MRI Flashcards
….. act as a good MR nucleus
Hydrogen (1H,H+)
What does MRI utelize?
Hydrogen[protons] magnetic spin parallel to each other and present on radio-frequency pulses to produce image
Why are hydrogen atoms used in MRI?
Bcz they have a magnetic spin
When are atoms able to spin around themselves[unstable] ?
An atom that has an odd number of proton or neutron
When do you get signals from the protons to form an image?
The time it takes from excitation to relaxation time
which is called RELAXATION TIME
*How can you differentiate different tissues from each other?
Based on their different relaxation times they generate different image contrasts
When are protons spin vectors align perpendicular?
When an RF pulse is activated
when do protons go back to parallel alignment[aka in magnetic field]?
When RF [RADIOFREQUENCY] is disabled
Why do adipose[fat] tissue appear to have a brighter image than CSF?
Bcz fat tissue require less time to reach relaxation time due to the low density of fat and thus low signals received.
UNLIKE, in CSF[water] or bone are dense enough to appear dark due to the high signals received & the longer it takes for the protons to reach relaxation time
What is the magnet system formed from?
Superconductive coils
What is the most imp job of the coils?
Coils transmit several types of waves , the most imp is :Radio-frequency RF pulse to excite the protons
&
Then get the signals to the relaxed state
***what is the job of the radio-frequency coils(Transceiver)?
They transmit RF pulses to excite the protons and receive signals when the atoms relax
Which type of magnet is kept in a cold helium and nitrogen casing ?
Superconductive magnet
**which part of the MRI acts as both a transmitter and receiver?
The 2. Part of the MRI which is RF coils (Transceiver) ; THEY SEND RF PULSES TO EXCITE THE PROTONS
AND
RECEIVE THE SIGNALS WHEN THE PROTONS ARE RELAXING
**What are the 2 most imp electrical components of the MRI?
superconductive magnet & RF coils
What happens when the temperature in the superconductive magnet increases?
It causes temperature to increase and the magnet will overheat —> superconductivity is LOST —> RESISTANCE forms—> the cryogens [nitrogen and helium] will start boiling—>QUENCH [loss of magnetic feild]
How do you prevent contamination by external RF from affecting the image?
By having the MRI in a room with copper insulation=FARADAY CAGE
How do you prevent QUENCH?
By adding Cryogens [1lt/day] to keep the cold temperature
WHAT ARE THE INDICATIONS OF MRI?
1-having had a cheaper,easier test before
2-the pt doesn’t respond to initial medical tx and recommendations
3-when the pt has symptoms that cannot be explained
4-inc in pt symptoms
5-in support of other imaging methods
6-pts who will use direct MRI
Benefits of MRI?
- High soft tissue contrast
- Multiplanar imaging can be done
- No use of ionizing radiation
- Does not require iodinated contrast material
- Visualization of vascular structures
- Evaluation of cartilage tissue
- Visualization of the bony medulla
- Evaluation of many anatomical and functional structures in the same examination using a single modality
