Safety Flashcards
What are magnetophosphene effects caused by?
A primary biological effect of time-varying magnetic fields on the eyes. Visual light flashes.
Who may enter Zone 1?
general public
Who may enter Zone 2?
unscreened MRI patients
Who may enter Zone 3?
screened
MRI patients/personnel
Who may enter Zone 4?
screened
patients under constant direct supervision of trained MR personnel
What should be done if a patient cannot answer the screening questions convincingly?
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.
What are the categories used to describe device safety in MRI?
MR safe, MR conditional, MR unsafe
What are the four main safety concerns relating to the static field?
Missile effect, Translational and rotational forces,
Safety for implanted hardware
RF or battery operated device malfunction
magnetohydrodynamic effect
What are the three main safety concerns relating to the use of radiofrequencies (RF)?
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.
How can we reduce patient heating during an MRI scan?
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.
Why are cryogens dangerous?
frostbite, asphyxiation and rupture of the tympanic membranes
What are the primary safety concerns relating to time-varying gradients?
peripheral nerve stimulation, visual light flash(magnetophosphenes) muscle contractions, cardiac arrhythmias, noise
The general public is limited to a magnetic field strength of _____
5 gauss
Heart valves are acceptable for an mri scan of what field strength?
1.5 T
The most important aspect of a safe MRI environment
Education
Paitients in need of IV gadolinium contrast should have their GFR checked if they:
Are over 60
Have a history of hypertension
History of diabetes
History of renal disease
Whole body FDA SAR limit
4 W / KG over 15 minutes
FDA SAR limit for head
3 W / kg over 10 minutes
FDA limit on time varying magnetic fields
Once patient experiences peripheral nerve stimulation
What pulse sequence should be utilized the least in patient with implanted metallic hardware and why?
Gradient echo sequence. It lacks the 180 degree RF pulse that aids in correcting local magnetic field inhomogeneities found in metallic implants
Difference between level 2 and level 1 personnel?
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
FDA limits on magnetic field strength
4Tesla for the entire population, 8 Tesla for those over 1 month of age.
