Intensifying Screens Flashcards
What is the function of the Intensifying screen?
to convert x-ray energy into visible light
What is the advantage of the intensifying screen?
To reduce patient exposure
What are the four layers of an intensifying screen?
- Base
- Reflective layer
- Phosphor layer
- Protective coating
What does the base do?
- Mechanically supports the phosphor
- Composed of high-grade cardboard or polyester
Base must have 5 characteristics. What are they?
- Rugged
- Moisture Resistance
- Chemically inert (doesn’t interfere with phosphor)
- Flexible
- No impurities
What does the reflective layer do?
Intercepts the wayward light photons and redirects them toward the film
- # of light photons directed to film is nearly doubled
What does the phosphor layer do?
The phosphor emits light when struck by x-rays
The phosphor layer is also known as the ________?
Active layer
What are the four different characteristics of the phosphor layer?
- High Atomic #
- High Conversion efficiency
- Spectral Matching
- Minimal afterglow or screen lag
Why is high atomic number important in the phosphor layer?
makes for high absorption rate
Why is high conversion efficiency important in phosphor layer?
a good phosphor is one that uses minimal x-rays to produce maximum light
Why is spectral matching important in the phosphor layer?
If there is a mismatch, speed is lost and will result in increase of exposure to obtain the same efficiency characteristics
- Film must be sensitive to the color being emitted from the screen– has NOTHING to do with film color.
Why is minimal afterglow or screen lag important in the phosphor layer?
If the screen continues to glow even after interaction with x-rays have ceased, this will result in increased density on the film
What is Luminescence?
any material that emits light in response to some outside stimulation
What is phosphorescence?
continues to emit light after stimulation ceases. Screen lag or Afterglow
- BAD
What is Fluorescence?
visible light emitted only during stimulation. No lag
- GOOD (what we want)
What are the two types of phosphors?
- Calcium Tungstate
- Rare earth phosphors
- Based on manufacturer. Constructed singly or in combination
What are rare earth phosphors?
- higher conversion efficiency
- almost twice as fast than calcium tungstate–> means mA can be cut in half reducing patient exposure
What are some elements of rare earth phosphors?
- Gadolinium
- Lanthanum
- Yttrium
