Flashcards in MRI Safety Deck (14)
What velocity has a paperclip have at 1.5T?
What is SAR?
Specific Absorption Rate.
The FDA limit for RF exposure is either an increase in body temperature or RF absorption and can be expressed in watts per kilogram (W/kg).
Name the most up-to-date MRI safety web site.
What does this sign mean?
(Yellow triangle - MR)
“MR Conditional—An item that has been demonstrated to pose no known hazards in a specified MRI environment with specified conditions of use.
Field conditions should be enumerated on the product, its packaging or in the enclosed literature.
Additional conditions, including specific configurations of the item (e.g., the routing of leads used for a neurostimulation system) may be required.”
Give three safety tips for a claustrophobic patient.
*Explain the procedure.
*Explain that the bore is open on both ends and give them a mirror so that they can see out.
*Patient position prone can be better than supine.
*Ask the patient to close their eyes and imagine they are somewhere nice! Place a cloth or mask over their eyes.
*Give the patient control and tell them that they do not have to have this examination, but explain why it is necessary.
*Give them a break and bring them out of the bore between sequences.
*Allow a relative or friend with then during the procedure.
*There is a bore light and fan that will help, but additional oxygen could help.
*Communicate with the patient!
*Offer them sedation.
What happens when a magnet quenches?
Helium escapes from the cryostat very fast.
This is a process of sudden loss of the absolute zero of temperature in the magnet coils so that the magnet cease to be superconductive and become resistive.
Can a pregnant patient undergo an MRI?
As yet there are also no known biological effects on fetuses in the MRI environment. There is however a number of mechanisms that could potentially cause adverse effects as a result of interactions of the electromagnetic fields with developing fetuses.
The FDA recommendation states: “If the information to be gained by MR would have required more invasive testing, MRI is acceptable”.
Most MRI units prefer to delay the examination till the second trimester and then have a signed consent form for pregnant patients. The American College of Obstetricians and Gynecologists recommends that pregnant patients should be reviewed on a case by case basis.
What is the predominant biological effect of the RF irradiation in MRI?
Heating of the patient’s tissue.
What is essential to give the patient before the MRI examination to help with the acoustic noise in the MRI environment?
Earplugs, earmuffs or headphones.
What is NSF?
Nephrogenic systemic fibrosis is a serious adverse reaction that may occur in patients that has received MRI contrast (gadolinium).
What objects can become projectiles in the MRI environment?
What is a fringe field?
The stray magnetic field outside the bore.
Which devices would be contra-indicated in an MRI examination?
Pacemakers, cochlear implants, some penile implants, certain bullets and shrapnel, carotid clips, aneurysm clips.