent adverse effects on medical implants like pacemakers and to minimize projectile risks. The most recent IEC standard update suggests a 9-G line, but facilities following the more conservative 5-G line are still in compliance.

Question 4

A patient with an MR Conditional implant is scheduled for an MRI. The implant's labeling specifies it is safe for use in 1.5T scanners only. The MRSO is asked if the scan can be performed on the facility's 3T scanner, with the reasoning that a higher field strength is not necessarily more dangerous. What is the most appropriate response?

Accepted Answer

No, the conditions for safe use are specific to the static magnetic field strength tested, and safety cannot be assumed at different field strengths.

Answer

The safety of an MR Conditional device is only guaranteed under the specific conditions outlined in its labeling, which includes the static magnetic field strength (e.g., 1.5T). Safety at one field strength does not extrapolate to another, higher or lower. Factors like translational force, torque, and RF-induced heating can change unpredictably with the static field strength.

Question 5

Which of the following describes the translational force exerted by the static magnetic field on a ferromagnetic object?

Accepted Answer

The force is proportional to the product of the magnetic field strength and the spatial gradient of the field.

Answer

The translational force, which causes the projectile effect, is not uniform. It is dependent on both the strength of the static magnetic field (B0) and how rapidly that field strength changes over a distance (the spatial gradient). The force is maximized where the product of B0 and the spatial gradient is greatest, typically at the entrance to the magnet bore, and is actually near zero at the isocenter where the field is most homogeneous.

MRSO - Magnetic Resonance Safety Officer Practice Test

MRSO - Magnetic Resonance Safety Officer Practice Test

Free MRSO Static Magnetic Field Safety Questions and Answers