Intensifying Screens Flashcards
What is the purpose of intensifying screens?
X-rays convert to what?
99% of the image comes from what?
1% of the image comes from direct interaction between what 2 things?
Who developed intensifying screens?
Purpose = amplify light beam to reduce patient dose
X-rays covert to light
99% of image comes from light conversion
1% of image comes from direct interaction between x-rays and film
Edison developed intensifying screens in 1896
What are the 4 layers of the intensifying screens and what are they composed of?
- Base = polyester
- Reflective Layer = titanium dioxide or magnesium oxide
- Phosphor = rare earth or calcium tungstate
- Protective Coat = plastic
What is the purpose of the base?
What is it made out of?
Specifications:
- uniformly ___
- not suffer ___ damage
- chemically ___ or ___
- ___ but sturdy
Purpose = serves as a support for other layers
Made out of = polyester (older materials: glass, cardboard)
Specifications:
- uniformly radiolucent
- not suffer radiation damage
- chemically inert or stable
- flexible but sturdy
What is the purpose of the reflective layer?
What is it composed of?
The reflective layer reduces what?
What does the reflective layer increase?
Reflective layer may cause loss of what?
Purpose = reflects light given off by phosphors back towards film
Composed of: thin layer of magnesium oxide or titanium dioxide
Reflective layer reduces = patient dose
Reflective layer increase = efficiency of screen
Reflective layer may cause loss of image sharpness (detail screens may not have this layer)
The phosphor layer is what layer of the intensifying screen?
The phosphor layer contains crystals that do what into what?
The phosphor layer is the “active” layer of the intensifying screen
The phosphor layer contains crystals that absorb x-ray photon energy into visible light
What layer lies closest to the film and is a plastic covering applied over the phospor layer?
The protective coat layer
What is the purpose of the protective layer?
Screens with sratches or chips will show what?
The protective layer helps eliminate what?
The protective layer is a durable surface for what?
The purpose of the protective layer is to limit abrasions and staining from use
Screens with sratches or chips will show white lines or chips artifact on image
The protective layer helps eliminate static electricity
The protective layer is a durable surface for cleaning the screens
Phosphors
What does the high atomic number of phosphor do?
What is conversion efficiency?
As conversion efficiency goes up, what goes down?
Phosphors
High atomic number of phosphor = increases probability of x-ray photon interaction
Conversion efficiency = ability to emit as much light per x-ray photon interaction as possible
As conversion efficiency goes up, patient radiation dose goes down
Spectral Emission
What is spectral emission?
What is luminescence?
What must spectral emission match?
Spectral Emission
Spectral emission = precise wavelength of light emitted by the phosphor
Luminescence = ability to emit light
Spectral emission must match film’s spectral sensitivity
Luminescence - 2 Types of Glow
- Fluorescence is ___ emission of ___ and stop glowing as soon as radiation ___ stops.
- Phosphorescence is screen ___ or after ___. Continues to glow for ___ time after exposure is ___.
Luminescence - 2 Types of Glow
- Fluorescence is instantaneous emission of light and stop glowing as soon as radiation exposure stops.
- Phosphorescence is screen lag or after glow. Continues to glow for short time after exposure is terminated.
Name the phosphor crystals used in the past and what color they emit
- Barium platinocyde (Roentgen used) = ultraviolet
- Zinc Sulfide = blue-purple
- Zinc Cadmium Sulfide = yellow-green
Calcium Tungstate (CAWO4)
- very ___ until the 1970s
- glows ___ (color)
- conversion efficiency is about ___%
- can be purchased in different ___ and ___
Calcium Tungstate (CAWO4)
- very popular until the 1970s
- glows ultraviolet blue (color)
- conversion efficiency is about 5%
- can be purchased in different speeds and resolution
Rare Earth Phosphor Crystals
- ___-___% conversion efficiency
- 4x faster than ___
What are the types of rare earth phosphor crystals and what colors do they emit?
Rare Earth Phosphor Crystals
- 15-20% conversion efficiency
- 4x faster than calcium tungstate (5%)
What are the types of rare earth phosphor crystals and what colors do they emit?
- yttrium = blue
- gadolinium = green
- lanthanum = oxybromide = blue & oxysulfide = green
Screens can be checked with what for problems?
UV light
What are 4 characteristics of the screen?
- Resolution - detail
- Speed - how slow or fast
- Contrast - gray scale
- Latitude
What is resolution?
Smaller crystals =
Larger crystals =
What are the 2 tests to measure resolution?
Resolution is the ability of an imaging system to ___ an object
Resolution is inversely related to what 2 things?
Resolution = ability of screen to accurately image an object (detail)
Smaller crystals = better detail (sharper)
Larger crystals = less detail (blur)
What are the 2 tests to measure resolution?
line pair test and wire mesh test (film-screen contact)
Resolution is the ability of an imaging system to accurately image an object
Resolution is inversely related to what 2 things?
- phosphor crystal size
- thickness of phosphor layer
Quantum Mottle (when you underexpose)
Each ___ crystal emits light that exposes a corresponding ___ crystal in the film
Why could an image appear grainy?
Quantum mottle can happen during ___ when using ___.
Digital: If you ___ the IR, you will get quantum mottle
Quantum Mottle (when you underexpose)
Each phosphor crystal emits light that exposes a corresponding silver crystal in the film
Why could an image appear grainy? If insufficient light is given off by phosphor crystal
Quantum mottle can happen during fluoroscopy when using low mA stations.
Digital: If you underexpose the IR, you will get quantum mottle
What is screen speed?
Smaller phosphor =
Larger phosphor =
Thin layer =
Thick layer =
Which 2 cause better and worse detail?
Screen speed = how fast the phosphor crystals respond to the x-rays
Smaller phosphor = slower the speed
Larger phosphor = faster the speed
Thin layer = slower the speed
Thick layer = faster the speed
Better detail = smaller phosphor and thin layer
Worse detail = larger phosphor and thick layer
Classification of Screen Speeds
Which rating uses words to describe speed?
Which rating uses numbers to describe speed?
Detail or slow = ___ (#)
Average (par) = ___(#)
Fast = ___ (#)
Classification of Screen Speeds
Which rating uses words to describe speed? Descriptive rating
Which rating uses numbers to describe speed? Relative speed rating
Detail or slow = less than 100
Average (par) = 100
Fast = greater than 100
Factors that Affect Relative Speed
Relative speed can be increased by increasing the factor(s) below
- ____ efficiency
- ___ efficiency
- ___ thickness
- ___ density
- ___ size
- Adding a ___
When does relative speed decrease?
Factors that Affect Relative Speed
Relative speed can be increased by increasing the factor(s) below
- Absorption efficiency
- Conversion efficiency
- Phosphor layer thickness
- Phosphor packing density
- Phosphor crystal size
- Adding a reflective layer
When does relative speed decrease? Phosphor dye is added
Contrast
Compared to a film taken with screens, screens will produce what type of image?
A higher contrast image
Advantages of using Intensifying Screens
- Reduces ___
- ___ exposure times
- ___ on images
- ___ improvement
- X-ray tube life is ___
- ___ can be used
Advantages of using Intensifying Screens
- Reduces patient’s radiation dose
- Shorter exposure times
- Less motion on images
- Contrast improvement
- X-ray tube life is longer
- Smaller FSS can be used
Radiographic Cassettes
- ___ case to house the film
- ___ exposure (nonscreen)
- ___ cassette
- ___ cassette
Radiographic Cassettes
- Light proof case to house the film
- Direct exposure (nonscreen)
- Screen cassette
- Grid cassette
Layers of the Cassette
- Front of the cassette =
- Compressions Device =
- Screen = ___ layers
- Film = ___ layers
- Thin foil layer =
- Back of cassette
Layers of the Cassette
- Front of the cassette = low atomic number
- Compressions Device = rubber or felt
- Screen = 4 layers
- Film = 4 layers
- Thin foil layer = stops backscatter radiation
- Back of cassette
