Notes Flashcards
Four Components of MRI?
- Magnetic Field
- Radio Frequency
- Gradient Coils
- Cryogens
Problem with magnetic field?
- Invisible
- Pulls in Translational Force (missle effect)
- Pulls in Torque force (twist effect)
Two types of pull?
Translational and Torque
What is the point of no return?
The point where the magnetic force pulls in a ferromagnetic object and would be unable to be stopped.
Fringe Field
The stray magnetic field outside the bore of the magnet is known as the fringe field and this is a 3 dimensional field measured in Gauss. MRI systems are shielded to confine the fringe field within the scan room.
How is the edge of the fringe field restricted so it doesn’t spill into adjacent rooms?
Active Shielding
Active Shielding
Brings in the fringe field through increasing tesla by coil use.
-the magnetic field can be neutralized by another instrument which emits an opposite magnetic field of equivalent value, thus eliminating the residual field in a limited space.
-5 gauss line is where it is safe for someone not screened for MRI (LCNI)
Issue: acceleration of metal objects is further multiplied
Benefits of shielding
- MRI can be in smaller space/room
- Edge of fringe field brought closer to the MRI magnet
End of the fringe field?
Called the 5 gauss line
Radio Frequency Issues
heating (SAR), conductance, materials (loop in cord, skin on skin)
MRI radiofrequencies are just as dangerous as xrays or ct scans
False
SAR
Specific Absorption
weight
RF energy
-Absorbed by tissue –> heat accumulated within subject
Gradient Coils
-Deliberate variation to magnetic field
-Extreme noise (EPI)
-Peripheral Nerve Stimulation (tingly/painful)
To prevent peripheral nerve stimulation
Make sure arms & legs aren’t crossed. Make sure to bring participant out of machine if stimulation continues.
Cryogens
Quench
-releases the helium immediately, heating up the superconductive coil and dropping the magnetic field in a matter of minutes
Could cause frost bite
-Quench leak could lead to asphyxiation hazard
-Ear drum rupture
-Fire hazard
When to Quench
Only Quench if life or limb are in danger
–Take participant out of room
–Contact MRI manufacturer to refill helium
Liquid helium runs through power, keep liquid helium cold
True
Has anyone ever been killed from MRI
yes
Biggest danger for anyone in MRI enviornment?
Metal being pulled in?
Paperclip/bobby pin can reach
40 mph before reaching center of magnet
Would power outage make MRI lose magnetic field?
No
Before going to magnet bay what should safety trained staff do
pat themselves down, do checks to ensure they didn’t forget anything (like bobby pins)
Your subject arrived early, what to do?
- Have subject spin on the ferromagnetic detector and troubleshoot any red lights
- Remind the participant of the length of the scan and encourage them to use the restroom
- Remove all piercings, jewelry, or items in pocket. Place in locker.
- Give the scan operator the screening form so they can type the participant information
- Remove any antimicrobial materials
Manufactures claim to produce anti-bacterial clothing. What is in this clothing? Is it safe to scan someone who is wearing this material?
-Lulu lemon/under armor
-copper/silver
-no, it could heat up and burn participant
Ferromagentic detector
Only detects ferromagnetic items (won’t detect clothing with copper/silver so make sure to check).
Gradient Coils
Creates magnetic field that turns on/off quickly and fights with magnetic field, very loud
What secondary effect can these magnetic fields turning on and off cause in human bodies?
Hearing loss
Why is it important we collect correct height and weight accurately on screening form? What could happen if height and weight aren’t accurate?
SAR (Specific Absorption Rate) based on H/W that allows us to know how much RF they can be exposed to. If H/W not accurate, they could be over exposed to RF their body can’t handle.
If you have to scan a larger participant and their elbows bump agains the inside of the scanner bore, what steps should be taken to protect subject? what are you trying to protect?
Use 1cm pad to separate and insulate from direct contact. Otherwise, they could get burned.
What is the #1 concern of liquid helium with regard to anyone in the room?
Asphyxiation from helium displacing all the oxygen from the room.
How will participant get your attention during scan?
Participant can use the squeeze ball.
If your participants scan looks abnormal to you, what should you do?
Let scan operators know so they can send it to the appropriate individuals to get it checked out.
If participant has medical implant what needs done before MRI is scheduled?
1.Email LCNI staff to ensure if surgery/implant is safe.
2. Have the subject contact the medical facility to acquire implant records
3. Have participant acquire make and model of the implanted device to verify implant safety.
4.Make note of the implant and communicate with LCNI before the participant is scheduled.
Some people don’t know or forgot if they were claustrophobic
True
How many safety trained individuals are needed for a scan session in research? Is it better to have more?
2 are required, 3 is acceptable, more than that is discouraged/ (not allowed)? due to potential distractions.
