Safety

Question 1

What are magnetophosphene effects caused by?

Answer 1

A primary biological effect of time-varying magnetic fields on the eyes. Visual light flashes.

Question 2

Who may enter Zone 1?

Answer 2

general public

Question 3

Who may enter Zone 2?

Answer 3

unscreened MRI patients

Question 4

Who may enter Zone 3?

Answer 4

screened

MRI patients/personnel

Question 5

Who may enter Zone 4?

Answer 5

screened

patients under constant direct supervision of trained MR personnel

Question 6

What should be done if a patient cannot answer the screening questions convincingly?

Answer 6

a person who is qualified to answer questions about the patient’s
medical history, such as a physician, family member or a legal guardian, should complete the safety
interview

If a patient is unconscious and no family member or representative is available who knows the patient’s
medical history, physicians must determine if the MR examination is absolutely indicated. The patient
must be examined carefully for scars or any signs of previous surgeries or metal on or in the body, and
radiography or CT imaging should be performed and approved before continuing with the MR
examination. Physicians requesting the examination must sign special informed consent, and all
personnel involved should follow the facility’s policies and procedures.

Question 7

What are the categories used to describe device safety in MRI?

Answer 7

MR safe, MR conditional, MR unsafe

Question 8

What are the four main safety concerns relating to the static field?

Answer 8

Missile effect, Translational and rotational forces,
Safety for implanted hardware
RF or battery operated device malfunction
magnetohydrodynamic effect

Question 9

What are the three main safety concerns relating to the use of radiofrequencies (RF)?

Answer 9

RF can cause patient heating, heating in implanted wires and devices (antenna effect), and induced currents in the circuitry of implanted devices (such as pacemakers) causing malfunction.

Question 10

How can we reduce patient heating during an MRI scan?

Answer 10

Remove saturation pulses, increase the TR, decrease slice number, use an appropriate receive coil, avoid trains of 180° RF pulses, use parallel imaging techniques to reduce workload of phase encoding gradient, and reduce the flip angle of rephasing pulses.

Question 11

Why are cryogens dangerous?

Answer 11

frostbite, asphyxiation and rupture of the tympanic membranes

Question 12

What are the primary safety concerns relating to time-varying gradients?

Answer 12

peripheral nerve stimulation, 
visual light flash(magnetophosphenes)
muscle contractions,  
cardiac arrhythmias, 
noise

Question 13

The general public is limited to a magnetic field strength of _____

Answer 13

5 gauss

Question 14

Heart valves are acceptable for an mri scan of what field strength?

Answer 14

1.5 T

Question 15

The most important aspect of a safe MRI environment

Answer 15

Education

Question 16

Paitients in need of IV gadolinium contrast should have their GFR checked if they:

Answer 16

Are over 60
Have a history of hypertension
History of diabetes
History of renal disease

Question 17

Whole body FDA SAR limit

Answer 17

4 W / KG over 15 minutes

Question 18

FDA SAR limit for head

Answer 18

3 W / kg over 10 minutes

Question 19

FDA limit on time varying magnetic fields

Answer 19

Once patient experiences peripheral nerve stimulation

Question 20

What pulse sequence should be utilized the least in patient with implanted metallic hardware and why?

Answer 20

Gradient echo sequence. It lacks the 180 degree RF pulse that aids in correcting local magnetic field inhomogeneities found in metallic implants

Question 21

Difference between level 2 and level 1 personnel?

Answer 21

Level 1 personnel have limited training in MRI safety (knowledge of magnetic field)

Level 2 have extensive training in MRI safety, including vast knowledge of the main magnitude field and RF and gradient fields. Risks and biological effects

Question 22

FDA limits on magnetic field strength

Answer 22

4Tesla for the entire population, 8 Tesla for those over 1 month of age.